Computer World

Using the Blogger Template

2008-11-20T22:54:00.000-08:00

1. Click on the Get Template link to download the script and images.

2. If you do not already have a Photobucket account create a free one and upload the images there. Make sure to select the 17" screen size before uploading.

3. After uploading Copy the URL (without the file name.) which appears in the textbox below the uploaded image.

4. Open the template script file in Notepad.

5. Find and Replace http://replace.photobucket.com/albums/replace/ with the URL you copied from the textbox which should look something like this http://i20.photobucket.com/albums/j432/usename/

6. Now Copy the entire text in the script file and Paste into your blogger template.

7. Save and then Republish.

8. If you receive the following error message 'Your template could not be parsed as it is not well-formed. Please make sure all XML elements are closed properly.
XML error message: The markup in the document preceding the root element must be well-formed.' scroll down the page and click on Revert to Classic Template.

Get of Dollar of with Google Adsense

2008-10-22T03:10:00.000-07:00

One again article about Google Adsense

Google Adsense, program the affiliasi for the business of very internet of] popular in world online in this time. Everybody can participate to become the advertiser for google on condition that easy to and quickly, enough by placing advertisement google in their situs. With the method of commission pay per click ( PPC), yielding money from its google method is much more simple and very liquid, different by affiilasi other, obliging we sell something newly get the commission. Google Adsense have brought the new revolution in business internet, this pogram have yielded the millionaire online without having to look for the ordinary big investor such as those which conducted by company of dot com from Silicon valley

What is Google Adwords and Google Adsense ?
Before recognizing more also about Google Adsense, a few beforehand will be commented by Google Adwords representing cikal birth will Google Adsense. Google Adwords advertisement program which on the market google to all owner situs which wish to promote the situsnya, by presenting link situs advertiser in seeking result for the keyword of (certain keyword)
Follow the example of : if we conduct seeking in google with the keyword welding for example, hence besides seeking result, in shares of a quarter on the right will emerge the Sponsored Link / Order the Sponsor
Of course, all advertiser will be imposed by a number of expense depended from popular of keyword selected
But Google realize, though he/she this time become the search engine of first one in world, not all consumer internet in a world of hence google as searcher machine, so that advertisement in google adwords, not yet able to reach entire/all consumer internet, therefore they offer to owner situs to install the advertisement google advertisement of exist in the situs, hence owner situs will get the commission from google, method of commission payment like this ordinary referred by the name of pay per click ( PPC

How many Accepted commission
Commission got to be depended a advertisement placed in our situs. Google xself will place the advertisement as according to content / content situs . Price Pay per Click by xself determined by costly how the keyword esteemed by advertiser Adwords, for example keyword welding possible is merely esteemed 0.5 dollar per click, but keyword insurance for example can be esteemed till 30 dollar per click. referred this high valuable Key words by High Paying Keyword ( HPK). Situs-Situs with the specific topic for the keyword of ( referred certain keyword) situs niche. ( follow the example of the situs niche http://www.welding-engineering.com/ by topic welding
Conceiving if us can make the situs visited 1000 people per day , and assume there 10% clicking advertisement with the commission 1 dollar per click, hence in one day that situs have yielded 100 dollar / day or 3000 dollar per month. kan, much higher from salary of fresh graduate. If only having 10 similar situs, calculate xself its production. In Indonesia xself, have there are some one who reach for the above commission 10.000 dollar per month, which can thousands of dollar have a lot of, and surely which merely hundreds of
In America xself, a lot have got hundreds of thousand even millions of dollar, like situs plentyoffish. com ( couple) or digg.com
Consumer internet, therefore they offer to owner situs to install the advertisement of google adwords their situs with the pattern sharing holder of[is so-called Google Adsense . If there is somebody visiting situs of competitor adsense and click the they are non delivering birth from big company silicon valley ( like yahoo, google, etc), but from home, yes from home with the capital PC which terkoneksi to internet

How to participate The Google Adsense Program
From boldness which I mention above, of course to follow this program, which must our situs to place the advertisement, if trading, situs of shop supposing, and advertisement its merchandise. After having situs with the topic / certain niche ( e.g. education, consultant, farm, etc), we can apply in google.com / adsense , do the registration, later;then google of our mereview situs, if up to standard and accepted, google will give the code html which we can include in our situs. Become the deh… It is very simple !
Eiits… await first, how if which caw ngerti make the situs .. don't worry, for the beginner of make the aja blog ( if this surely a lot have ngerti), blog also can be attached the adsense. For beginner following stages;steps make the blog adsense ( its process [is] caw more than one hour
Determining topic blog to be made ( for example. self development. music, education. etc).
Make blog in blogger.com, why having to blogger, because blogger still have the google, become easier to approve, jka have expert can wear other.
Look for the article about selected topic ( searching of google, a lot of, can be edited, or direct copy the paste but of course by mentioning its source), posting article in blog 10-15 posting, later;then newly apply for for the ikutan of program the adsense via situs google.com / adsense
After accepted, we love account which its contents macam2, among other things report sum up the click and commission which we obtain;get, there also html code which omit which live in the copy paste to our situs. To easy blogger its way banget, omit the tambahin page element, later;then click the add html / javascript, copy-kan adsense code there. Become the deh.
Remark: for the time of approval from google, depended situs, can be direct approve, or one day oppositely; also sometime more.
There are some kinds of type advertisement in google, common/ public but weared by adsense for content and adsense for search supposing sell, ready made shop, fill the shop have there is, now what?… yeah omit the buyer searching, this [is] rather heavy phase and butuh time. our Free;Useless is shop without there is which buy. So-Called buyer that is our visitor situs, or in conceived of by public world online of traffic. More and more our traffic situs, meaning excelsior of advertisement possibility [in] click and more and more commission which we accepted
So for the matter of this, how to improve the traffic to our situs by general there is a lot of way of to get the traffic, one of the example get the free traffic by search engine. Follow the example of to return again to early, if we type the keyword welding in google, there is more than 30 million seeking result (draw 1). Which is likeliest opened by all visitor? yes first page. If our situs appear in the first page; yard will very good, second page; yard or third still its ok, but how if in page;yard 20?… who will be hard .. ha....

(Still About) Adsense

2008-09-19T23:22:00.000-07:00

AdSense for search
A companion to the regular AdSense program, AdSense for search, allows website owners to place Google search boxes on their websites. When a user searches the Internet or the website with the search box, Google shares any advertising revenue it makes from those searches with the website owner. However the publisher is paid only if the advertisements on the page are clicked: AdSense does not pay publishers for mere searches.

AdSense for mobile content
AdSense for mobile content allows publishers to generate earnings from their mobile websites using targeted Google advertisements. Just like AdSense for content, Google matches advertisements to the content of a website — in this case, a mobile website.

XHTML compatibility
As of September 2007, the HTML code for the AdSense search box does not validate as XHTML, and does not follow modern principles of website design because of its use of
non-standard end tags, such as and ,
the attribute checked rather than checked="checked",
presentational attributes other than id, class, or style — for example, bgcolor and align,
a table structure for purely presentational (i.e., non-tabular) purposes,1 and
the font tag.2
1: using a table structure for unintended purposes is strongly recommended against by the W3C[citation needed], but nevertheless does not cause a document to fail validation—there is currently no algorithmic method of determining whether a table is "correctly" used.2: the font tag is deprecated but does not fail validation in any XHTML standard.
Additionally, the AdSense advertisement units use the JavaScript method document.write(), which does not work correctly when rendered with the application/xhtml+xml MIME type. The units also use the iframe HTML tag, which is not validated correctly with the XHTML 1.0 Strict or XHTML 1.0 Transitional DOCTYPEs.
The terms of the AdSense program forbid its affiliates from modifying the code, thus preventing these participants from having valid XHTML websites.
However, a workaround has been found by creating a separate HTML webpage containing only the AdSense advertisement units, and then importing this page into an XHTML webpage with an object tag.[7] This workaround appears to be accepted by Google.[8]

How AdSense works
The webmaster inserts the AdSense JavaScript code into a webpage.
Each time this page is visited, the JavaScript code creates an IFrame with a src attribute set to the page's URL.
For contextual advertisements, Google's servers use a cache of the page to determine a set of high-value keywords. If keywords have been cached already, advertisements are served for those keywords based on the AdWords bidding system. (More details are described in the AdSense patent.)
For site-targeted advertisements, the advertiser chooses the page(s) on which to display advertisements, and pays based on cost per mille (CPM), or the price advertisers choose to pay for every thousand advertisements displayed.[9] [10]
For referrals, Google adds money to the advertiser's account when visitors either download the referred software or subscribe to the referred service.[11] The referral program will be retired in August 2008.[12]
Search advertisements are added to the list of results after the visitor performs a search.
Because the JavaScript is sent to the Web browser when the page is requested, it is possible for other website owners to copy the JavaScript code into their own webpages. To protect against this type of fraud, AdSense customers can specify the pages on which advertisements should be shown. AdSense then ignores clicks from pages other than those specified.

Abuse
Some webmasters create websites tailored to lure searchers from Google and other engines onto their AdSense website to make money from clicks. These "zombie" websites often contain nothing but a large amount of interconnected, automated content (e.g., a directory with content from the Open Directory Project, or scraper websites relying on RSS feeds for content). Possibly the most popular form of such "AdSense farms" are splogs (spam blogs), which are centered around known high-paying keywords. Many of these websites use content from other websites, such as Wikipedia, to attract visitors. These and related approaches are considered to be search engine spam and can be reported to Google.
A Made for AdSense (MFA) website or webpage has little or no content, but is filled with advertisements so that users have no choice but to click on advertisements. Such pages were tolerated in the past, but due to complaints, Google now disables such accounts.
There have also been reports of Trojan horses engineered to produce counterfeit Google advertisements that are formatted to look like legitimate ones. The Trojan downloads itself onto an unsuspecting computer through a webpage and then replaces the original advertisements with its own set of malicious advertisements.[13]

Criticism
Due to concerns about click fraud, Google AdSense has been criticized by some search engine optimization firms as a large source of what Google calls "invalid clicks", in which one company clicks on a rival's search engine advertisements to drive up the other company's costs.[14] Some publishers that have been blocked by Google complain that little justification or transparency was provided. Webmasters who publish AdSense can receive a life-long ban without justification.[citation needed] Google claims they cannot "disclose any specific details" on fraudulent clicks since it may reveal the nature of their proprietary click-fraud monitoring system.[15]
To help prevent click fraud, AdSense publishers can choose from a number of click-tracking programs[citation needed]. These programs display detailed information about the visitors who click on the AdSense advertisements. Publishers can use this to determine whether or not they have been a victim of click fraud. There are a number of commercial tracking scripts available for purchase.
The payment terms for webmasters have also been criticized.[16] Google withholds payment until an account reaches US$100,[17] but many small content providers[citation needed] require a long time—years in many cases—to build up this much AdSense revenue. These pending payments are recorded on Google's balance sheet as "accrued revenue share".[18] At the close of its 2006 fiscal year, the sum of all these small debts amounted to a little over US$370 million, money that Google is able to invest but effectively belongs to webmasters. However, Google will pay all earned revenue greater than US$10 when an AdSense account is closed.
Google recently came under fire when the official Google AdSense Blog showcased the French video website Imineo.com. This website violated Google's AdSense Program Policies by displaying AdSense alongside sexually explicit material.[19] Typically, websites displaying AdSense have been banned from showing such content.

Ref:
en.wikipedia.org

Adsense

2008-09-19T23:17:00.000-07:00

Do you know adsense? Of course !

AdSense is an advertisement serving program run by Google. Website owners can enroll in this program to enable text, image, and more recently, video advertisements on their websites. These advertisements are administered by Google and generate revenue on either a per-click or per-impression basis. Google is also currently beta-testing a cost-per-action based service.

Overview
Google uses its Internet search technology to serve advertisements based on website content, the user's geographical location, and other factors. Those wanting to advertise with Google's targeted advertisement system may enroll through AdWords. AdSense has become a popular method of placing advertising on a website because the advertisements are less intrusive than most banners, and the content of the advertisements is often relevant to the website.
Currently, AdSense uses JavaScript code to incorporate the advertisements into a participating website. If the advertisements are included on a website that has not yet been crawled by the Mediabot, AdSense will temporarily display advertisements for charitable causes, also known as public service announcements (PSAs). (The Mediabot is different from the Googlebot, which maintains Google's search index.)

Many websites use AdSense to monetize their content. AdSense has been particularly important for delivering advertising revenue to small websites that do not have the resources for developing advertising sales programs and salespeople. To fill a website with advertisements that are relevant to the topics discussed, webmasters implement a brief script on the websites' pages. Websites that are content-rich have been very successful with this advertising program, as noted in a number of publisher case studies on the AdSense website.
Some webmasters invest significant effort into maximizing their own AdSense income. They do this in three ways:[citation needed]
They use a wide range of traffic-generating techniques, including but not limited to online advertising.
They build valuable content on their websites that attracts AdSense advertisements, which pay out the most when they are clicked.
They use copy on their websites that encourages visitors to click on advertisements. Note that Google prohibits webmasters from using phrases like "Click on my AdSense ads" to increase click rates. The phrases accepted are "Sponsored Links" and "Advertisements".[citation needed]
The source of all AdSense income is the AdWords program, which in turn has a complex pricing model based on a Vickrey second price auction. AdSense commands an advertiser to submit a sealed bid (i.e., a bid not observable by competitors). Additionally, for any given click received, advertisers only pay one bid increment above the second-highest bid.

History
The underlying technology behind AdSense was derived originally from WordNet, Simpli (a company started by the founder of Wordnet, George A. Miller), and a number of professors and graduate students from Brown University, including James A. Anderson, Jeff Stibel, and Steve Reiss.[1] A variation of this technology utilizing WordNet was developed by Oingo, a small search engine company based in Santa Monica founded in 1998 by Gilad Elbaz and Adam Weissman.[2][3] Oingo changed its name to Applied Semantics in 2001,[4] which was later acquired by Google in April 2003 for US$102 million.[5]

AdSense for Feeds
In May 2005, Google announced a limited-participation beta version of AdSense for Feeds, a version of AdSense that runs on RSS and Atom feeds that have more than 100 active subscribers. According to the Official Google Blog, "advertisers have their ads placed in the most appropriate feed articles; publishers are paid for their original content; readers see relevant advertising—and in the long run, more quality feeds to choose from."[6]
AdSense for Feeds works by inserting images into a feed. When the image is displayed by a RSS reader or Web browser, Google writes the advertising content into the image that it returns. The advertisement content is chosen based on the content of the feed surrounding the image. When the user clicks the image, he or she is redirected to the advertiser's website in the same way as regular AdSense advertisements.
AdSense for Feeds has remained in its beta state until August 15, 2008, when it became available to all AdSense users.

To be continue ....

Google Adsense

2008-09-10T02:17:00.000-07:00

Apa Itu Google AdSense

Bagi Anda yang pemula atau awam dengan dunia internet, tentu bertanya-tanya tentang dua kata ini. Google Adsense.

Secara singkat, Google AdSense adalah layanan iklan yg dimiliki oleh Google, dimana para pemilik situs dapat memasang iklan tersebut di situs2 mereka dan mendapatkan penghasilan tambahan. Iklan yg muncul bermacam-macam jenisnya, bisa berupa teks, gambar, bahkan video; namun yg pasti, semuanya menggunakan sistem kontekstual (contextual), dimana iklan tersebut akan relevan atau sesuai dengan isi halaman dimana iklan tersebut dipasang. Perhatikan contoh gambar berikut:

Seluruh iklan disimpan di server milik Google sendiri, sehingga kita tidak perlu menyediakan ruang khusus di server kita untuk AdSense, ataupun meng-upload file-file tertentu.

Cukup dengan menyisipkan kode JavaScript yg diberikan pada halaman situs kita saja kita sudah dapat menikmati hadirnya iklan AdSense di situs kita.

Bagaimana Kita Mendapatkan Uang?

Seperti disebutkan di atas, dengan memasangkan iklan AdSense di situs mereka, pemilik situs memperoleh kesempatan untuk mendapatkan penghasilan tambahan. Bagaimana caranya?

Tidak sulit. Yg perlu Anda, sebagai pemilik situs, lakukan adalah menunggu (dan berdoa) agar ada pengunjung yg meng-klik iklan2 tersebut. Ya, cukup dengan meng-klik saja, otomatis Anda, sebagai publisher AdSense, akan mendapatkan sejumlah uang yg nilai bagiannya diperhitungkan dari besarnya bid yg telah ditentukan oleh si pemasang iklan (advertisers). Meskipun ada faktor2 lain yg mempengaruhi, secara umum, bagian yg diperoleh publisher adalah 20% dari nilai bid.

Perlu diingat, klik yg dihitung hanyalah klik2 yg dianggap valid. Anda tidak diperbolehkan untuk melakukan klik terhadap iklan milik Anda sendiri atau pun menyuruh orang lain meng-klik iklan Anda. Detil peraturan Google AdSense dapat Anda baca di sini.

Setelah Anda mendaftarkan diri di Google AdSense dan diterima, Anda akan mendapatkan akses ke Member Area Google AdSense. Di situ, selain tersedia tool untuk men-generate kode iklan yg dibutuhkan, juga terdapat halaman Report yg mencantumkan perolehan pendapatan Anda beserta jumlah klik yg didapatkan, jumlah tampilan iklan, dan info2 penting lainnya. Perhatikan gambar berikut:

Bagaimana Pembayarannya?

Pembayaran akan dilakukan 30 hari setelah total pendapatan Anda dalam satu bulan mencapai minimal $100. Jadi apabila bulan Februari ini Anda memperoleh $100, maka penghasilan Anda tersebut akan dikirimkan pada akhir bulan Maret. Untuk Indonesia, pembayaran akan dikirimkan dalam bentuk cek dan Anda dapat memilih untuk menggunakan jasa pos ataupun DHL (Express Delivery) dalam proses pengiriman tersebut.

Jika menggunakan jasa pos, waktu pengiriman biasanya paling cepat adalah 20-25 hari (tergantung lokasi Anda). Sedangkan, jika menggunakan DHL, cek sudah akan Anda terima dalam waktu 2-3 hari kerja. Jangan lupa, Anda biaya sebesar $24 jika Anda memilih menggunakan sistem Express Delivery, dimana biaya tersebut otomatis akan dipotong dari penghasilan kita.

Bagaimana Potensi Penghasilannya?

Tidak terbatas! Banyak publisher AdSense yg telah memperoleh ribuan bahkan puluhan ribu dollar per bulannya. Di Indonesia sendiri, publisher AdSense dengan penghasilan ribuan dollar per bulan sudah bukan hal yg aneh lagi. Sebagian dari mereka dapat Anda baca kisahnya di sini.

Meskipun berpotensi untuk meraih pendapatan yg besar dan bahkan tidak terbatas, berbisnis Google AdSense tidak semudah membalikkan telapak tangan. Semua tetap butuh usaha dan waktu yg mungkin tidak sedikit.

So, tunggu apa lagi? Daftar sekarang (gunakan tombol di bawah ini untuk langsung menuju ke halaman Sign Up) dan mulailah memasuki dunia bisnis internet melalui Google AdSense. Semoga sukses!

Referensi:
www.cosaaaranda.com

Introduce Motherboard

2008-08-30T21:36:00.000-07:00

From Wikipedia, the free encyclopedia

Motherboard
The ASUS CUSL2-C motherboard

A motherboard is the central or primary printed circuit board (PCB) making up a complex electronic system, such as a modern computer. It is also known as a mainboard, baseboard, system board, planar board, or, on Apple computers, a logic board, and is sometimes abbreviated casually as mobo.^[1]

Most motherboards produced today are designed for so-called IBM-compatible computers, which held over 96% of the global personal computer market in 2005.^[2] Motherboards for IBM-compatible computers are specifically covered in the PC motherboard article.

A motherboard, like a backplane, provides the electrical connections by which the other components of the system communicate, but unlike a backplane also contains the central processing unit and other subsystems such as real time clock, and some peripheral interfaces.

A typical desktop computer is built with the microprocessor, main memory, and other essential components on the motherboard. Other components such as external storage, controllers for video display and sound, and peripheral devices are typically attached to the motherboard via edge connectors and cables, although in modern computers it is increasingly common to integrate these "peripherals" into the motherboard.

Components and functions

The 2004 K7VT4A Pro^[3] motherboard by ASRock. The chipset on this board consists of northbridge and southbridge chips.

The motherboard of a typical desktop consists of a large printed circuit board. It holds electronic components and interconnects, as well as physical connectors (sockets, slots, and headers) into which other computer components may be inserted or attached.

Most motherboards include, at a minimum:

sockets (or slots) in which one or more microprocessors (CPUs) are installed^[4]
slots into which the system's main memory is installed (typically in the form of DIMM modules containing DRAM chips)
a chipset which forms an interface between the CPU's front-side bus, main memory, and peripheral buses
non-volatile memory chips (usually Flash ROM in modern motherboards) containing the system's firmware or BIOS
a clock generator which produces the system clock signal to synchronize the various components
slots for expansion cards (these interface to the system via the buses supported by the chipset)
power connectors and circuits, which receive electrical power from the computer power supply and distribute it to the CPU, chipset, main memory, and expansion cards.^[5]

The Octek Jaguar V motherboard from 1993.^[6] This board has 6 ISA slots but few onboard peripherals, as evidenced by the lack of external connectors.

Additionally, nearly all motherboards include logic and connectors to support commonly-used input devices, such as PS/2 connectors for a mouse and keyboard. Early personal computers such as the Apple II or IBM PC included only this minimal peripheral support on the motherboard. Occasionally video interface hardware was also integrated into the motherboard; for example on the Apple II, and rarely on IBM-compatible computers such as the IBM PC Jr. Additional peripherals such as disk controllers and serial ports were provided as expansion cards.

Given the high thermal design power of high-speed computer CPUs and components, modern motherboards nearly always include heatsinks and mounting points for fans to dissipate excess heat.

Integrated peripherals

Diagram of a modern motherboard, which supports many on-board peripheral functions as well as several expansion slots.

With the steadily declining costs and size of integrated circuits, it is now possible to include support for many peripherals on the motherboard. By combining many functions on one PCB, the physical size and total cost of the system may be reduced; highly-integrated motherboards are thus especially popular in small form factor and budget computers.

For example, the ECS RS485M-M,^[7] a typical modern budget motherboard for computers based on AMD processors, has on-board support for a very large range of peripherals:

disk controllers for a floppy disk drive, up to 2 PATA drives, and up to 6 SATA drives (including RAID 0/1 support)
integrated ATI Radeon graphics controller supporting 2D and 3D graphics, with VGA and TV output
integrated sound card supporting 8-channel (7.1) audio and S/PDIF output
fast Ethernet network controller for 10/100 Mbit networking
USB 2.0 controller supporting up to 12 USB ports
IrDA controller for infrared data communication (e.g. with an IrDA enabled Cellular Phone or Printer)
temperature, voltage, and fan-speed sensors that allow software to monitor the health of computer components

Expansion cards to support all of these functions would have cost hundreds of dollars even a decade ago, however as of April 2007 such highly-integrated motherboards are available for as little as $30 in the USA.

Temperature and reliability

Motherboards are generally air cooled with heat sinks often mounted on larger chips, such as the northbridge, in modern motherboards. Passive cooling, or a single fan mounted on the power supply, was sufficient for many desktop computer CPUs until the late 1990s; since then, most have required CPU fans mounted on their heatsinks, due to rising clock speeds and power consumption. Most motherboards have connectors for additional case fans as well. Newer motherboards have integrated temperature sensors to detect motherboard and CPU temperatures, and controllable fan connectors which the BIOS or operating system can use to regulate fan speed.

Some small form factor computers and home theater PCs designed for quiet and energy-efficient operation boast fan-less designs. This typically requires the use of a low-power CPU, as well as careful layout of the motherboard and other components to allow for heat sink placement.

A 2003 study^[8] found that some spurious computer crashes and general reliability issues, ranging from screen image distortions to I/O read/write errors, can be attributed not to software or peripheral hardware but to aging capacitors on PC motherboards. Ultimately this was shown to be the result of a faulty electrolyte formulation.^[9]

For more information on premature capacitor failure on PC motherboards, see capacitor plague.

Motherboards use electrolytic capacitors to filter the DC power distributed around the board. These capacitors age at a temperature-dependent rate, as their water based electrolytes slowly evaporate. This can lead to loss of capacitance and subsequent motherboard malfunctions due to voltage instabilities. While most capacitors are rated for 2000 hours of operation at 105 °C,^[10] their expected design life roughly doubles for every 10 °C below this. At 45 °C a lifetime of 15 years can be expected. This appears reasonable for a computer motherboard, however many manufacturers have delivered substandard capacitors, which significantly reduce this life expectancy. Inadequate case cooling and elevated temperatures easily exacerbate this problem. It is possible, but tedious and time-consuming, to find and replace failed capacitors on PC motherboards; it is less expensive to buy a new motherboard than to pay for such a repair.

History

Prior to the advent of the microprocessor, a computer was usually built in a card-cage case or mainframe with components connected by a backplane consisting of a set of slots themselves connected with wires; in very old designs the wires were discrete connections between card connector pins, but printed-circuit boards soon became the standard practice. The central processing unit, memory and peripherals were housed on individual printed circuit boards which plugged into the backplane.

During the late 1980s and 1990s, it became economical to move an increasing number of peripheral functions onto the motherboard (see above). In the late 1980s, motherboards began to include single ICs (called Super I/O chips) capable of supporting a set of low-speed peripherals: keyboard, mouse, floppy disk drive, serial ports, and parallel ports. As of the late 1990s, many personal computer motherboards support a full range of audio, video, storage, and networking functions without the need for any expansion cards at all; higher-end systems for 3D gaming and computer graphics typically retain only the graphics card as a separate component.

The early pioneers of motherboard manufacturing were Micronics, Mylex, AMI, DTK, Hauppauge, Orchid Technology, Elitegroup, DFI, and a number of Taiwan-based manufacturers.

Popular personal computers such as the Apple II and IBM PC had published schematic diagrams and other documentation which permitted rapid reverse-engineering and third-party replacement motherboards. Usually intended for building new computers compatible with the exemplars, many motherboards offered additional performance or other features and were used to upgrade the manufacturer's original equipment.

Bootstrapping using the BIOS

Main article: booting

Motherboards contain some non-volatile memory to initialize the system and load an operating system from some external peripheral device. Microcomputers such as the Apple II and IBM PC used read-only memory chips, mounted in sockets on the motherboard. At power up the central processor would load its program counter with the address of the boot ROM and start executing ROM instructions displaying system information on the screen and running memory checks, which would in turn start loading memory from an external or peripheral device (disk drive) if one isn't available then the computer can perform tasks from other memory stores or displays an error message depending on the model and design of the computer and version of the bios.

Most modern motherboard designs use a BIOS, stored in a EEPROM chip soldered to the motherboard, to bootstrap the motherboard. (Socketed BIOS chips are widely used, also.) By booting the motherboard, the memory, circuitry, and peripherals are tested and configured. This process is known as a Power On Self Test or POST. Errors during POST result in POST error codes, ranging from simple audible beeps from the speaker to complex diagnostic messages displayed on the video monitor.

The BIOS often requires configuration settings to be stored on the motherboard. Since configuration settings must be easily edited, these settings are often stored in non-volatile RAM (NVRAM) rather than in some sort of read-only memory (ROM). When a user makes configuration changes or alters the date and time of the computer, this small NVRAM circuit stores the data. Typically, a small, long-lasting battery (e.g. a lithium coin cell CR2032) is used to keep the NVRAM "refreshed" for many years. Therefore, a failing battery on a motherboard will produce the symptoms of a computer that cannot determine the correct date and time, nor remember what hardware configuration the user has selected. The BIOS itself is unaffected by the status of the battery.

When IBM first introduced the PC in the 1980s, imitations were quite common. (The physical parts which made up the motherboard were trivial to acquire.) However, the imitations were never successful until the IBM ROM BIOS was legally copied.^[11] To understand why copying the BIOS was an important step, consider that the BIOS contained vital instructions which interacted with peripherals. Without these software instructions in the BIOS, a PC would not function properly. (In most modern computer operating systems, the BIOS is bypassed for most hardware functions, but in the 1980s, the BIOS served many vital low-level functions.)

So when Compaq Computer Corp. spent US$1 million to clone the IBM BIOS using reverse engineering, they became an elite computer manufacturer of IBM PC Clones. Phoenix Technology soon matched their feat and began reselling BIOSes to other clone makers.^[12] It has been noted that Microsoft was more than happy to license the operating system (DOS), and IBM was more than happy to sue companies^[13] that violated the copyright of their BIOS. But by documenting and publicizing the reverse engineering of the BIOS, Compaq and Phoenix were legally competing with IBM using their own copyrighted BIOS.

Once the bootstrapping of the computer's peripherals are complete, the BIOS will normally pass control to another set of instructions stored on a bootable device.

Devices which are normally used to boot a computer:

floppy drive
network controller
CD-ROM drive
DVD-ROM drive
SCSI hard drive
IDE, EIDE, or SATA hard drive
External USB memory storage device

Any of the above devices can be stored with machine code instructions to load an operating system or a program.

Form factors

Main article: Comparison of computer form factors

Motherboards are produced in a variety of sizes and shapes ("form factors"), some of which are specific to individual computer manufacturers. However, the motherboards used in IBM-compatible commodity computers have been standardized to fit various case sizes. As of 2007, most desktop computer motherboards use one of these standard form factors—even those found in Macintosh and Sun computers which have not traditionally been built from commodity components.

Laptop computers generally use highly integrated, miniaturized, and customized motherboards. This is one of the reasons that laptop computers are difficult to upgrade and expensive to repair. Often the failure of one laptop component requires the replacement of the entire motherboard, which is usually more expensive than a desktop motherboard due to the large number of integrated components.

Dot Matrix Printer

2008-08-29T00:57:00.000-07:00

From Wikipedia, the free encyclopedia

Typical output from a dot matrix printer operating in draft mode. This entire image represents an area of printer output approximately 4.5 cm x 1.5cm (1.75 x 0.6 inches) in size.

Dot matrix printer or impact matrix printer refers to a type of computer printer with a print head that runs back and forth on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper, much like a typewriter. Unlike a typewriter or daisy wheel printer, letters are drawn out of a dot matrix, and thus, varied fonts and arbitrary graphics can be produced. Because the printing involves mechanical pressure, these printers can create carbon copies and carbonless copies.

Each dot is produced by a tiny metal rod, also called a "wire" or "pin", which is driven forward by the power of a tiny electromagnet or solenoid, either directly or through small levers (pawls). Facing the ribbon and the paper is a small guide plate (often made of an artificial jewel such as sapphire or ruby [1]) pierced with holes to serve as guides for the pins. The moving portion of the printer is called the print head, and when running the printer as a generic text device generally prints one line of text at a time. Most dot matrix printers have a single vertical line of dot-making equipment on their print heads; others have a few interleaved rows in order to improve dot density.

These machines can be highly durable. When they do wear out, it is generally due to ink invading the guide plate of the print head, causing grit to adhere to it; this grit slowly causes the channels in the guide plate to wear from circles into ovals or slots, providing less and less accurate guidance to the printing wires. Eventually, even with tungsten blocks and titanium pawls, the printing becomes too unclear to read.

Although nearly all inkjet, thermal, and laser printers produce dot matrices, in common parlance these are seldom called "dot matrix" printers, to avoid confusion with dot matrix impact printers.

Early Dot Matrix Printers

The LA30 was a 30 character/second dot matrix printer introduced in 1970 by Digital Equipment Corporation of Maynard, Massachusetts. It printed 80 columns of uppercase-only 5x7 dot matrix characters across a unique-sized paper. The printhead was driven by a stepper motor and the paper was advanced by a somewhat-unreliable and definitely noisy solenoid ratchet drive. The LA30 was available with both a parallel interface and a serial interface; however, the serial LA30 required the use of fill characters during the carriage-return operation.

The LA30 was followed in 1974 by the LA36, which achieved far greater commercial success, becoming for a time the standard dot matrix computer terminal. The LA36 used the same print head as the LA30 but could print on forms of any width up to 132 columns of mixed-case output on standard green bar fanfold paper. The carriage was moved by a much-more-capable servo drive using a dc motor and an optical encoder/tachometer. The paper was moved by a stepper motor. The LA36 was only available with a serial interface but unlike the earlier LA30, no fill characters were required. This was possible because, while the printer never communicated at faster than 30 characters per second, the mechanism was actually capable of printing at 60 characters per second. During the carriage return period, characters were buffered for subsequent printing at full speed during a catch-up period. The two-tone buzz produced by 60 character-per-second catch-up printing followed by 30 character-per-second ordinary printing was a distinctive feature of the LA36.

Digital then broadened the basic LA36 line onto a wide variety of dot matrix printers including:

LA180 -- 180 c/s line printer
LS120 -- 120 c/s terminal
LA120 -- 180 c/s advanced terminal
LA34 -- Cost-reduced terminal
LA38 -- An LA34 with more features
LA12 -- A portable terminal

In 1970, Centronics (then of Hudson, New Hampshire) introduced a dot matrix printer, the Centronics 101. The search for a reliable printer mechanism led it to develop a relationship with Brother Industries, Ltd. of Japan, and the sale of Centronics-badged Brother printer mechanisms equipped with a Centronics print head and Centronics electronics. Unlike Digital, Centronics concentrated on the low-end line printer marketplace with their distinctive units. In the process, they designed the parallel electrical interface that was to become standard on most dot matrix printers (indeed, most printers in general) until it started to be replaced by the Universal Serial Bus (USB) in the late 1990s.

Dot matrix features

As with any technology product, feature-sets for dot-matrix impact printers vary by price, intended market, and year of introduction.

Industrial market

Industrial-market printers are designed for high-volume printing and offer construction, feed paths, and carriage configurations suited for this task. The carriage assembly typically houses multiple printheads, permitting rapid printing of the entire paper-width with only a partial carriage displacement. Industrial printers are often cabinet-sized, with their own housing for blank paper, the printer, and printed output. Suppliers of industrial impact printers include Mannesmann-Tally, PSi, Genicom and Printronix.

Personal computer market

A Tandy 1000 HX with a Tandy DMP-133 dot-matrix printer.

The 1980s saw a wide variety of printers from many different manufacturers. Nearly all consumer printers are desktop sized. Common features included:

alphanumeric mode (text) - ASCII/ANSI character printing mode, encoded as 1 byte per printed character. Early IBM PC printers had limited typeface definitions, later printers had fully ANSI-compliant typeface definitions. Standard on all dot-matrix printers. (Note: 'Windows-only' printers no longer support text mode printing from MS-DOS.)

bitmap mode (graphics) - freeform bitmap printing. Controller transcribed any host-provided bitmap sequence. Standard on all but the earliest dot-matrix models.

boldface (text) - Usually implemented by printing selected text segment in printer's double-density mode. (For NLQ fonts which already used double-density mode, the printer controller digitally 'widened' the typeface bitmap.)

color printing (text+graphics)- multi-color output, generally achieved with multiple printhead passes. Required a color ribbon to be installed.

condensed cpi (text) - characters per inch, standard-sized text was 10cpi (or 80 columns for letter-width paper.) Many printers offered condensed text modes of 12cpi, 15cpi, 17cpi, and 20cpi. If supported in NLQ mode, the condensed typefaces generally used extra storage (ROM) in the printer controller to hold different versions of the typeface. (Early printers limited NLQ mode to 10cpi or 12cpi.)

doublestrike (text) - double printing (two-pass) of a selected text segment. Sometimes used to simulate boldface or cheap, poor-quality NLQ.

downloadable font (text) - ability to accept and store a user-defined typeface. The user-downloaded typeface was downloaded into printer's onboard RAM, where it becomes available to subsequent (alphanumeric) text print jobs. First offered on the 9-pin Epson FX-80. Later high-end 24-pin printers supported 2 or more simultaneous user fonts, allowing a print job to use any combination of user or built-in typefaces.

draft (text) - high-speed print mode, characters were formed with openly spaced dots. Some models had multiple draft modes with differing speed and dot density. Many printers could print draft mode text bidirectionally - every other line was printed backwards, so that no time was lost for moving back the print head to the start of the next line.

italics (text) - built-in italics capability. Printer controller created the effect through digital processing of the typeface.

NLQ (text) - Near Letter Quality, ASCII typeface with improved darkness and readability. Generally slower to print, especially on 9-pin printers, which used two passes of the print head and usually turned off bidirectional printing to achieve this quality. (Available on 24-pin printers and later model 9-pin printers.)

outline (text) - printed selected text segment in a hollowed outline of the typeface. Printer controller created the effect through digital processing of the typeface. Found on a handful of late-model 24-pin printers (such as Epson LQ-570/870/1070.)

proportional-space font (text) - non-uniform (horizontal) spacing between characters. Some models only allowed PS in conjunction with specific typefaces. Word processing programs needed to know the width of every character used by the printer in this mode to determine where to break lines; thus software support was often limited.

quiet-mode (text+graphics) - reduced the printhead's acoustic noise during printing. Generally reduced the speed of printing.

scalable font (text) - allowed user control of a font's printed-size (continuously variable point-size.) Unlike the traditional bitmap representation of typeface data, scalable typefaces used a vector-based definition. Found on a handful of late-model 24-pin printers (such as Epson LQ-570/870.)

shadow (text) - added a shadow to a selected text segment. Printer controller created the effect through digital processing of the typeface. Found on a handful of late-model 24-pin printers (such as Epson LQ-570/870/1070.)

subscript/superscript (text) - built-in typeface for simulating raised and lowered letters. (Usually implemented as a separate typeface.)

typeface (text) - the typeface is the bitmap (image) definition of a font. Common printer typefaces were Courier, Roman, Serif, and Sans Serif. Early and low-end printers offered a single typeface. High-end and later models offered 2 or more distinct typefaces, as well as user-downloading of custom typefaces.

wide-carriage (carriage size) - could print to wider (132 column) paper. Standard-carriage printers printed on letter-width (8.5") paper.

dot-density (printhead and controller) - "dot matrix resolution" for 9-pin printers: Vertical is 72dpi, horizontal (dpi):60, 66, 72, 80, 96, 120, 132, 144, 160, 180, 240. For 24-pin printers (in native 24-pin mode), Vertical is 180dpi, horizontal (dpi): 60, 90, 120, 180, 240, 360. Many models could achieve higher vertical-density through fractional linefeeds (1/144" or 1/216" for 9-pin, 1/360" for 24-pin), for a maximum-rating of 240x216, or 360x360.
9-pin (printhead configuration) - the standard printhead config until the introduction of 24-pin printers. Later models offered dot density up to 240dpi (horizontal.)

18-pin, 27-pin (printhead configuration) - uncommon in consumer market.

24-pin (printhead configuration) - square pixel for high bitmap resolution (180x180dpi standard), faster and higher-quality NLQ mode. Later models offered dot density up to 360dpi (horizontal.)

Dot matrix usage

Personal Computers

An Epson MX-80

In the 1970s and 1980s, dot matrix impact printers were generally considered the best combination of expense and versatility, and until the 1990s they were by far the most common form of printer used with personal computers.

The Epson MX-80 was the groundbreaking model that sparked the initial popularity of impact printers in the personal computer market. The MX-80 combined affordability with solid text output (for its time.) Early impact printers (including the MX) were notoriously loud during operation, a result of the hammer-like mechanism in the print head. Furthermore, the MX-80's low dot density (60dpi horizontal, 72dpi vertical) produced printouts of a distinctive "computerized" quality. When compared to the crisp typewriter quality of a daisy-wheel printer, the dot-matrix printer's legibility appeared especially bad. In office applications, output quality was a serious issue, as the dot-matrix text's readability would rapidly degrade with each photocopy generation.

Initially, third-party software (such as Bradford) printer enhancement program, offered a quick fix to the quality issue. The software utilized a variety of software techniques to increase print quality; general strategies were doublestrike (print each line twice), and double-density mode (slow the print head to allow denser and more precise dot placement.) Such add-on software was inconvenient to use, because it required the user to remember to run the enhancement program before each printer session (to activate the enhancement mode.) Furthermore, they were not compatible with all programs.

Early personal computer software focused on the processing of text, but as graphics displays became ubiquitous throughout the personal computer world, users wanted to print both text and images. Ironically, whereas the daisy-wheel printer and pen-plotter struggled to reproduce bitmap images, the first dot-matrix impact printers (including the MX-80) lacked the ability to print computer-generated images. Yet the dot-matrix print head was well-suited to this task, and the capability quickly became a standard feature on all PC-oriented dot-matrix printers.

Progressive hardware improvements to impact printers boosted the carriage speed, added more (typeface) font options, increased the dot density (from 60dpi up to 240dpi), and added pseudo-color printing. Faster carriage speeds meant faster (and sometimes louder) printing. Additional typefaces allowed the user to vary the text appearance of printouts. Proportional-spaced fonts allowed the printer to imitate the non-uniform character widths of a typesetter. Increased dot density allowed for more detailed, darker printouts. The impact pins of the printhead were constrained to a minimum size (for structural durability), and dot densities above 100dpi merely caused adjacent dots to overlap. While the pin diameter placed a lower limit on the smallest reproducible graphic detail, manufacturers were able to use higher dot density to great effect in improving text quality.

Several dot-matrix impact printers (such as the Epson FX series) offered 'user-downloadable fonts'. This gave the user the flexibility to print with different typefaces. PC software downloaded a user-defined fontset into the printer's memory, replacing the built-in typeface with the user's selection. Any subsequent text printout would use the downloaded font, until the printer was powered off or soft-reset. Several third-party programs were developed to allow easier management of this capability. With a supported word-processor program (such as WordPerfect 5.1), the user could embed up to 2 NLQ custom typefaces in addition to the printer's built-in (ROM) typefaces. (The later rise of WYSIWYG software philosophy rendered downloaded fonts obsolete.)

Single-strike and Multi-strike ribbons were an attempt to address issues in the ribbon's ink quality. Standard printer ribbons used the same principles as typewriter ribbons. The printer would be at its darkest with a newly installed ribbon cartridge, but would gradually grow fainter with each successive printout. The variation in darkness over the ribbon cartridge's lifetime prompted the introduction of alternative ribbon formulations. Single-strike ribbons used a carbon-like substance in typewriter ribbons transfer. As the ribbon was only usable for a single loop (rated in terms of 'character count'), the blackness was of consistent, outstanding darkness. Multi-strike ribbons gave an increase in ribbon life, at the expense of quality.

Pseudo-Color

Several manufacturers implemented color dot-matrix impact printing through a multi-color ribbon. Color was achieved through a multi-pass composite printing process. During each pass, the print head struck a different section of the ribbon (one primary color.) For a 4-color ribbon, each printed line of output required a total of 4 passes. In some color printers, such as the Apple ImageWriter II, the printer moved the ribbon relative to the fixed print head assembly. In other models, the print head was tilted against a stationary ribbon.

Due to their poor color quality and increased operating expense, color impact models never replaced their monochrome counterparts.^{[citation needed]} As the color ribbon was used in the printer, the black ink section would gradually contaminate the other 3 colors, changing the consistency of printouts over the life of the ribbon. Hence, the color dot-matrix was suitable for abstract illustrations and piecharts, but not for photo-realistic reproduction. Dot-matrix thermal-transfer printers offered more consistent color quality, but consumed printer film, still more expensive. Color printing in the home would only become ubiquitous much later, with the ink-jet printer.The speed is usually 30-550 cps

Near Letter Quality (NLQ)

Text quality was a recurring issue with dot-matrix printers. Near Letter Quality mode endowed dot-matrix printers with a simulated typewriter-like quality. By using multiple passes of the carriage, and higher dot density, the printer could increase the effective resolution. For example, the Epson FX-86 could achieve a theoretical addressable dot-grid of 240 by 216 dots/inch using a print head with a vertical dot density of only 72 dots/inch, by making multiple passes of the print head for each line. For 240 by 144 dots/inch, the print head would make one pass, printing 240 by 72 dots/inch, then the printer would advance the paper by half of the vertical dot pitch (1/144 inch), then the print head would make a second pass. For 240 by 216 dots/inch, the print head would make three passes with smaller paper movement (1/3 vertical dot pitch, or 1/216 inch) between the passes. To cut hardware costs, some manufacturers merely used a double strike (doubly printing each line) to increase the printed text's boldness, resulting in bolder but still jagged text. In all cases, NLQ mode incurred a severe speed penalty. Not surprisingly, all printers retained one or more 'draft' modes for high-speed printing.

NLQ became a standard feature on all dot-matrix printers. While NLQ was well received in the IBM PC market, the Apple Macintosh market did not use NLQ mode at all, as it did not rely on the printer's own fonts. Mac word-processing applications used fonts stored in the computer. For non-PostScript (raster) printers, the final raster image was produced by the computer and sent to the printer, which meant dot-matrix printers on the Mac platform exclusively used raster ("graphics") printing mode. For near-letter-quality output, the Mac would simply double the resolution used by the printer, to 144 dpi, and use a screen font twice the point size desired. Since the Mac's screen resolution (72 dpi) was exactly half of the ImageWriter's maximum, this worked perfectly, creating text at exactly the desired size. The Mac's WYSIWYG philosophy foreshadowed the direction the PC market would later follow.

24-pin printers

By the mid 1980s, manufacturers had increased the pincount of the impact printhead from 9 pins to 18, or 24. (At 27 pins, the Apple ImageWriter LQ held the record for consumer market.) The increased pin-count permitted superior print-quality which was necessary for success in Asian markets to print legible CJK characters. In the PC market, nearly all 9-pin printers printed at a defacto-standard vertical pitch of 9/72 inch (per printhead pass.) Epson's 24-pin LQ-series rose to become the new de-facto standard, at 24/180 inch (per pass.) Not only could a 24-pin printer lay down a denser dot-pattern in a single-pass, it could simultaneously cover a larger area.

Compared to the older 9-pin models, a new 24-pin impact printer not only produced better-looking NLQ text, it printed the page quicker (largely due to the 24-pin's ability to print NLQ with a single pass.) 24-pin printers repeated this feat in bitmap graphics mode, producing higher-quality graphics in reduced time. While the text-quality of a 24-pin was still visibly inferior to a true letter-quality printer—the daisy wheel or laser-printer, the typical 24-pin impact printer outpaced most daisy-wheel models.

As manufacturing costs declined, 24-pin printers gradually replaced 9-pin printers. 24-pin printers reached a dot-density of 360x360 dpi, a marketing figure aimed at misleading potential buyers of competing ink-jet and laser-printers. 24-pin NLQ fonts generally used a dot-density of 360x180, the highest allowable with single-pass printing. Multipass NLQ was abandoned, as most manufacturers felt the marginal quality improvement did not justify the tradeoff in speed. Most 24-pin printers offered 2 or more NLQ typefaces, but the rise of WYSIWYG software and GUI environments such as Microsoft Windows ended the usefulness of NLQ.

Use of dot matrix printers today

The desktop impact printer was gradually replaced by the inkjet printer. When Hewlett-Packard's patents expired on steam-propelled photolithographically-produced ink-jet heads, the inkjet mechanism became available to the printer industry. The inkjet was superior in nearly all respects: comparatively quiet operation, faster print speed, and output quality almost as good as a laser printer. By the mid-1990s, inkjet technology had surpassed dot-matrix in the mainstream market.

As of 2005, dot matrix impact technology remains in use in devices such as cash registers, ATM, and many other point-of-sales terminals. Thermal printing is gradually supplanting them in these applications. Full-size dot-matrix impact printers are still used to print multi-part stationery, for example at bank tellers, and other applications where use of tractor feed paper is desirable such as data logging and aviation. Some are even fitted with USB interfaces as standard to aid connection to modern legacy-free computers. Dot matrix printers are also more tolerant of the hot and dirty operating conditions found in many industrial settings. The simplicity and durability of the design allows users who are not "computer literate" to easily perform routine tasks such as changing ribbons and correcting paper jams.

Some companies, such as WeP Peripherals [2], Epson [3], Okidata [4], Olivetti [5], Lexmark [6], and TallyGenicom [7], still produce serial and line printers. Today, a new dot matrix printer actually costs more than most inkjet printers and some entry level laser printers. However, not much should be read into this price difference as the printing costs for inkjet and laser printers are a great deal higher than for dot matrix printers, and the inkjet/laser printer manufacturers effectively use their monopoly over arbitrarily priced printer cartridges to subsidise the initial cost of the printer itself (see Inkjet printer -> Underlying business model). Dot matrix ribbons are a commodity and are not monopolised by the printer manufacturers themselves.

Dot matrix printers are the dominant type of printer in small firms and offices in some parts of India.

Advantages and Disadvantages

Advantages

Dot matrix printers, like any impact printer, can print on multi-part stationery or make carbon copies. Impact printers have one of the lowest printing costs per page. As the ink is running out, the printout gradually fades rather than suddenly stopping partway through a job. They are able to use continuous paper rather than requiring individual sheets, making them useful for data logging. They are good, reliable workhorses ideal for use in situations where printed content is more important than quality. The ink ribbon also does not easily dry out, including both the ribbon stored in the casing as well as the portion that is stretched in front of the print head; this unique property allows the dot-matrix printer to be used in environments where printer duty can be rare, for instance, as with a Fire Alarm Control Panel's output.

Disadvantages

Impact printers are usually noisy, to the extent that sound dampening enclosures are available for use in quiet environments. They can only print low resolution graphics, with limited color performance, limited quality and comparatively low speed. While they support fanfold paper with tractor holes, single-sheet paper usually has to be wound in and aligned by hand, which is relatively inconvenient and time-consuming. While far better suited to printing on labels than a laser printer or an inkjet printer, they are prone to bent pins (and therefore a destroyed printhead) caused by printing a character half-on and half-off the label; for text-only labels (ie. mailing labels), a daisy wheel printer offers most of the advantages of a dot matrix, with better print quality and a lesser chance of being damaged.

Future of Dot-Matrix Printers

The main use of Dot-Matrix Printers are in areas of intensive transaction-processing systems that churn out quite a lot of printing. Many companies who might have started off with dot-matrix printers are not so easily convinced to go for printers based on other technologies because of the speed advantage that they have with dot-matrix printers.

Let The Dual-Core Revolution Begin

2008-08-27T21:43:00.000-07:00

First Intel Dual-Core Processors Delivered Ahead Of Schedule

In April, Intel Delivered its first dual-core desktop-based platform: the top-of-the-line Intel Pentium Extreme Edition 840 and the 955X Express chipset. At about the same time, AMD released its dual-core Opterons.

Dual-core processors are just what they sound like: two or more independent, full-execution CPU cores within a single physical processor. Although the memory controller and bus are shared, there are two independent pipelines with two sets of instructions being carried out simultaneously and two caches to keep more of the necessary processing data on the processor for faster access.

Combined with the Intel 955X Express Chipset, the Pentium EE 840 supports Intel’s Hyper-Threading technology, which allows each of the two processor cores to function as two logical processors. With two actual and two logical processors, four software threads can be processed in parallel. Each logical processor has its own architecture state with its own set of general-purpose registers and control registers to provide increased system responsiveness in multitasking environments and to provide headroom for the next generation of multithreaded applications.

Evaluating Dual-Core Benefits
So how can dual-core processing help in the day-to-day operations of your data center? Intel’s new dual-core processors will certainly offer immediate performance benefits for specialized users. The dual-core architecture allows users to multitask more effectively than ever before and run the most demanding desktop applications while maintaining system responsiveness. IT departments can deploy desktop background services that make their environments more secure, efficient, and manageable, while minimizing the impact on end-user productivity.
Business users who open multiple apps at once and regularly perform several simultaneous operations will benefit from the dual-core Pentium EE 840, especially when the tasks are computationally demanding.

But evaluating these benefits for decision-making purposes is not always straightforward. To begin with, dual-core processors will not be twice as fast as a single-core processor, nor will it be as fast as a system with two separate processors. Performance numbers will fall in between, depending largely on the software application. Also dual-core performance cannot be measured adequately by the traditional standards of clock speed and cache size. In fact, the dual-core clock speeds will probably be lower than those of the fastest Pentium 4 chips available. However, two slower cores can do more work than a single faster core and can reduce heat production compared to an equivalent single-core device, resulting in a quieter and more reliable machine. On the other hand, dual-core systems may not perform as well as their single-core counter-parts when processing single-thread applications that use only one of the two cores. Keep in mind that most software applications are still single-threaded.

The enterprise world (servers and workstations) will benefit first from dual-core and multithreading technology. Many applications in this area, including most enterprise-level server applications from Oracle and SAP, are already multithreaded. Note that some vendors, notably Oracle and Microsoft, will require one license for each core on the processor. In some cases this results in a significant price boost.

In the desktop world, the only business area that sees immediate benefit is content creation, including image encoding and processing, automation, simulation, and publishing applications. In this area, multithreaded programs such as Adobe Photoshop are much faster on a dual-core system than on its single-core counterpart. The bigger the processing job, the greater the jump in performance.

But once again, most desktop business applications are not written to use multithreading because the design of spreadsheet, word processing, and other productivity software has not been impacted by available processing power. And if the software cannot “see” the second processor, it cannot benefit from it. Indeed, in single-threaded applications, the fastest single-core chips may outperform their dual-core counterparts.

Time To Transition?
Sooner or later, your business will be operating in a multithreaded, multi-processor world. Industry analysts agree that the Pentium D and the Pentium Extreme Edition 840 dual-core processors, with their corresponding 945 and 955X chipsets, represent Intel’s next strategic platform. Businesses must eventually move to the new platform if they want to implement the advanced technologies embodied there. But when should you transition?

If you see a productivity increase based on dual-core processing and the increase promises a meaningful business benefit, you may want to move quickly. In this situation, Intel recommends considering early deployment of selected dual-core or multicore systems. Full-scale deployment would follow, beginning in Q1 2006. For most businesses, however, there is no rush. By this time next year, the new platform will be widely available and significantly enhanced. Why not wait and check prices against processing power then? The introduction of dual- or multiprocessing is a major transition that will require careful planning and management.

The Competition Heats Up
On the enterprise side, AMD has released its dual-core 64-bit Opteron processor. Intel will introduce a dual-core version of its Itanium server chip later this year and is expected to introduce dual-core Xeon processors in 2006. For desktops, AMD plans to release a dual-core 64-bit Athlon in June. Both AMD and Intel are expected to add dual-core technology to their mobile chip lines by next year. The range of clock speeds and the cache sizes in the competing product lines are generally comparable. Note that some AMD processors are being shipped for use in existing motherboards, occupying the same socket as their single-core predecessors.

Original article by Alan Petraske

Processors, Chipsets & Memory

2008-08-27T21:24:00.000-07:00

Semiconductors Rule

Each week, MarketWatch gives you a quick look at what’s happening in a particular product market so you can make better decisions for your company. We interview industry analysts, product manufacturers, and other experts and combine their comments with the latest statistics and market outlooks for a well-rounded perspective. This week’s focus is on processors, chipsets, and memory.

It’s a semiconductor universe to say the least, and things seem all over the map at the moment. Right now, memory pricing is down, processors are seeing dual-core on the table, and chipsets are moving into the next generation, minus the price hikes. Gartner is predicting a 3.4% growth in semiconductor revenue at $227.6 billion in 2005 (up from $220 billion in 2004), but this comes after a 23.9% jump in 2004. The research firm says to take heart, however, as growth rates climb by 2.1% in 2006, 10% in 2007, and 15% in 2008, when the industry will see $300 billion in sales. Let’s take a look at the semiconductor marketplace as it relates to processors, chipsets, and memory.

Processors Although this time of year isn’t the best for processor market details, it’s still safe to say it’s dual-core all the way. AMD and Intel have both recently revealed their first dual-core processing systems. AMD jumped into the server market with three Opteron 800 series processors, and Intel countered into the dual-core desktop market with the Pentium D and the Pentium Extreme Edition CPUs. Intel's Pentium Extreme Edition 840 dual-core chip will run at 3.2GHz and feature 1MB of Level 2 cache for each core.It should cost $999. AMD’s Opteron 800 series processors are for use in four or more socket servers and are AMD’s most expensive. (AMD’s cheapest dual-core server chips will cost as much as the high-end single-core models.)

Bill Kirby, director of platform marketing at Intel, paves the road ahead for dual-core on Intel's behalf. "Intel will ramp this user-valued capability very quickly through 2006, and we expect to exit 2006 shipping more than 70% dual-core processors in the desktop performance (Pentium) and mobile performance (Pentium) segments, and greater than 85% dual-core in the server segment.” Kirby says specifically from an IT perspective, the company believes dual-core will continue to enable IT to enhance the management and protection capabilities without impacting user productivity.

Chipsets

With the release of the nForce4 SLI Intel edition, it appears as though NVIDIA is the chipset maker to follow in 2005. NVIDIA’s Intel chipset supports DDR2 and is the first product from NVIDIA for the Intel market. The nForce4 only supports DDR2 memory speeds (up to 667MHz). ATI will also debut its next-generation AMD- and Intel-oriented chipsets (code-named RS482 and RC410) in June. If anything else is moving in this market, it’s wireless networking chipsets. According to IC Insights, the market is expected to show an average annual growth rate of 23% in dollars and 35% in unit shipments from 2004 to 2008. Specifically, the 802.11 chipset portion of the wireless networking market is forecasted to grow from $680 million in 2004 to $1.5 billion in 2008, representing an average annual growth rate of 21%. Watch for the average selling price in this market to fall from $17 in 2004 to $12 in 2008.

IC Insights says the Bluetooth corner of the wireless networking chipset market is expected to expand from $580 million to $1.5 billion over the same four-year period. The average selling price of a Bluetooth chipset in 2008 will be about one-quarter the price of chipsets sold in 2002. And if prices are gauged by what the giants are doing, pay attention to Intel over the next few months. The company will cut the prices of its Grantsdale and Alderwood chipsets by at least $3 by July. Intel has also debuted its next-generation Pentium chipsets, the 945P, 945G, and 955X, which will also see price cuts by July.

Memory
Michael T. Ching, product marketing manager at Rambus, reminds us that DDR2 memory is the hottest technology on the memory scene. Ching says, “Memory bandwidth demands continue to increase across all application segments. In the PC space, multicore CPUs are driving the need for faster memory and will push mainstream DDR2 memory frequencies to 667MHz and beyond.” Ching says Rambus recently demonstrated the industry's fastest drop-in DDR2 memory controller interface, operating at a data rate of 800MHz. Rambus also announced the company’s architectural breakthrough of applying microthreading to DRAM cores.

According to Heather Skinner, corporate public relations manager at Kingston Technology, in the memory market, PC3200 is still the standard, but moving to DDR2 is getting more popular. Skinner shared some DDR2 market scoop from a recent Kingston report. “DDR2 is continually gaining ground as more motherboards are supporting it and prices are dropping. Demand on DDR2 has picked up tremendously.” As for upcoming product announcements, Skinner said, “Outside of DDR2 development and the development of Fully Buffered DIMMs (in 2006 to 2007), we are unable to disclose specific product launches.” According to the experts, these markets remain stable. But the next generation is coming (let’s say 2006 and beyond), when prices will be more attractive and performance will be far better.

Original article by Chris A. MacKinnon

Measure Your Power Usage

2008-08-26T03:17:00.000-07:00

How Do You Get An Accurate Assessment?

Although data center experts urge IT managers to maintain constant control over power and cooling, which are interrelated because one depends on the other, it can be tricky to accurately measure power consumption in a data center.

Any one-time measurement is just a snapshot of a data center’s energy use, notes Greg Smith, business development manager of Electrical Reliability Services for Emerson Network Power’s Liebert Services (www.liebert.com). “Actual energy consumption fluctuates depending on the tasks being performed at [any] given time throughout the day and depends largely on human activity,” he says.

Instead of trying to measure on a daily basis, it may be more productive to measure facility power and data center power periodically, notes Wally Phelps, data center product manager at DegreeC (www.degreec.com). During that measurement period, an SME should take readings several times during the day for several consecutive weeks, he says, which should give a data center manager an idea of consumption. But adding measurement time to the schedule, it turns out, is the easy part.

Meter Use

In general, to get consumption data that’s useful, IT will have to go down to the equipment or device level, says Steve Yellen, vice president of product and market strategy at Aperture (www.aperture.com). "There can be a big difference between the manufacturer's rating of a particular device and the actual power it will consume," he notes. "In the past, data centers have relied on the manufacturer's ratings, but as data centers try to squeeze out more processing capacity from their limited physical resources, they’re increasingly looking to use actual measurement.”

There’s no shortcut or rule of thumb, Yellen says, just a strategy of monitoring devices to see how much they’re consuming and track it over time to identify trends.

To do the work, it’s time for meters. The main meters the power company uses might do a fine job of measuring overall electricity consumption for a building, but data center managers will need submeters. Companies can sometimes borrow submeters from the local electric company, but most often the company must purchase them, Phelps adds.

To make the measurement with the least effort, identify the data center and cooling infrastructure circuits as close to the main feed as possible, Phelps says. In the ideal case, an SME would only need one measurement point, but in many cases, data center circuits will be on different branches or feeds, and the SME will have to use them separately.

Phelps notes that a company can use a single meter and move it to different circuits, but this will be less accurate, especially in climates that change often.

Also important is that power that the cooling infrastructure consumes must be measured exclusive of other building systems. Many data centers have subsystems, and Phelps notes that SMEs should take care in identifying and measuring consumptions of all subsystems. For example, a chilled water system will require measurement of condenser pumps, cooling loop pumps, the chilled water distribution pump, chillers, and cooling tower fans.

Usage & Efficiency

To understand what the numbers mean, Yellen suggests comparing a data center’s energy usage to others within the industry. This information should be easier to obtain soon, he says, because the EPA is forming a comprehensive database of metrics.

In the meantime, companies may want to look at finding ways to calculate efficiency, which Yellen says is very tricky to measure, especially in complex and changeable environments such as data centers. There are two components to calculating efficiency, he notes. First, determine how efficiently the data center is bringing power to IT equipment such as power distribution and cooling by comparing numbers with manufacturer specs and others in the industry.

“If it isn’t efficient, then a right-sizing exercise may be required to ensure that your infrastructure and design and sizing are as efficient as possible,” Yellen says. He adds that a company should make sure that only devices being used are drawing energy because “ghost servers” could have been decommissioned but may still be plugged in.

Secondly, an SME should examine the efficiency of converting energy into information processing. This is the trickier part of the equation, Yellen believes, because it goes to the level of how efficiently the enterprise is using computing resources. He says, “This is the area where server utilization and virtualization and the efficiency of the software in using the processor come into play.”

Potential Pitfalls

One challenge that could crop up during the measurement is a lack of funding for extensive submetering, particularly if there are numerous pieces of equipment that require the strategy. DegreeC’s Phelps notes that some meters can cost about $1,000 each, so having to assess several locations can be costly.

For those situations, Smith believes a thorough electrical assessment performed as part of an overall data center assessment is the most cost-effective way to get a basic understanding of energy consumption, even if it doesn’t go into the type of deeper detail submetering provides. “This type of assessment will include measurement of the load per UPS unit,” Smith says. “These measurements of IT energy consumption, when repeated at various peak and nonpeak times and considered in conjunction with overall facility power use, can provide some context for understanding actual data center energy consumption.”

Another challenge may be hybrid systems. Although most data centers consume only electricity, some do use other forms of energy, such as natural gas, diesel, and even steam, says Phelps. Because an SME must measure all energy for an accurate reading, submeters can capture data and an IT manager should convert the energy units to BTUs.

For example, diesel is measured in gallons, while natural gas is measured in therms, so both would have to be converted to BTUs, much as kilowatts will have to be, to use a standard measure.

Finally, seasonal variation can play a large part in cooling demands and efficiency. In general, Phelps notes, data centers will be more efficient in winter months than in summer, and SMEs should consider that spike in demand when making any decisions on tweaking procedures and equipment after the consumption data is collected.

Original Article by Elizabeth Millard
www.processor.com

NX Bit

2008-08-26T03:08:00.000-07:00

( From Wikipedia, the free encyclopedia )

The NX bit, which stands for No eXecute, is a technology used in CPUs to segregate areas of memory for use by either storage of processor instructions (or code) or for storage of data, a feature normally only found in Harvard architecture processors. However, the NX bit is being increasingly used in conventional von Neumann architecture processors, for security reasons.

Any section of memory designated with the NX attribute means that it may only be used for storing data, so that processor instructions should not reside there, and cannot be executed if they do. The general technique, known as executable space protection, is used to prevent certain types of malicious software from taking over computers by inserting their code into another program's data storage area and running their own code from within this section; this is known as a buffer overflow attack.

Intel has decided to market the feature as the XD bit, for eXecute Disable. However, Intel's XD bit and AMD's NX bit perform the same function and are different only in name.

Hardware background

x86 processors, since the 80286, included a similar capability implemented at the segment level. However, such control mechanism is too coarse to be useful, especially for modern software that uses flat memory model. A new mechanism was needed to control execution per page rather than per whole segment.

The page-level mechanism has been around for years in various other processor architectures such as Sun's SPARC, Alpha, and IBM's PowerPC. Intel implemented a similar feature in its Itanium (Merced) processor—having IA-64 architecture—in 2001, but did not bring it to the more popular x86 processor families (Pentium, Celeron, Xeon, etc). In x86 architecture it was implemented by AMD, as NX bit, for use by its AMD64 line of processors, such as the Athlon 64 and Opteron. The term NX bit seems to have now become commonly used to generically describe similar technologies in other processors.

After AMD's decision to include this functionality in its AMD64 instruction set, Intel implemented a similar feature in x86 processors beginning with the Pentium 4 processors based on later iterations of the Prescott core.

The NX bit specifically refers to bit number 63 (i.e. the most significant bit) of a 64-bit entry in the page table. If this bit is set to 0, then code can be executed from that page; if set to 1, code cannot be executed from that page, and anything residing there is assumed to be data. Also note that it is used only with Physical Address Extension (PAE) page table format, because the x86's original 32-bit page table format obviously has no bit 63.

A similar functionality was introduced in the Burroughs 5000 in 1961, and retained in its successors at least through 2006. In its implementation of tagged architecture, each word of memory had an associated, hidden tag bit designating it code or data. Thus, user programs cannot write or even read a program word, and data words cannot be executed.

Software emulation of feature

Prior to the onset of this feature within the hardware, various operating systems attempted to emulate this feature through software, such as W^X or Exec Shield. They are described later in this article.

An operating system with the ability to emulate and/or take advantage of an NX bit may prevent the stack and heap memory areas from being executable, and may prevent executable memory from being writable. This helps to prevent certain buffer overflow exploits from succeeding, particularly those that inject and execute code, such as the Sasser and Blaster worms. These attacks rely on some part of memory, usually the stack, to be both writable and executable; if it is not, the attack fails.

Implementations

Many operating systems implement or have an available NX policy, and some implement or have available NX emulation. Here is a list of such systems in alphabetical order, each with technologies ordered from newest to oldest.

For some technologies, there is a summary which gives the major features each technology supports. The summary is structured as below.

Hardware Supported Processors: (Comma separated list of CPU architectures)
Emulation: (No) or (Architecture Independent) or (Comma separated list of CPU architectures)
Other Supported: (None) or (Comma separated list of CPU architectures)
Standard Distribution: (No) or (Yes) or (Comma separated list of distributions or versions which support the technology)
Release Date: (Date of first release)

A technology supplying Architecture Independent emulation will be functional on all processors which aren't hardware supported. The "Other Supported" line is for processors which allow some grey-area method, where an explicit NX bit doesn't exist yet hardware allows one to be emulated in some way.

FreeBSD

Initial PG_NX support first appeared in FreeBSD -CURRENT on June 8, 2004 and is a part of FreeBSD since 5.3 release.

Linux

Linux kernel currently supports standard hardware NX on CPUs that support it, such as the current 64-bit CPUs of AMD, Intel, Transmeta and VIA.

The support for this feature in the 64-bit mode on x86_64 CPUs was added in 2004 by Andi Kleen, and later the same year, Ingo Molnar added support for the NX bit in 32-bit mode on 64-bit CPUs. These features have been in the stable Linux kernel since release 2.6.8 in August 2004.

The availability of the NX bit on 32-bit x86 kernels, which may run on both 32-bit x86 CPUs and 64-bit x86 compatible CPUs, is significant because a 32-bit x86 kernel would not normally expect the NX bit that an AMD64 or IA-64 supplies; the NX enabler patch assures that these kernels will attempt to use the NX bit if present.

Some desktop Linux distributions such as Fedora Core 6, Ubuntu and openSUSE do not enable the HIGHMEM64 option, which is required to gain access to the NX bit in 32-bit mode, in their default kernel; this is because the PAE mode that is required to use the NX bit causes pre-Pentium Pro (including Pentium MMX) and Celeron M and Pentium M processors without NX support to fail to boot. Other processors that do not support PAE are AMD K6 and earlier, Transmeta Crusoe, VIA C3 and earlier, and Geode GX and LX. Older versions of VMware, and even current versions of Microsoft Virtual PC and Parallels does not support PAE on the guest. Fedora Core 6 does provide a kernel-PAE package which supports PAE and NX though.

Non-execute functionality has also been present for other non-x86 processors supporting this functionality for many releases.

Exec Shield

Red Hat kernel developer Ingo Molnar released a Linux kernel patch named Exec Shield to approximate and use NX functionality on 32-bit x86 CPUs.

The Exec Shield patch was released to the Linux kernel mailing list on May 2, 2003. It was rejected for merging with the base kernel because it involved some intrusive changes to core code in order to handle the complex parts of the emulation trick.

Hardware Supported Processors: All that Linux supports NX on
Emulation: NX approximation using the code segment limit on IA-32 (x86) and compatible
Other Supported: None
Standard Distribution: Fedora Core and Red Hat Enterprise Linux
Release Date: May 2, 2003

PaX

The PaX NX technology can emulate an NX bit or NX functionality, or use a hardware NX bit. PaX works on x86 CPUs that do not have the NX bit, such as 32-bit x86.

The PaX project originated October 1, 2000. It was later ported to 2.6, and is at the time of this writing still in active development.

The Linux kernel still does not ship with PaX (as of March, 2008); the patch must be merged manually.

Hardware Supported Processors: Alpha, AMD64, IA-64, MIPS (32 and 64 bit), PA-RISC, PowerPC, SPARC
Emulation: IA-32 (x86)
Other Supported: PowerPC (32 and 64 bit), SPARC (32 and 64 bit)
Standard Distribution: Adamantix, Hardened Gentoo, Hardened Linux
Release Date: October 1, 2000

Mac OS X

Mac OS X for Intel supports the NX bit on all CPUs supported by Apple (from 10.4.4 – the first Intel release – onwards).

Microsoft Windows

Starting with Windows XP Service Pack 2 and Windows Server 2003 Service Pack 1, the NX features were implemented for the first time on the x86 architecture.

Microsoft Windows uses NX protection on critical Windows services exclusively by default. Under Windows XP or Server 2003, the feature is called Data Execution Prevention (abbreviated DEP), and it can be configured through the advanced properties of the "My Computer" icon. If the x86 processor supports this feature in hardware, then the NX features are turned on automatically in Windows XP/Server 2003 by default. If the feature is not supported by the x86 processor, then no protection is given.

"Software DEP" is unrelated to the NX bit, and is what Microsoft calls their enforcement of Safe Structured Exception Handling. Software DEP/SafeSEH checks when an exception is thrown to make sure that the exception is registered in a function table for the application, and requires the program to be built with it. This is likely a countermeasure to handle an exploit possible because of the way DEP handles NX faults; while most other technologies simply terminate the program unquestioningly, DEP raises an exception. It is not possible for a program to truly recover from an attack because program flow is destroyed in an unrecoverable manner.

Early implementations of DEP provided no address space layout randomization (ASLR), which allowed potential return-to-libc attacks that could have been feasibly used to disable DEP during an attack. The PaX documentation elaborates on why ASLR is necessary; a proof-of-concept was produced detailing a method by which DEP could be circumvented in the absence of ASLR. It may be possible to develop a successful attack if the address of prepared data such as corrupted images or MP3s can be known by the attacker. Microsoft added ASLR functionality in Windows Vista and Windows Server 2008 to address this avenue of attack.

Outside of the x86 sphere, a version of NX also exists for Intel's IA-64 which is implemented in Windows on that architecture.

Hardware Supported Processors: x86-64 (AMD64 and Intel 64), IA-64, Efficeon, Pentium M (later revisions), AMD Sempron (later revisions)
Emulation: No
Other Supported: None
Standard Distribution: Windows XP Service Pack 2, Windows Server 2003 Service Pack 1, Windows XP Professional x64 Edition, Windows Vista
Release Date: August 6, 2004

NetBSD

As of NetBSD 2.0 and later (December 9, 2004), architectures which support it have non-executable stack and heap.

Those which have per-page granularity consist of: amd64, sparc64, sparc (sun4m, sun4d), powerpc (ibm4xx), alpha, sh5, hppa.

Those which can only support these with region granularity are: powerpc (eg. macppc), i386.

Other architectures do not benefit from non-executable stack or heap, NetBSD not by default using any software emulation to offer these features.

[edit] OpenBSD

W^X

A technology in the OpenBSD operating system, known as W^X, currently takes advantage of the NX bit in the AMD64 port. OpenBSD also supports W^X on some CPUs without an NX bit.

W^X makes use of the NX bit on Alpha, AMD64, HPPA, and SPARC processors. Intel 64 processors may or may not be supported, depending on hardware[1]. Intel added the NX (called XD by Intel) support to its later chips.

OpenBSD 3.3 shipped May 1, 2003, and was the first operating system to include W^X.

Hardware Supported Processors: Alpha, AMD64, HPPA, SPARC
Emulation: IA-32 (x86)
Other Supported: None
Standard Distribution: Yes
Release Date: May 1, 2003

Solaris

Solaris has supported globally disabling stack execution on SPARC processors since Solaris 2.6 (1997); in Solaris 9 (2002), support for disabling stack execution on a per-executable basis was added.

As of Solaris 10 (2005), NX protection is automatically enabled by default on x86 processors that support this feature. Exceptions are made for the 32-bit legacy ABI's treatment of a program's stack segment. The vast majority of programs will work without changes. However, if a program fails, the protection may be disabled via the enforce-prot-exec EEPROM option. Sun recommends that failures should be reported as program bugs.^{[citation needed]}

Functional comparison of technologies

Here, features of the NX technologies will be compared and contrasted.

Generally, NX bit emulation is available only on x86 CPUs. The sections within dealing with emulation are concerned only with x86 CPUs unless otherwise stated.

While it has been proven that some NX bit emulation methods incur an extremely low overhead, it has also been proven that such methods can become inaccurate. On the other hand, other methods may incur an extremely high overhead and be absolutely accurate. No method has been discovered as of yet without a significant trade-off, whether in processing power, accuracy, or virtual memory space.

Overhead

Overhead is the amount of extra CPU processing power that is required for each technology to function. It is important because technologies which somehow emulate or supply an NX bit will usually impose a measurable overhead; while using a hardware supplied NX bit will impose no measurable overhead. All technologies create overhead due to the extra programming logic that must be created to control the state of the NX bit for various areas of memory; however, evaluation usually handled by the CPU itself when a hardware NX bit exists, and thus produces no overhead.

On CPUs supplying a hardware NX bit, none of the listed technologies imposes any significant measurable overhead unless explicitly noted.

Exec Shield

Exec Shield's legacy CPU support approximates (Ingo Molnar's word for it) NX emulation by tracking the upper code segment limit. This imposes only a few cycles of overhead during context switches, which is for all intents and purposes immeasurable.

PaX

PaX supplies two methods of NX bit emulation, called SEGMEXEC and PAGEEXEC.

The SEGMEXEC method imposes a measurable but low overhead, typically less than 1%. This is a constant scalar incurred due to the virtual memory mirroring used. SEGMEXEC also has the effect of halving the task's virtual address space, allowing the task to access less memory than it normally could. This is not a problem until the task requires access to more than half the normal address space, which is rare. SEGMEXEC does not cause programs to use more system memory (i.e. RAM); it only restricts how much they can access. On 32-bit CPUs, this becomes 1.5 GiB rather than 3 GiB.

PaX supplies a method similar to Exec Shield's approximation in the PAGEEXEC as a speedup; however, when higher memory is marked executable, this method loses its protections. In these cases, PaX falls back to the older, variable overhead method used by PAGEEXEC to protect pages below the CS limit, which may become a quite high overhead operation in certain memory access patterns.

When the PAGEEXEC method is used on a CPU supplying a hardware NX bit, the hardware NX bit is used; no emulation is used, thus no significant overhead is incurred.

Accuracy

Some technologies approximately emulate (or approximate) an NX bit on CPUs which do not support them. Others strictly emulate an NX bit for these CPUs, but decrease performance or virtual memory space significantly. Here, these methods will be compared for accuracy.

All technologies listed here are 100% accurate in the presence of a hardware NX bit, unless otherwise stated.

Exec Shield

For legacy CPUs without an NX bit, Exec Shield fails to protect pages below the code segment limit; an mprotect() call to mark higher memory, such as the stack, executable will mark all memory below that limit executable as well. Thus, in these situations, Exec Shield's schemes fails. This is the cost of Exec Shield's low overhead (see above).

PaX

SEGMEXEC does not rely on such volatile systems as that used in Exec Shield, and thus does not encounter conditions in which finegrained NX bit emulation cannot be enforced; it does, however, have the halving of virtual address space mentioned above.

PAGEEXEC will fall back to the original PAGEEXEC method used before the speed-up when data pages exist below the upper code segment limit. In both cases, PaX' emulation remains 100% accurate; no pages will become executable unless the operating system explicitly makes them as such.

It is also interesting to note that PaX supplies mprotect() restrictions to prevent programs from marking memory in ways which produce memory useful for a potential exploit. This policy causes certain applications to cease to function; but can be disabled for affected programs.

Control over restrictions

Some technologies allow executable programs to be marked so that the operating system knows to relax the restrictions imposed by the NX technology for that particular program. Various systems provide various controls; such controls are described here.

Exec Shield

Exec Shield supplies executable markings. Exec Shield only checks for two ELF header markings, which dictate whether the stack or heap needs to be executable. These are called PT_GNU_STACK and PT_GNU_HEAP, respectively. Exec Shield allows these controls to be set for both binary executables and for libraries; if an executable loads a library requiring a given restriction relaxed, the executable will inherit that marking and have that restriction relaxed.

PaX

PaX supplies fine-grained control over protections. It allows individual control over the following functions of the technology for each binary executable:

Executable space protections
- PAGEEXEC
- SEGMEXEC
mprotect() restrictions
Trampoline emulation
Randomized executable base
Randomized mmap() base

See the PaX article for more details about these restrictions.

PaX completely ignores both PT_GNU_STACK and PT_GNU_HEAP. There was a point in time when PaX had a configuration option to honor these settings; that option has henceforth been intentionally removed for security reasons, as it was deemed not useful. The same results of PT_GNU_STACK can normally be attained by disabling mprotect() restrictions, as the program will normally mprotect() the stack on load. This may not always be true; for situations where this fails, simply disabling both PAGEEXEC and SEGMEXEC will effectively remove all executable space restrictions, giving the task the same protections on its executable space as a non-PaX system.

Windows

When NX is supported, it is enabled by default. Windows allows programs to control which pages disallow execution through its API as well as through the section headers in a PE file.

In the API, runtime access to the NX bit is exposed through the Win32 API calls VirtualAlloc[Ex] and VirtualProtect[Ex]. In these functions, a page protection setting is specified by the programmer. Each page may be individually flagged as executable or non-executable. Despite the lack of previous x86 hardware support, both executable and non-executable page settings have been provided since the beginning. On pre-NX CPUs, the presence of the 'executable' attribute has no effect. It was documented as if it did function, and, as a result, most programmers used it properly.

In the PE file format, each section can specify its executability. The execution flag has existed since the beginning of the format; standard linkers have always used this flag correctly, even long before the NX bit.

Because of these things, Windows is able to enforce the NX bit on old programs. Assuming the programmer complied with "best practices", applications should work correctly now that NX is actually enforced. Only in a few cases have there been problems; Microsoft's own .NET Runtime had problems with the NX bit and was updated.

Xbox

In Microsoft's Xbox, although the CPU does not have the NX bit, newer versions of the XDK set the code segment limit to the beginning of the kernel's .data section (no code should be after this point in normal circumstances). This was probably in response to the 007: Agent Under Fire saved game exploit^{[citation needed]}; however, this change does not fix the problem, as the memory from which the payload executes is well below the beginning of the kernel's .data section.

Starting with version 51xx, this change was also implemented into the kernel of new Xboxes. This broke the techniques old exploits used to become a TSR; new versions were quickly released supporting this new version because the fundamental exploit was unaffected.

Computer Hardware

2008-08-26T02:55:00.000-07:00

( From Wikipedia the free encyclopedia )

Computer hardware is the physical part of a computer, including its digital circuitry, as distinguished from the computer software that executes within the hardware. The hardware of a computer is infrequently changed, in comparison with software and hardware data, which are "soft" in the sense that they are readily created, modified or erased on the computer. Firmware is a special type of software that rarely, if ever, needs to be changed and so is stored on hardware devices such as read-only memory (ROM) where it is not readily changed (and is, therefore, "firm" rather than just "soft").

Most computer hardware is not seen by normal users. It is in embedded systems in automobiles, microwave ovens, electrocardiograph machines, compact disc players, and other devices. Personal computers, the computer hardware familiar to most people, form only a small minority of computers (about 0.2% of all new computers produced in 2003). See Market statistics.

Typical PC hardware

A typical personal computer consists of a case or chassis in a tower shape (desktop) and the following parts:

Internals of typical personal computer.

Inside a Custom Computer.

Motherboard

* Motherboard - It is the "body" or mainframe of the computer, through which all other components interface.

Central processing unit (CPU) - Performs most of the calculations which enable a computer to function, sometimes referred to as the "brain" of the computer.
- Computer fan - Used to lower the temperature of the computer; a fan is almost always attached to the CPU, and the computer case will generally have several fans to maintain a constant airflow. Liquid cooling can also be used to cool a computer, though it focuses more on individual parts rather than the overall temperature inside the chassis.

'* Random Access Memory (RAM)' -It is also known as the physical memory of computer. Fast-access memory that is cleared when the computer is powered-down. RAM attaches directly to the motherboard, and is used to store programs that are currently running. * Firmware is loaded from the Read only memory ROM run from the Basic Input-Output System (BIOS) or in newer systems Extensible Firmware Interface (EFI) compliant

Internal Buses - Connections to various internal components.
- PCI
- PCI-E
- USB
- HyperTransport
- CSI (expected in 2008)
- AGP (being phased out)
- VLB (outdated)
External Bus Controllers - used to connect to external peripherals, such as printers and input devices. These ports may also be based upon expansion cards, attached to the internal buses.
- parallel port
- serial port
- USB
- Firewire
- SCSI (On Servers and older machines)
- PS/2 (For mice and keyboards, being phased out and replaced by USB.)
- ISA (outdated)
- EISA (outdated)
- MCA (outdated)

Power supply

Main article: Computer power supply

A case control, and (usually) a cooling fan, and supplies power to run the rest of the computer, the most common types of power supplies are AT and BabyAT (old) but the standard for PCs actually are ATX and Micro ATX.

Storage controllers

Controllers for hard disk, CD-ROM and other drives like internal Zip and Jaz conventionally for a PC are IDE/ATA; the controllers sit directly on the motherboard (on-board) or on expansion cards, such as a Disk array controller. IDE is usually integrated, unlike SCSISmall Computer System Interface which is found in most servers. The floppy drive interface is a legacy MFM interface which is now slowly disappearing. All these interfaces are gradually being phased out to be replaced by SATA and SAS.

Video display controller

Main article: Graphics card

Produces the output for the visual display unit. This will either be built into the motherboard or attached in its own separate slot (PCI, PCI-E, PCI-E 2.0, or AGP), in the form of a Graphics Card.

Removable media devices

Main article: Computer storage

CD (compact disc) - the most common type of removable media, inexpensive but has a short life-span.
- CD-ROM Drive - a device used for reading data from a CD.
- CD Writer - a device used for both reading and writing data to and from a CD.
DVD (digital versatile disc) - a popular type of removable media that is the same dimensions as a CD but stores up to 6 times as much information. It is the most common way of transferring digital video.
- DVD-ROM Drive - a device used for reading data from a DVD.
- DVD Writer - a device used for both reading and writing data to and from a DVD.
- DVD-RAM Drive - a device used for rapid writing and reading of data from a special type of DVD.
Blu-ray - a high-density optical disc format for the storage of digital information, including high-definition video.
- BD-ROM Drive - a device used for reading data from a Blu-ray disc.
- BD Writer - a device used for both reading and writing data to and from a Blu-ray disc.
HD DVD - a high-density optical disc format and successor to the standard DVD. It was a discontinued competitor to the Blu-ray format.
Floppy disk - an outdated storage device consisting of a thin disk of a flexible magnetic storage medium.
Zip drive - an outdated medium-capacity removable disk storage system, first introduced by Iomega in 1994.
USB flash drive - a flash memory data storage device integrated with a USB interface, typically small, lightweight, removable, and rewritable.
Tape drive - a device that reads and writes data on a magnetic tape, usually used for long term storage.

Internal storage

Hardware that keeps data inside the computer for later use and remains persistent even when the computer has no power.

Hard disk - for medium-term storage of data.
Solid-state drive - a device similar to hard disk, but containing no moving parts.
Disk array controller - a device to manage several hard disks, to achieve performance or reliability improvement.

Sound card

Main article: Sound card

Enables the computer to output sound to audio devices, as well as accept input from a microphone. Most modern computers have sound cards built-in to the motherboard, though it is common for a user to install a separate sound card as an upgrade.

Networking

Main article: Computer networks

Connects the computer to the Internet and/or other computers.

Modem - for dial-up connections
Network card - for DSL/Cable internet, and/or connecting to other computers.
Direct Cable Connection - Use of a null modem, connecting two computers together using their serial ports or a Laplink Cable, connecting two computers together with their parallel ports.

dial up connections broad band connections

Other peripherals

Main article: Peripheral

In addition, hardware devices can include external components of a computer system. The following are either standard or very common.

Wheel mouse

Includes various input and output devices, usually external to the computer system

Input

Main article: Input

Text input devices
- Keyboard - a device, to input text and characters by depressing buttons (referred to as keys), similar to a typewriter. The most common English-language key layout is the QWERTY layout.
Pointing devices
- Mouse - a pointing device that detects two dimensional motion relative to its supporting surface.
- Trackball - a pointing device consisting of an exposed portruding ball housed in a socket that detects rotation about two axes.
- Xbox 360 Controller - A controller used for Xbox 360, Which with the use of the application Switchblade(tm), can be used as an additional pointing device with the left or right thumbstick.
Gaming devices
- Joystick - a general control device that consists of a handheld stick that pivots around one end, to detect angles in two or three dimensions.
- Gamepad - a general game controller held in the hand that relies on the digits (especially thumbs) to provide input.
- Game controller - a specific type of controller specialized for certain gaming purposes.
Image, Video input devices
- Image scanner - a device that provides input by analyzing images, printed text, handwriting, or an object.
- Webcam - a low resolution video camera used to provide visual input that can be easily transferred over the internet.
Audio input devices
- Microphone - an acoustic sensor that provides input by converting sound into an electrical signals

Computer Cooling

2008-08-26T02:43:00.000-07:00

Computer cooling is the process of removing heat from computer components.

An OEM AMD heatsink mounted on to a motherboard.

A computer system's components produce large amounts of heat during operation, including integrated circuits such as CPUs, chipset and graphics cards, along with hard drives. This heat must be dissipated in order to keep these components within their safe operating temperatures, and both manufacturing methods and additional parts are used to keep the heat at a safe level. This is done mainly using heat sinks to increase the surface area which dissipates heat, fans to speed up the exchange of air heated by the computer parts for cooler ambient air, and in some cases softcooling, the throttling of computer parts in order to decrease heat generation.

Overheated parts generally exhibit a shorter maximum life-span and may give sporadic problems resulting in system freezes or crashes.

Causes of heat build up

The amount of heat generated by an integrated circuit (e.g., a CPU or GPU), the prime cause of heat build up in modern computers, is a function of the efficiency of its design, the technology used in its construction and the frequency and voltage at which it operates.

The dust on the laptop CPU heat sink after three years of use has made the laptop unusable due to frequent thermal shutdowns.

In operation, the temperature levels of a computer's components will rise until the temperature gradient between the computer parts and their surroundings is such that the rate at which heat is lost to the surroundings is equal to the rate at which heat is being produced by the electronic component, and thus the temperature of the component reaches equilibrium.

For reliable operation, the equilibrium temperature must be sufficiently low for the structure of the computer's circuits to survive.

Additionally, the normal operation of cooling methods can be hindered by other causes, such as:

Dust acting as a thermal insulator and impeding airflow, thereby reducing heat sink and fan performance.
Poor airflow (including turbulence) due to friction that reduces the amount of air flowing through a case, possibly causing stable whirlpools of hot air in certain areas.^{[citation needed]}
Poor heat transfer due to a lack or poor application of thermal compounds.

Damage prevention

It is common practice to include thermal sensors in the design of certain computer parts, e.g. CPUs and GPUs, along with internal logic that shuts down the computer if reasonable bounds are exceeded. It is however unwise to rely on such preventative measures, as it is not universally implemented, and may not prevent repeated incidents from permanently damaging the integrated circuit.

The design of an integrated circuit may also incorporate features to shut down parts of the circuit when it is idling, or to scale back the clock speed under low workloads or high temperatures, with the goal of reducing both power use and heat generation.

System cooling

Fan from Papst for racks.

Air cooling

Further information: Computer fan

While any method used to move air around or to computer enclosures would count as air cooling, fans are by far the most commonly used implement for accomplishing that task. The term computer fan usually refers to fans attached to computer enclosures, but may also be intended to signify any other computer fan, such as a CPU fan, GPU fan, a chipset fan, PSU fan, HDD fan, or PCI slot fans. Common fan sizes include 40, 60, 80, 90, and 120 mm.

In desktops

Airflow through a desktop ATX case.

Desktop computers typically use one or more fans for heat management. Almost all desktop power supplies have at least one fan to exhaust air from the case. Most manufacturers recommend bringing cool, fresh air in at the bottom front of the case, and exhausting warm air from the top rear.

If there is more air being forced into the system than being pumped out (due to an imbalance in the number of fans), this is referred to as a "positive" airflow, as the pressure inside the unit would be higher than outside. A balanced or neutral airflow is the most efficient^{[citation needed]}, although a slightly positive airflow results in less dust build up if dust filters are used.

With recent researches and studies, some companies are making noiseless computers.

In high density computing

Data centers typically contain many racks of flat 1U servers. Air is drawn in at the front of the rack and exhausted at the rear. Because data centers typically contain such large numbers of computers and other power-consuming devices, they risk overheating of the various components if no additional measures are taken. Thus, extensive HVAC systems are used. Often a raised floor is used so the area under the floor may be used as a large plenum for cooled air and power cabling.

In laptop computing

Laptops are typically made to rest on a solid surface. Unfortunately a flat surface is the least desirable angle to dissipate heat, lower temperatures are achieved by a chimney effect when a laptop is set at an angle from horizontal^{[citation needed]}. It is important to note that laptops are neither designed for nor should they be used on surfaces or in spaces which impede the free flow of air (such as carpet or bed linens), as heat damage and/or thermal shutdown/slow-down may occur.

Laptop stands are accessories which, besides raising the laptops screen to another height, are also meant to reduce airflow restrictions.

Liquid submersion cooling

An uncommon practice is to submerse the computer's components in a thermally conductive liquid. Personal computers that are cooled in this manner do not generally require any fans or pumps, and may be cooled exclusively by passive heat exchange between the computer's parts, the cooling fluid and the ambient air. Extreme density computers such as the Cray-2 may use additional radiators in order to facilitate heat exchange.

The liquid used must have sufficiently low electrical conductivity in order for it not to interfere with the normal operation of the computer's components. If the liquid is somewhat electrically conductive, it may be necessary to insulate certain parts of components susceptible to electromagnetic interference, such as the CPU.^[1] For these reasons, it is preferred that the liquid be dielectric.

Liquids commonly used in this manner include various liquids invented and manufactured for this purpose by 3M, such as Fluorinert. Various oils, including but not limited to cooking, motor and silicone oils have all been successfully used for cooling personal computers.

Evaporation can pose a problem, and the liquid may require either to be regularly refilled or sealed inside the computer's enclosure. Liquid may also slowly seep into and damage components, particularly capacitors, causing an initially functional computer to fail after hours or days immersed.

Waste heat reduction

Where full-power, full-featured modern computers are not required, some companies opt to use less powerful computers or computers with fewer features. For example: in an office setting, the IT department may choose a thin client or a diskless workstation thus cutting out the heat-laden components such as hard drives and optical disks. These devices are also often powered with direct current from an external power supply brick which still wastes heat, but not inside the computer itself.

The components used can greatly affect the power consumption and hence waste heat. A VIA EPIA motherboard with CPU typically uses approximately 25 watts of heat whereas a Pentium 4 motherboard typically uses around 140 watts. While the former has considerably less computing power, both types are adequate and responsive for tasks such as word processing and spreadsheets. Choosing a LCD monitor rather than a CRT can also reduce power consumption and excess room heat.

Conductive and radiative cooling

Some laptop components, such as hard drives and optical drives, are commonly cooled by having them make contact with the computer's frame, increasing the surface area which can radiate and otherwise exchange heat.

Spot cooling

In addition to system cooling, various individual components usually have their own cooling systems in place. Components which are individually cooled include, but are not limited to, the CPU, GPU, hard disk, and the Northbridge chip. Some cooling solutions employ one or more methods of cooling, and may also utilize logic and/or temperature sensors in order to vary the power used in active cooling components.

Passive heat sink cooling

Passive heatsink fitted on a Intel GMA graphics chip

This involves attaching a block of machined metal to the part that needs cooling. An adhesive may be used, or more commonly for a personal computer CPU, a clamp is used to affix the heat sink tight over the chip, with a thermally conductive pad or gel spread in-between. This block usually has fins and ridges to increase its surface area. The heat conductivity of metal is much better than that of air, and its ability to radiate heat is better than that of the component part it is protecting (usually an integrated circuit or CPU). Until recently, fan cooled aluminium heat sinks were the norm for desktop computers. Today many heat sinks feature copper base-plates or are entirely made of copper, and mount fans of considerable size and power.

Heat sinks tend to get less effective with time due to the build up of dust between their metal fins, which reduces the efficiency with which the heat sink transfers heat to the ambient air. Dust build up is commonly countered with canned air, which are used to blow away the dust along with any other unwanted excess material.

Passive heat sinks are commonly found on older CPUs, parts that do not get very hot (such as the chipset), and low-power computers.

Active heat sink cooling

This uses the same principle as a passive heat sink cooler, with the only difference being that a fan is directed to blow over or through the heat sink. This results in more air being blown through the heat sink, increasing the rate at which the heat sink can exchange heat with the ambient air. Active heat sinks are the primary method of cooling a modern day processor or graphics card.

The buildup of dust is greatly increased with active heat sink cooling as the fan is continually taking in the dust present in the surrounding air. As a result, dust removal procedures need to be exercised much more frequently than with passive heat sink methods.

Peltier cooling or thermoelectric cooling

Main article: Thermoelectric cooling

In 1821 T. J. Seebeck discovered that different metals, connected at two different junctions, will develop a micro-voltage if the two junctions are held at different temperatures. This effect is known as the "Seebeck effect"; it is the basic theory behind the TEC (thermoelectric cooling).

In 1834 Jean Peltier discovered the inverse of the Seebeck effect, now known as the "Peltier effect". He found that applying a voltage to a thermocouple creates a temperature differential between two sides. This results in an effective, albeit extremely inefficient heat pump.

Modern TECs use several stacked units each composed of dozens or hundreds of thermocouples laid out next to each other, which allows for a substantial amount of heat transfer. A combination of bismuth and telluride is most commonly used for thermocouples.

Since TECs are active heat pumps, they are capable of cooling PC components below ambient temperatures, which is impossible with common radiator cooled water cooling systems and heatpipe HSFs.

Water cooling

Main article: Water cooling

DIY Watercooling setup showing 12v pump, CPU Waterblock and the typical application of a T-Line.

While originally limited to mainframe computers, computer watercooling has become a practice largely associated with overclocking in the form of either manufactured "kits" or in the form of DIY setups assembled from individually gathered parts. Lately watercooling has seen increasing use in pre-assembled desktop computers. Water cooling can extract more heat from the cooled parts, which makes it suitable for overclocking, and opposed to air cooling it is less influenced by the ambient temperature. One of it's disadvanteges is the potential for a coolant leak, which can damage electronic components. An advantage is that a water cooling system is not limited to one component, so it can cool the CPU, GPU and other components at the same time.

Heat pipe

Main article: Heat pipe

A heat pipe is a hollow tube containing a heat transfer liquid. As the liquid evaporates, it carries heat to the cool end, where it condenses and then returns to the hot end (under capillary action). Heat pipes thus have a much higher effective thermal conductivity than solid materials. For use in computers, the heat sink on the CPU is attached to a larger radiator heat sink. Both heat sinks are hollow as is the attachment between them, creating one large heat pipe that transfers heat from the CPU to the radiator, which is then cooled using some conventional method. This method is expensive and usually used when space is tight (as in small form-factor PCs), or absolute quiet is needed (such as in computers used in audio production studios during live recording).

Phase-change cooling

An extremely effective way to cool the processor. A vapor compression phase-change cooler is a unit which usually sits underneath the PC, with a tube leading to the processor. Inside the unit is a compressor, the same type that cools a freezer. The compressor compresses a gas (or mixture of gases) which condenses it into a liquid. Then, the liquid is pumped up to the processor, where it passes through an expansion device, this can be from a simple capillary tube to a more elaborate thermal expansion valve. The liquid evaporates changing phase, thereby absorbing the heat from the processor, as it draws extra energy from its environment to accomdate this change (see latent heat). This evaporation can produce temperatures reaching around −15 to -150 degrees Celsius. The gas flows down to the compressor and the cycle begins over again. This way, the processor can be cooled to temperatures ranging from −15 to −150 degrees Celsius, depending on the load, wattage of the processor, the refrigeration system (see refrigeration) and the gas mixture used. This type of system suffers from a number of issues but mainly one must be concerned with dewpoint and proper insulation of all sub-ambient surfaces must be done otherwise the pipes will sweat dripping water on sensitive electronics.

Alternately a new breed of cooling system is being developed inserting a pump into the thermo siphon loop. This adds another degree of flexibility for the design engineer as the heat can now be effectively transported away from the heat source and either reclaimed or dissipated to ambient. Junction temperature can be tuned by adjusting the system pressure; higher pressure equals higher fluid saturation temperatures. This allows for smaller condensers, smaller fans and/or the effective dissipation of heat in a high ambient environment. These systems are in essence the next generation liquid cooling paradigm as they are approximately 10x more efficient than single phase water. Since the system uses a dielectric as the heat transport media leaks do not cause a catastrophic failure of the electric system.

This type of cooling is seen as a more extreme way to cool components, since the units are relatively expensive compared to the average desktop. They also generate a significant amount of noise, since they are essentially miniature refrigerators, however the compressor choice and air cooling system is the main determinant of this, allowing for flexibility for noise reduction based on the parts chosen.

Liquid nitrogen

Liquid nitrogen may be used to cool an overclocked PC.

As liquid nitrogen evaporates at -196 °C, far below the freezing point of water, it is valuable as a phase-change coolant, bringing the additional advantages of being non-toxic and non-combustible.

In a typical installation of liquid nitrogen cooling, fans blow air onto the heat sink of the CPU, as water is pumped through a pipe which ends over the heat sink, and similarly liquid nitrogen can be pushed out of a dewar through a pipe which ends over the heat sink. The short, yet wide nitrogen exhaust ends in a basing on the floor of the housing. Evaporating nitrogen pushes away water, which would otherwise condense and lead to short circuits or form ice. Overly drastic cooling will freeze out the dopant states and the semiconductors will stop working.

By welding an open pipe onto a heat sink, and insulating the pipe, it is possible to cool the processor either with liquid nitrogen, which has a temperature below −196°C, or dry ice. However, after the nitrogen evaporates, it has to be refilled. In the realm of personal computers, this method of cooling is seldom used in other contexts than overclocking trial-runs and record-setting attempts, as the CPU will usually expire within a relatively short period of time due to temperature stress caused by changes in internal temperature.

Soft cooling

Softcooling is the practice of utilizing software to take advantage of CPU power saving technologies to minimize energy use. This is done using halt instructions to turn off or put in standby state CPU subparts that aren't being used or by underclocking the CPU.

Undervolting

Undervolting is the practice of running the CPU or any other component with voltages below the device specifications. An undervolted component draws less power and thus produces less heat. However, this generally will make a processor unstable as it no longer has the voltage necessary to carry out instructions error free. As such, in most cases undervolting is accommodated by an underclocking of the processor itself. Keeping the speed/voltage ratio allows a system to be undervolted while maintaining stability. This technique is generally employed by those seeking low-noise systems, as less cooling is needed because of the reduction of heat production.

Cooling and overclocking

Extra cooling is usually required by those who run parts of their computer (such as the CPU and GPU) at higher voltages and frequencies than manufacturer specifications call for, called overclocking. Increasing performance by this modification of settings results in a greater amount of heat generated and thus increasing the risk of damage to components and/or premature failure.

The installation of higher performance, non-stock cooling may also be considered modding. Many overclockers simply buy more efficient, and often, more expensive fan and heat sink combinations, while others resort to more exotic ways of computer cooling, such as liquid cooling, Peltier effect heatpumps, heat pipe or phase change cooling.

There are also some related practices that have a positive impact in reducing system temperatures:

Heat sink lapping

Heat sink lapping is the smoothing and polishing of the contact (bottom) part of a heat sink to increase its heat transfer efficiency. The desired result is a contact area which has a more even surface, as a less even contact surface creates a larger amount of insulating air between the heat sink and the computer part it is attached to. Polishing the surface using a combination of fine sandpaper and abrasive polishing liquids can produce a mirror-like shine, an indicator of a very smooth metal surface. However, it should be noted that even a curved surface can become extremely reflective, yet not particularly flat, as is the case with curved mirrors; thus heat sink quality is based on overall flatness, more than optical properties. Lapping a high quality heat sink can damage it, because, although the heat sink may become shiny, it is likely that more material will be removed from the edges, making the heat sink less effective overall.

If attempted a piece of plate glass should be used as it self-levels as it cools and offers the most economical solution to producing a perfectly flat surface.

Use of exotic thermal conductive compounds

Some overclockers use special thermal compounds whose manufacturers claim to have a much higher efficiency than stock thermal pads. Heat sinks clean of any grease or other thermal transfer compounds have a very thin layer of these products applied, and then are placed normally over the CPU. Many of these compounds have a high proportion of silver as their main ingredient due to its high thermal conductivity. The resulting difference in the temperature of the CPU is measurable (several degrees celsius), but the heat transfer does appear to be much superior to stock compounds. Some people experience negligible gains and have called to question the advantages of these exotic compounds, calling the style of application more important than the compound itself. Also note that there may be a 'setting period' and negligible gains may improve over time as the compound reaches its optimum thermal conductivity.

Use of rounded cables

Most older PCs use flat ribbon cables to connect storage drives (IDE or SCSI). These large flat cables greatly impede airflow by causing drag and turbulence. Overclockers and modders often replace these with rounded cables, with the conductive wires bunched together tightly to reduce surface area. Theoretically, the parallel strands of conductors in a ribbon cable serve to reduce crosstalk (signal carrying conductors inducing signals in nearby conductors), but there is no empirical evidence of rounding cables reducing performance. This may be because the length of the cable is short enough so that the effect of crosstalk is negligible. Problems usually arise when the cable is not electromagnetically protected and the length is considerable, a more frequent occurrence with older network cables.

These computer cables can then be cable tied to the chassis or other cables to further increase airflow.

This is less of a problem with new computers that use Serial ATA which has a much thinner cable.

Airflow optimization

The colder the cooling medium (the air), the more effective the cooling. Cooling air temperature can be reduced by these guidelines:

Supply cool air to the hot components as directly as possible. Examples are air snorkels and tunnels that feed outside air directly and exclusively to the CPU or GPU cooler. For example, the BTX case design prescribes a CPU air tunnel.
Expel warm air as directly as possible. Examples are: Conventional PC (ATX) power supplies blow the warm air out the back of the case. Many dual-slot graphics card designs blow the warm air through the cover of the adjacent slot. There are also some aftermarket coolers that do this. Some CPU cooling designs blow the warm air directly towards the back of the case, where it can be ejected by a case fan.
Air that has already been used to spot-cool a component should not be reused to spot-cool a different component (this follows from the previous items). The ATX case design can be said to violate this rule, since the power supply gets its "cool" air from the inside of the case, where it has been warmed up already. The BTX case design also violates this rule, since it uses the CPU cooler's exhaust to cool the chipset and often the graphics card.
Prefer cool intake air, avoid inhaling exhaust air (outside air above or near the exhausts). For example, a CPU cooling air duct at the back of a tower case would inhale warm air from a graphics card exhaust. Moving all exhausts to one side of the case, conventionally the back, helps to keep the intake air cool.

Fewer fans strategically placed will improve the airflow internally within the PC and thus lower the overall internal case temperature in relation to ambient conditions. The use of larger fans also improves efficiency and lowers the amount of waste heat along with the amount of noise generated by the fans while in operation.

There is little agreement on the effectiveness of different fan placement configurations, and little in the way of systematic testing has been done. For a rectangular PC (ATX) case, a fan in the front with a fan in the rear and one in the top has been found to be a suitable configuration. However, AMD's (somewhat outdated) system cooling guidelines notes that "A front cooling fan does not seem to be essential. In fact, in some extreme situations, testing showed these fans to be recirculating hot air rather than introducing cool air." It may be that fans in the side panels could have a similar detrimental effect -- possibly through disrupting the normal air flow through the case. However, this is unconfirmed and probably varies with the configuration.

References :

From Wikipedia, the free encyclopedia

USB Device - A Little Briefcase

2008-08-25T04:03:00.000-07:00

Did you know USB ?

The process of making a bootable USB is not as easy as it looks to be. This is much tougher than creating a bootable disc or floppy. The USB in many respects is considered to be a better alternative to the floppy drive. In certain aspects these are considered to be better than even the CD or the DVD discs.

The reasons for regarding the Universal Serial Bus Device better than these are many. One major difference is that these are more portable in nature. Moreover, the memory capacity and the protection of the data stored in them can never be compared with that of the other storing devices.

Let us now have a look at the functions and the facilities provided by these drives.

These devices can be connected to the CPU very easily and as soon as the drive is connected, the user is informed about it by a notice or by an indication of the connection of a new drive. In most computers, you have the option of inserting the device into a Universal Serial Bus port either in the back or in the front of the computer. For accessing a file stored in the drive or for sending a file into it, the user just has to copy the file from the device and paste in the computer and vice-versa.

The amount of data that can be stored in the USB device, or Flash drive, is really very huge and that depends on the capacity of the drive. The recent devices that are available in the market are credited with more capacity than the previous ones and therefore, are better than the earlier models. Easy to install and easy to erase, these drives have caught the fancy of users all round the world.

In contrast to the various merits of the device, the demerits are very few or even negligible.

Moreover, the fear of the data getting destroyed or corrupted is almost negligible in USB devices. The CD or DVD discs may get scratched and damaged very easily and therefore important data can never be stored in the discs safely. But it can be safely stored in the USB devices.

The quality of these devices also depends upon the company that has manufactured it. Some of the devices are not as good as those of the top brands. The prices for these may be a bit high, but the effort should always be to go for the costly one. The main reason for this is that the costly pieces will carry a warranty with them. Thus anyone who buys the flash drives of the reputed brands can at least have the freedom of handling and carrying it the way he wants to.

Thus we can see that a small gadget like the USB device has made the task of carrying the files from one place to another much easier than before.

Victor Epand is an expert consultant for computers, laptops and software. When shopping for used computers, used laptops and used software, we recommend you shop at only the best online stores for used computer, used laptop.

Article Source: http://EzineArticles.com/?expert=Victor_Epand

Keep Your Money for Computer

2008-08-25T03:53:00.001-07:00

Original article:
How to Save Time and Money When Buying Computer Hardware and Services for Educational Institutions
By Steve Schlumbaum

From elementary school to universities, computers are becoming the new “teacher’s assistant” and there is no sign of this trend slowing down. Unfortunately, the need for high technology equipment like HP desktops, HP workstations and HP storage devices is growing faster than the budgets needed to support this explosive growth. That’s why it is so important for educational institutions to partner with total technology solution providers who have access to special educational pricing and who have the capabilities and the knowledge needed to help determine computer hardware specifications, prepare quotes and handle the procurement, installation and configuration process.

Navigating the computer hardware purchasing maze can not only be time-consuming, it can be expensive as well. Educational computer hardware pricing varies among suppliers and can even vary within the same supplier depending upon the quantity being purchased and how the HP quote is prepared.

It makes sense that an educational institution placing an order for 50 HP laptops, for example, is going to receive better per-unit pricing than a school that is only ordering one. But that’s not always the case. Many schools are discovering that they can get preferred pricing even if they are only ordering a handful of HP printers IF they place their HP quotes through the right IT service provider.

If your computer hardware requirements include HP desktops, HP notebooks, HP storage devices, HP workstations, or any other HP hardware for educational institutions, here are some time and money-saving tips you can’t afford to ignore:

1. Always partner with HP hardware solutions providers that have experience in the educational institutions channel. These providers can contact HP on your behalf to negotiate the best pricing and delivery times.

2. Only work with an HP hardware solutions provider who will also install and configure your HP computer products and who provide personalized account management. Service that stops after the sale is not really a service at all.

3. Let your educational institution HP computer partner assist you in preparing your HP computer hardware specifications and submitting your HP quotes. This way you’ll have the best chance of specifying the right HP computer products that will provide maximum performance at the lowest possible price.

4. Try to bundle your HP hardware purchases together with other schools in your district, or with your local government or state government agencies, whenever possible. This can help to leverage your buying power even further and can often move your school into the level of “preferred customer” which may result in even better pricing and a higher service-level commitment from your HP solutions provider.

Educational institutions have an obligation to provide their staff and student body with the best available technology and the lowest possible price. Choose the right technology partner and you’ll find that you can buy quality HP laptops, HP servers, HP printers and other HP computer hardware at a fair price and still get all the after-sale support you’ll ever need.

Get personalized assistance with your computer hardware questions and quotes on IT technology products. For more information please visit Steve Schlumbaum's website: http://www.proconfigureit.com

Article Source: http://EzineArticles.com/?expert=Steve_Schlumbaum

How To Select The Right Hardware For Your Home

2008-08-25T03:34:00.000-07:00

If you interest to a computer for your home, be careful! You must very-very select the hardware of your computer. Almost a hardware in market with low quality. A hardware only duplicate from original hardware. So, the quality is lower.

Most people are not aware of how much decorative hardware is used in their home.
If they did, they would see many possibilities to impact their home décor and upgrade the look of their home in a very stylish and easy way.

Take an accounting of your own home.

To get an accurate count make a list of the following decorative hardware in or on your home:
Door handles, door knockers, bell pushes, decorative hinges (not the concealed kind), clavos nails or decorative nails used for show, lever latches, pulls, decorative mortise locks, window hardware, cabinet hardware, gate hardware, garage door hardware, shutter hardware.

Prepare your list in the following way: Down the left side of the sheet list the types of hardware as in the list above. At the top make one column for each of the locations of where the hardware is located (bedroom, bathroom, kitchen, outside front of house, outside back of house, and so forth, in one column note the condition the hardware, in the next to the last column make notes of your sense of how that hardware works with the look of your home and in the last column make notes on a wish list.

Next, check out some hardware sites on the web or go to your nearest decorative hardware store. Note the differences between styles, modern, colonial, old world, Creole, western, a truly wide variety of period styles and the list goes on. So take time to evaluate your choices. Now also note the different finishes available.

Also, you may want to consider the Library of Congress. www.loc.gov. There you can find lots of information on decorative hardware styles and ideas.

Become aware of how much decorative hardware you have in and around your home. And see the many possibilities decorative hardware has to impact your home and upgrade the look of your home in a very stylish and easy way.

Mary Barrett President EHC (European Hardware Company)
800 975-7089 http://www.europeanhardware.net

Article Source: http://EzineArticles.com/?expert=Mary_Barrett

How Hard Discs Work

2008-08-20T22:39:00.000-07:00

Hard discs are the main form of permanent data storage used in computers and, increasingly these days, portable music players, video recorders and even car music players. In a PC, a hard disc is invariably used to store the operating system (e.g. Linux, MacOS), the application programs that you use (e.g. Firefox, an office suite) and the data that you create, download or receive (documents, MP3 files, email).
A hard disc drive consists of several main components. The first is one or more thin discs that spin at anything from 3650 to 15000 RPM. The slower speeds - 3650 up to 5400 or occasionally 7200 - are used on laptops, mainly to minimise power consumption and noise. Speeds of 5400 and 7200 and occasionally 10000 RPM (10k) are used on desktop computers where power consumption is not so much of an issue and noise can be more easily suppressed. Drives running at 10k and 15k are generally used only in server computers. The 15k drives especially are very noisy and generate quite a bit of heat. It goes without saying that the higher the rotational speed of the disc, all else being equal, the better the performance.

Although there is no physical manifestation of them, the surface of a disc is treated as having a number of tracks - concentric circles (unlike a vinyl disc which has a single spiral). If there is more than one recording surface (usually there are at least two), then the tracks in corresponding positions on each surface are said to form a cylinder (in fact, you can have a cylinder with one track in it but this is now virtually unseen). The disc assembly is rotated at a constant speed by an electronically controlled motor. any slight variations in speed are fed back to the electronics by sensors and this enables them to keep track of exactly where the disc is in it's rotation and to correct the speed.
The second major component is the head assembly. This consists of record/playback heads mounted on very low mass but very rigid arms which can pivot so that the heads can be placed over any of the tracks. The pivot that the heads assembly swivels on is a genuine marvel of modern technological engineering, particularly as it is mass produced at such a low price. The head assembly is moved by what is known as a "voice coil". The term comes from loudspeaker manufacturing where the coil which moves the speaker's cone has been called a "voice coil", with some justification!, for around 100 years. The coil is mounted on the opposite side of the pivot from the arms carrying the heads. It is placed between two very powerful permanent magnets. Passing an electric current through the coil creates an electromagnetic force which moves the whole assembly on its pivot. Feedback from sensors allows the drive electronics to know exactly where the assembly is and how fast it is moving. This information is used to control the current in the coil to make the heads arrive at the the required track in the shortest possible time. This process is called "seeking".
The surfaces of the disc are coated with a very thin layer of magnetic material. This is then coated with one or more protective layers. When the disc is rotating, the heads (which are on tiny spring mounts on the end of the arms) "fly" above the surface of the disc at a distance of about 1/10th the diameter of a human hair. In fact, in some modern drives it is considerably less than this. The interaction between the disk surface, the tiny, specially shaped head and the air between them gives rise to aerodynamic forces which keep the head at exactly the required height for optimum reading & writing performance. These forces are considerably greater than the force of gravity so that a modern disc unit can run happily in virtually any orientation - vertical, horizontal etc.
Because of the tiny distance between the head and disc, any tiny dust particle present could easily get between them and force them apart. This could result in anything from some data being skipped to the head bouncing and scratching the disc. The latter is referred to as a "Head crash" and invariably results in permanent loss of recorded data and usually the need to replace the drive.
To write a single data bit to the disc, the drive electronics passes a tiny, precisely shaped pulse of current through the coil of the read/write head. This causes a small part of the disc coating to become magnetised in a particular orientation. In older drives, each bit was recorded with a N and a S pole along the direction of spin of the disc. Modern drives store data at a much greater density and in order to achieve this the bits are stored as tiny magnets which are perpendicular to the surface of the disc - one of the poles is beneath the other, within the magnetic layer. In practice, a single bit is never written and a complex waveform s generated by the drive in order to write a "block" of data.
Each track is subdivided into a number of blocks. The exact number varies with the size of the drive and the block size selected when you format the drive (but that's another story). Data is always read and written as a whole number of blocks. So, a block occupies an arc along a track. The blocks are numbered and that number (along with the cylinder and track numbers) is recorded in a part of the block that does not hold data. Each block is actually divided into three "fields" - Count, Key and Data. This allows the drive to check, after a seek, that it has indeed found the location on the disc that it was seeking and that it has the right size. These extra bits of information (Count and Key) plus some other housekeeping information and the gaps between the blocks, account for the difference between the nominal size of a disc drive (e.g. 80 GB) and the formatted size (e.g. 76 GB).
When the drive has to read data, it moves the head so that it passes over the area of the disc containing the required data. The combination of physical movement and they tiny magnetic fields on the disc cause a minuscule electric current to be generated in the coil of the read/write head. That current is first amplified by an integrated circuit which is as close to the head as can be arranged, in order to minimise signal loss due to long wires. The amplified signal is then passed to other circuitry which performs more amplification and conditioning of the signal before it is subject to Digital Signal Processing which recovers the recorded data. So, the controller circuit board on the drive is a fairly complex computer in its own right - it will often have two or three embedded processors: One for the interface to the host computer, another for the read/write processing and perhaps a third to control the spindle motor (the discs are mounted on the spindle - or axle).
A further article will explain how the data - which arrives at & comes from the read/write head as a stream of bits - gets transferred to the host computer (e.g. your ) and ends up as the collection of bytes which makes up, e.g., your Word document.

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