Saturday, August 7, 2010
Phrasing it
The form website is the most commonly used form, but "Web site" and "web site" are also used. Some academia, some large book publishers, and dictionaries such as Merriam-Webster use "Web site". This is because "Web" is not a generic term, but rather, it is a short form of the proper name World Wide Web. As with many newly-created terms, it may take some time before a common phrasing is finalized. This debate also applies to the related terms such as web page, webmaster, and webcam.
The Reuters style guide uses "website", making no mention of any other spelling.[4]
The Chicago Manual of Style recommends "Web site" for formal use and "website" for informal use [5]
The AP Stylebook from The Associated Press previously[6] used "Web site", but announced in April 2010 it would change to "website"[7].
The Canadian Oxford Dictionary and the Canadian Press Style book lists "website" as the preferred phrase. The Oxford English Dictionary began using "website" as its standardized form in 2004.[8]
Garner's Modern American Usage acknowledges that "website" is the standard form [9].
Bill Walsh, the copy chief of The Washington Post's national desk, argues for using "Web site" in his books, Lapsing into a Comma and The Elephants of Style, and on his website, The Slot.[10] However, the Washington Post itself uses "website". [11]
Among major internet technology companies, Microsoft uses "website" and occasionally "web site" [12][13][14], Apple uses "website" [15], and Google uses "website".[16].
The Reuters style guide uses "website", making no mention of any other spelling.[4]
The Chicago Manual of Style recommends "Web site" for formal use and "website" for informal use [5]
The AP Stylebook from The Associated Press previously[6] used "Web site", but announced in April 2010 it would change to "website"[7].
The Canadian Oxford Dictionary and the Canadian Press Style book lists "website" as the preferred phrase. The Oxford English Dictionary began using "website" as its standardized form in 2004.[8]
Garner's Modern American Usage acknowledges that "website" is the standard form [9].
Bill Walsh, the copy chief of The Washington Post's national desk, argues for using "Web site" in his books, Lapsing into a Comma and The Elephants of Style, and on his website, The Slot.[10] However, the Washington Post itself uses "website". [11]
Among major internet technology companies, Microsoft uses "website" and occasionally "web site" [12][13][14], Apple uses "website" [15], and Google uses "website".[16].
Product- or service-based sites
Some websites derive revenue by offering products or services for sale. In the case of e-commerce websites, the products or services may be purchased at the website itself, by entering credit card or other payment information into a payment form on the site. While most business websites serve as a shop window for existing brick and mortar businesses, it is increasingly the case that some websites are businesses in their own right; that is, the products they offer are only available for purchase on the web.
Websites occasionally derive income from a combination of these two practices. For example, a website such as an online auctions website may charge the users of its auction service to list an auction, but also display third-party advertisements on the site, from which it derives further income.
Websites occasionally derive income from a combination of these two practices. For example, a website such as an online auctions website may charge the users of its auction service to list an auction, but also display third-party advertisements on the site, from which it derives further income.
Software systems
There is a wide range of software systems, such as ANSI C servlets), Java Server Pages (JSP), the PHP and Perl programming languages, ASP.NET, Active Server Pages (ASP), YUMA and ColdFusion (CFML) that are available to generate dynamic web systems and dynamic sites. Sites may also include content that is retrieved from one or more databases or by using XML-based technologies such as RSS.
Static content may also be dynamically generated either periodically, or if certain conditions for regeneration occur (cached) in order to avoid the performance loss of initiating the dynamic engine on a per-user or per-connection basis.
Plug ins are available to expand the features and abilities of web browsers, which use them to show active content, such as Microsoft Silverlight, Adobe Flash, Adobe Shockwave or applets written in Java. Dynamic HTML also provides for user interactivity and realtime element updating within web pages (i.e., pages don't have to be loaded or reloaded to effect any changes), mainly using the Document Object Model (DOM) and JavaScript, support which is built-in to most modern web browsers.
Turning a website into an income source is a common practice for web developers and website owners. There are several methods for creating a website business which fall into two broad categories, as defined below.
Static content may also be dynamically generated either periodically, or if certain conditions for regeneration occur (cached) in order to avoid the performance loss of initiating the dynamic engine on a per-user or per-connection basis.
Plug ins are available to expand the features and abilities of web browsers, which use them to show active content, such as Microsoft Silverlight, Adobe Flash, Adobe Shockwave or applets written in Java. Dynamic HTML also provides for user interactivity and realtime element updating within web pages (i.e., pages don't have to be loaded or reloaded to effect any changes), mainly using the Document Object Model (DOM) and JavaScript, support which is built-in to most modern web browsers.
Turning a website into an income source is a common practice for web developers and website owners. There are several methods for creating a website business which fall into two broad categories, as defined below.
Purpose of dynamic websites
The main purpose of a dynamic website is automation. A dynamic website can operate more effectively, be built more efficiently and is easier to maintain, update and expand. It is much simpler to build a template and a database than to build hundreds or thousands of individual, static HTML web pages.
Dynamic content
The second type is a website with dynamic content displayed in plain view. Variable content is displayed dynamically on the fly based on certain criteria, usually by retrieving content stored in a database.
A website with dynamic content refers to how its messages, text, images and other information are displayed on the web page, and more specifically how its content changes at any given moment. The web page content varies based on certain criteria, either pre-defined rules or variable user input. For example, a website with a database of news articles can use a pre-defined rule which tells it to display all news articles for today's date. This type of dynamic website will automatically show the most current news articles on any given date. Another example of dynamic content is when a retail website with a database of media products allows a user to input a search request for the keyword Beatles. In response, the content of the web page will spontaneously change the way it looked before, and will then display a list of Beatles products like CD's, DVD's and books.
A website with dynamic content refers to how its messages, text, images and other information are displayed on the web page, and more specifically how its content changes at any given moment. The web page content varies based on certain criteria, either pre-defined rules or variable user input. For example, a website with a database of news articles can use a pre-defined rule which tells it to display all news articles for today's date. This type of dynamic website will automatically show the most current news articles on any given date. Another example of dynamic content is when a retail website with a database of media products allows a user to input a search request for the keyword Beatles. In response, the content of the web page will spontaneously change the way it looked before, and will then display a list of Beatles products like CD's, DVD's and books.
Dynamic code
The first type is a web page with dynamic code. The code is constructed dynamically on the fly using active programming language instead of plain, static HTML.
A website with dynamic code refers to its construction or how it is built, and more specifically refers to the code used to create a single web page. A dynamic web page is generated on the fly by piecing together certain blocks of code, procedures or routines. A dynamically-generated web page would call various bits of information from a database and put them together in a pre-defined format to present the reader with a coherent page. It interacts with users in a variety of ways including by reading cookies recognizing users' previous history, session variables, server side variables etc., or by using direct interaction (form elements, mouse overs, etc.). A site can display the current state of a dialogue between users, monitor a changing situation, or provide information in some way personalized to the requirements of the individual user.
A website with dynamic code refers to its construction or how it is built, and more specifically refers to the code used to create a single web page. A dynamic web page is generated on the fly by piecing together certain blocks of code, procedures or routines. A dynamically-generated web page would call various bits of information from a database and put them together in a pre-defined format to present the reader with a coherent page. It interacts with users in a variety of ways including by reading cookies recognizing users' previous history, session variables, server side variables etc., or by using direct interaction (form elements, mouse overs, etc.). A site can display the current state of a dialogue between users, monitor a changing situation, or provide information in some way personalized to the requirements of the individual user.
Dynamic website
A dynamic website is one that changes or customizes itself frequently and automatically, based on certain criteria.
Dynamic websites can have two types of dynamic activity: Code and Content. Dynamic code is invisible or behind the scenes and dynamic content is visible or fully displayed.
Dynamic websites can have two types of dynamic activity: Code and Content. Dynamic code is invisible or behind the scenes and dynamic content is visible or fully displayed.
Static website
A static website is one that has web pages stored on the server in the format that is sent to a client web browser. It is primarily coded in Hypertext Markup Language (HTML).
Simple forms or marketing examples of websites, such as classic website, a five-page website or a brochure website are often static websites, because they present pre-defined, static information to the user. This may include information about a company and its products and services via text, photos, animations, audio/video and interactive menus and navigation.
This type of website usually displays the same information to all visitors. Similar to handing out a printed brochure to customers or clients, a static website will generally provide consistent, standard information for an extended period of time. Although the website owner may make updates periodically, it is a manual process to edit the text, photos and other content and may require basic website design skills and software.
In summary, visitors are not able to control what information they receive via a static website, and must instead settle for whatever content the website owner has decided to offer at that time.
They are edited using four broad categories of software:
Text editors, such as Notepad or TextEdit, where content and HTML markup are manipulated directly within the editor program
WYSIWYG offline editors, such as Microsoft FrontPage and Adobe Dreamweaver (previously Macromedia Dreamweaver), with which the site is edited using a GUI interface and the final HTML markup is generated automatically by the editor software
WYSIWYG online editors which create media rich online presentation like web pages, widgets, intro, blogs, and other documents.
Template-based editors, such as Rapidweaver and iWeb, which allow users to quickly create and upload web pages to a web server without detailed HTML knowledge, as they pick a suitable template from a palette and add pictures and text to it in a desktop publishing fashion without direct manipulation of HTML code.
Simple forms or marketing examples of websites, such as classic website, a five-page website or a brochure website are often static websites, because they present pre-defined, static information to the user. This may include information about a company and its products and services via text, photos, animations, audio/video and interactive menus and navigation.
This type of website usually displays the same information to all visitors. Similar to handing out a printed brochure to customers or clients, a static website will generally provide consistent, standard information for an extended period of time. Although the website owner may make updates periodically, it is a manual process to edit the text, photos and other content and may require basic website design skills and software.
In summary, visitors are not able to control what information they receive via a static website, and must instead settle for whatever content the website owner has decided to offer at that time.
They are edited using four broad categories of software:
Text editors, such as Notepad or TextEdit, where content and HTML markup are manipulated directly within the editor program
WYSIWYG offline editors, such as Microsoft FrontPage and Adobe Dreamweaver (previously Macromedia Dreamweaver), with which the site is edited using a GUI interface and the final HTML markup is generated automatically by the editor software
WYSIWYG online editors which create media rich online presentation like web pages, widgets, intro, blogs, and other documents.
Template-based editors, such as Rapidweaver and iWeb, which allow users to quickly create and upload web pages to a web server without detailed HTML knowledge, as they pick a suitable template from a palette and add pictures and text to it in a desktop publishing fashion without direct manipulation of HTML code.
Organized by function, a website may be
a personal website
a commercial website
a government website
a non-profit organization website
It could be the work of an individual, a business or other organization, and is typically dedicated to some particular topic or purpose. Any website can contain a hyperlink to any other website, so the distinction between individual sites, as perceived by the user, may sometimes be blurred.
Websites are written in, or dynamically converted to, HTML (Hyper Text Markup Language) and are accessed using a software interface classified as a user agent. Web pages can be viewed or otherwise accessed from a range of computer-based and Internet-enabled devices of various sizes, including desktop computers, laptops, PDAs and cell phones.
A website is hosted on a computer system known as a web server, also called an HTTP server, and these terms can also refer to the software that runs on these systems and that retrieves and delivers the web pages in response to requests from the website users. Apache is the most commonly used web server software (according to Netcraft statistics) and Microsoft's Internet Information Server (IIS) is also commonly used.
a personal website
a commercial website
a government website
a non-profit organization website
It could be the work of an individual, a business or other organization, and is typically dedicated to some particular topic or purpose. Any website can contain a hyperlink to any other website, so the distinction between individual sites, as perceived by the user, may sometimes be blurred.
Websites are written in, or dynamically converted to, HTML (Hyper Text Markup Language) and are accessed using a software interface classified as a user agent. Web pages can be viewed or otherwise accessed from a range of computer-based and Internet-enabled devices of various sizes, including desktop computers, laptops, PDAs and cell phones.
A website is hosted on a computer system known as a web server, also called an HTTP server, and these terms can also refer to the software that runs on these systems and that retrieves and delivers the web pages in response to requests from the website users. Apache is the most commonly used web server software (according to Netcraft statistics) and Microsoft's Internet Information Server (IIS) is also commonly used.
History
The World Wide Web (WWW) was created in 1989 by CERN physicist Tim Berners-Lee.[2] On 30 April 1993, CERN announced that the World Wide Web would be free to use for anyone.[3] Before the introduction of HTML and HTTP, other protocols such as file transfer protocol and the gopher protocol were used to retrieve individual files from a server. These protocols offer a simple directory structure which the user navigates and chooses files to download. Documents were most often presented as plain text files without formatting or were encoded in word processor formats.
Website
A website (also spelled Web site;[1] officially styled website by the AP Stylebook)[citation needed] is a collection of related web pages, images, videos or other digital assets that are addressed relative to a common Uniform Resource Locator (URL), often consisting of only the domain name, or the IP address, and the root path ('/') in an Internet Protocol-based network. A web site is hosted on at least one web server, accessible via a network such as the Internet or a private local area network.
A web page is a document, typically written in plain text interspersed with formatting instructions of Hypertext Markup Language (HTML, XHTML). A web page may incorporate elements from other websites with suitable markup anchors.
Web pages are accessed and transported with the Hypertext Transfer Protocol (HTTP), which may optionally employ encryption (HTTP Secure, HTTPS) to provide security and privacy for the user of the web page content. The user's application, often a web browser, renders the page content according to its HTML markup instructions onto a display terminal.
All publicly accessible websites collectively constitute the World Wide Web.
The pages of a website can usually be accessed from a simple Uniform Resource Locator (URL) called the homepage. The URLs of the pages organize them into a hierarchy, although hyperlinking between them conveys the reader's perceived site structure and guides the reader's navigation of the site.
Some websites require a subscription to access some or all of their content. Examples of subscription websites include many business sites, parts of news websites, academic journal websites, gaming websites, message boards, web-based e-mail, social networking websites, websites providing real-time stock market data, and websites providing various other services (e.g. websites offering storing and/or sharing of images, files and so forth).
A web page is a document, typically written in plain text interspersed with formatting instructions of Hypertext Markup Language (HTML, XHTML). A web page may incorporate elements from other websites with suitable markup anchors.
Web pages are accessed and transported with the Hypertext Transfer Protocol (HTTP), which may optionally employ encryption (HTTP Secure, HTTPS) to provide security and privacy for the user of the web page content. The user's application, often a web browser, renders the page content according to its HTML markup instructions onto a display terminal.
All publicly accessible websites collectively constitute the World Wide Web.
The pages of a website can usually be accessed from a simple Uniform Resource Locator (URL) called the homepage. The URLs of the pages organize them into a hierarchy, although hyperlinking between them conveys the reader's perceived site structure and guides the reader's navigation of the site.
Some websites require a subscription to access some or all of their content. Examples of subscription websites include many business sites, parts of news websites, academic journal websites, gaming websites, message boards, web-based e-mail, social networking websites, websites providing real-time stock market data, and websites providing various other services (e.g. websites offering storing and/or sharing of images, files and so forth).
Friday, August 6, 2010
Software
The method by which the software physically controls the fan is usually PWM (see above). Many companies now provide software to control fan speeds on their motherboards under Microsoft Windows.
AOpen motherboards can use "SilentTEK".
ASUS motherboards can use "Q-Fan".[2]
MSI motherboards can use "Core Center".
Universal abit motherboards can use "μGuru".
Gigabyte motherboards can use "EasyTune 6".
Intel desktop boards (older socket 478 etc) use "Active Monitor" and "Desktop Control Centre".[3][4]
Intel desktop boards (newer socket 775 etc) use "Desktop Utilities".[5]
Dell Inspiron/Latitude/Precision computers can use "I8kfanGUI".[6]
Various computers can use the freeware "SpeedFan".[7]
Computers running Linux can use lm sensors.[8]
AOpen motherboards can use "SilentTEK".
ASUS motherboards can use "Q-Fan".[2]
MSI motherboards can use "Core Center".
Universal abit motherboards can use "μGuru".
Gigabyte motherboards can use "EasyTune 6".
Intel desktop boards (older socket 478 etc) use "Active Monitor" and "Desktop Control Centre".[3][4]
Intel desktop boards (newer socket 775 etc) use "Desktop Utilities".[5]
Dell Inspiron/Latitude/Precision computers can use "I8kfanGUI".[6]
Various computers can use the freeware "SpeedFan".[7]
Computers running Linux can use lm sensors.[8]
Fan speed controllers
Another method, popular with gamers[citation needed], is the manual fan speed controller. They can be mounted in an expansion slot, a 5.25" or 3.5" drive bay or come built into the computer's case. Using switches or knobs, attached fans can have their speeds adjusted by one of the above methods.
Pulse-width modulation
Pulse-width modulation (PWM) is a common method of controlling fans. Modern computer motherboard PWM control when used with multi-core CPUs reads data from Digital Temperature Sensors on each core of the CPU.
Unlike the linear methods above that are based on voltage loss, PWM switches the input voltage between (nearly) fully on and fully off. This means there is practically no voltage or power loss and associated heat output. PWM controller can be a relatively small, low-power and cool-running, albeit complex, component that doesn't require heavy duty resistors, diodes or transistors and associated heatsinking.
Unlike the linear methods above that are based on voltage loss, PWM switches the input voltage between (nearly) fully on and fully off. This means there is practically no voltage or power loss and associated heat output. PWM controller can be a relatively small, low-power and cool-running, albeit complex, component that doesn't require heavy duty resistors, diodes or transistors and associated heatsinking.
Voltmodding
Voltmodding describes the practice of varying the voltage fed to a component; in this case, a computer fan. This can be achieved by connecting the ground wire of the fan to the +5V rail and the positive wire to the +12V rail of a typical PC power supply to achieve a theoretical +7V (positive seven volts). However, this is a potentially risky method: the parts on the +5V power line might be exposed to overvoltage in case of a short in the fan. A less common variation is to increase the voltage to the fan by connecting the ground wire to a -12V rail (located on the motherboard ATX connector) and the positive wire to the +12V rail, producing a total of +24V.[1]
Diodes
diode in series with the fan will reduce the voltage being outputted to the fan. You can use a zener diode (select one for the desired voltage drop) or a silicon diode (Produce the required voltage drop by connecting multiple diodes in series. Each diode reduces the voltage by approximately 0.75 volts.)
Resistors
Resistors are the simplest method of reducing fan noise, but they add to the heat generated inside the computer case. They need to be of the appropriate power rating (i.e. higher than the fan). For variable fan control, potentiometers could be used along with a transistor such as a MOSFET whose output voltage is controlled by the potentiometer. It is possible to use a rheostat instead.
Linear voltage regulation
A standard cooling fan is essentially a bladed DC motor. By varying the voltage input across the acceptable range for a fan, the speed of the fan will increase (to added voltage) and decrease (to reduced voltage). A faster fan, obviously, means more air moved, and thus a higher heat exchange rate. There are a few ways to perform this regulation.
Thermostatic
In this style of fan control, the fan is either on or off. A system thermistor checks the temperature inside the chassis, and if it detects a temperature outside of range, it spins the fans up to maximum. When the temperature drops below a threshold again, the fans are turned back off. This control method reduces power requirements during periods of low usage, but when the system is operating at capacity, the fan noise can become a problem again.
No control
The simplest method of fan control is simply to leave the fan on all the time. This creates quite a bit of noise and increases power requirements, but keeps the system the coolest.
Fan types
Common cooling fans will have either two, three, or four pins on the connector.
Two-pin fans operate either as an on/off fan, or can be controlled by varying the voltage.
Three-pin fans add a tachometer reporting wire so the controlling system can measure the actual speed.
Four-pin fans add a fourth wire to control fan speed using PWM (Pulse-width modulation.)
Two-pin fans operate either as an on/off fan, or can be controlled by varying the voltage.
Three-pin fans add a tachometer reporting wire so the controlling system can measure the actual speed.
Four-pin fans add a fourth wire to control fan speed using PWM (Pulse-width modulation.)
Need for fan control
As modern PCs grow more powerful so do their requirements for electrical power. Computers convert most of this electrical power into heat generated by all major components.
Some early generation PCs did not need active ventilation. Power supplies eventually needed forced cooling, and soon took up the duty of cooling the rest of the PC with the ATX standard. The byproduct of increased heat generation is that the fan(s) need to move increasing amounts air and thus, need to be more powerful. Since they must move more air through the same area of space, fans will naturally become more noisy.
In fact, if one installs extra fans in a PC case, the noise levels can reach 70 dB. Since fan noise increases exponentially to the fan rotation speed, reducing rotations per minute (RPM) by a small amount potentially means a reduction in fan noise.[citation needed] This must be done cautiously, as excessive reduction in speed may cause components to overheat and be damaged. If done properly fan noise can be drastically reduced.
Some early generation PCs did not need active ventilation. Power supplies eventually needed forced cooling, and soon took up the duty of cooling the rest of the PC with the ATX standard. The byproduct of increased heat generation is that the fan(s) need to move increasing amounts air and thus, need to be more powerful. Since they must move more air through the same area of space, fans will naturally become more noisy.
In fact, if one installs extra fans in a PC case, the noise levels can reach 70 dB. Since fan noise increases exponentially to the fan rotation speed, reducing rotations per minute (RPM) by a small amount potentially means a reduction in fan noise.[citation needed] This must be done cautiously, as excessive reduction in speed may cause components to overheat and be damaged. If done properly fan noise can be drastically reduced.
Need for fan control
As modern PCs grow more powerful so do their requirements for electrical power. Computers convert most of this electrical power into heat generated by all major components.
Some early generation PCs did not need active ventilation. Power supplies eventually needed forced cooling, and soon took up the duty of cooling the rest of the PC with the ATX standard. The byproduct of increased heat generation is that the fan(s) need to move increasing amounts air and thus, need to be more powerful. Since they must move more air through the same area of space, fans will naturally become more noisy.
In fact, if one installs extra fans in a PC case, the noise levels can reach 70 dB. Since fan noise increases exponentially to the fan rotation speed, reducing rotations per minute (RPM) by a small amount potentially means a reduction in fan noise.[citation needed] This must be done cautiously, as excessive reduction in speed may cause components to overheat and be damaged. If done properly fan noise can be drastically reduced.
Some early generation PCs did not need active ventilation. Power supplies eventually needed forced cooling, and soon took up the duty of cooling the rest of the PC with the ATX standard. The byproduct of increased heat generation is that the fan(s) need to move increasing amounts air and thus, need to be more powerful. Since they must move more air through the same area of space, fans will naturally become more noisy.
In fact, if one installs extra fans in a PC case, the noise levels can reach 70 dB. Since fan noise increases exponentially to the fan rotation speed, reducing rotations per minute (RPM) by a small amount potentially means a reduction in fan noise.[citation needed] This must be done cautiously, as excessive reduction in speed may cause components to overheat and be damaged. If done properly fan noise can be drastically reduced.
Fan control
Fan control is the management of the rotational speed of an electric fan, typically a computer fan, to provide adequate cooling while lowering noise.
Modular power supplies
A modular power supply is a relatively new approach to cabling, allowing users to omit unused cables. Whereas a conventional design has numerous cables permanently connected to the power supply, a modular power supply provides connectors at the power supply end, allowing unused cables to be detached from the power supply, producing less clutter, a neater appearance and less interference with airflow. It also makes it possible to supply a wider variety of cables, providing different lengths of Serial ATA power connectors instead of Molex connectors.
While modular cabling can help reduce case clutter, they have often been criticized for creating electrical resistance. Some third party websites that do power supply testing have confirmed that the quality of the connector, the age of the connector, the number of times it was inserted/removed, and various other variables such as dust can all raise resistance. However, this is somewhat inconsequential as the amount of this resistance in a good connector is small compared to the resistance generated by the length of the wire itself.[9]
While modular cabling can help reduce case clutter, they have often been criticized for creating electrical resistance. Some third party websites that do power supply testing have confirmed that the quality of the connector, the age of the connector, the number of times it was inserted/removed, and various other variables such as dust can all raise resistance. However, this is somewhat inconsequential as the amount of this resistance in a good connector is small compared to the resistance generated by the length of the wire itself.[9]
Small facts to consider
Life span is usually measured in mean time between failures (MTBF). Higher MTBF ratings are preferable for longer device life and reliability. Quality construction consisting of industrial grade electrical components and/or a larger or higher speed fan can help to contribute to a higher MTBF rating by keeping critical components cool, thus preventing the unit from overheating. Overheating is a major cause of PSU failure. MTBF value of 100,000 hours is not uncommon.
Power supplies may have passive or active power factor correction (PFC). Passive PFC is a simple way of increasing the power factor by putting a coil in series with the primary filter capacitors. Active PFC is more complex and can achieve higher PF, up to 99%.
In computer power supplies that have more than one +12V power rail, it is preferable for stability reasons to spread the power load over the 12V rails evenly to help avoid overloading one of the rails on the power supply.
Multiple 12V power supply rails are separately current limited as a safety feature; they are not generated separately. Despite widespread belief to the contrary, this separation has no effect on mutual interference between supply rails.
The ATX12V 2.x and EPS12V power supply standards defer to the IEC 60950 standard, which requires that no more than 240 volt-amps be present between any two accessible points. Thus, each wire must be current-limited to no more than 20 A; typical supplies guarantee 18 A without triggering the current limit. Power supplies capable of delivering more than 18 A at 12 V connect wires in groups to two or more current sensors which will shut down the supply if excess current flows. Unlike a fuse or circuit breaker, these limits reset as soon as the overload is removed.
Because of the above standards, almost all high-power supplies claim to implement separate rails, however this claim is often false; many omit the necessary current-limit circuitry,[5] both for cost reasons and because it is an irritation to customers.[1] (The lack is sometimes advertised as a feature under names like "rail fusion" or "current sharing".)
When the computer is powered down but the power supply is still on, it can be started remotely via Wake-on-LAN and Wake-on-Ring or locally via Keyboard Power ON (KBPO) if the motherboard supports it.
Early PSUs used a conventional (heavy) step-down transformer, but most modern computer power supplies are a type of switched-mode power supply (SMPS) with a ferrite-cored High Frequency transformer.
Computer power supplies may have short circuit protection, overpower (overload) protection, overvoltage protection, undervoltage protection, overcurrent protection, and over temperature protection.
Some power supplies come with sleeved cables, which is aesthetically nicer, makes wiring easier and cleaner and have less detrimental effect on airflow.
There is a popular misconception that a greater power capacity (watt output capacity) is always better. Since supplies are self-certified, a manufacturer's claims may be double or more what is actually provided.[6][7] Although a too-large power supply will have an extra margin of safety as far as not over-loading, a larger unit is often less efficient at lower loads (under 20% of its total capability) and therefore will waste more electricity than a more appropriately sized unit. Additionally, computer power supplies generally do not function properly if they are too lightly loaded. Under no-load conditions they may shut down or malfunction.
Another popular misconception is that the greater the total watt capacity is, the more suitable the power supply becomes for higher-end graphics cards. The most important factor for judging a PSUs suitability for certain graphics cards is the PSUs total 12V output, as it is that voltage on which modern graphics cards operate. If the total 12V output stated on the PSU is higher than the suggested minimum of the card, then that PSU can fully supply the card. It is however recommended that a PSU should not just cover the graphics cards' demands, as there are other components in the PC that depend on the 12V output, including the CPU and disk drives.
Power supplies can feature magnetic amplifiers or double-forward converter circuit design.
Energy efficiency
Computer power supplies are generally about 70–75% efficient.[3] That means in order for a 75% efficient power supply to produce 75 W of DC output it would require 100 W of AC input and dissipate the remaining 25 W in heat. Higher-quality power supplies can be over 80% efficient; higher energy efficient PSU's waste less energy in heat, and requires less airflow to cool, and as a result will be quieter. Google's server power supplies are more than 90% efficient.[2] HP's server power supplies have reached 94% efficiency.[4] Standard PSUs sold for server workstations have around 90% efficiency, as of 2010.
It's important to match the capacity of a power supply to the power needs of the computer. The energy efficiency of power supplies drops significantly at low loads. Efficiency generally peaks at about 50-75% load. The curve varies from model to model (examples of how this curve looks can be seen on test reports of energy efficient models found on the 80 PLUS website). As a rule of thumb for standard power supplies it is usually appropriate to buy a supply such that the calculated typical consumption of one's computer is about 60% of the rated capacity of the supply provided that the calculated maximum consumption of the computer does not exceed the rated capacity of the supply. Note that advice on overall power supply ratings often given by the manufacturer of single component, typically graphics cards, should be treated with great skepticism. These manufacturers wish to minimise support issues due to under rating the power supply and are willing to advise customers to overrate it to avoid this.
Various initiatives are underway to improve the efficiency of computer power supplies. Climate savers computing initiative promotes energy saving and reduction of greenhouse gas emissions by encouraging development and use of more efficient power supplies. 80 PLUS certifies power supplies that meet certain efficiency criteria, and encourages their use via financial incentives. On top of that the businesses end up using less electricity to cool the PSU and the computer's themselves and thus save an initially large sum(i.e. incentive + saved electricity = higher profit).
It's important to match the capacity of a power supply to the power needs of the computer. The energy efficiency of power supplies drops significantly at low loads. Efficiency generally peaks at about 50-75% load. The curve varies from model to model (examples of how this curve looks can be seen on test reports of energy efficient models found on the 80 PLUS website). As a rule of thumb for standard power supplies it is usually appropriate to buy a supply such that the calculated typical consumption of one's computer is about 60% of the rated capacity of the supply provided that the calculated maximum consumption of the computer does not exceed the rated capacity of the supply. Note that advice on overall power supply ratings often given by the manufacturer of single component, typically graphics cards, should be treated with great skepticism. These manufacturers wish to minimise support issues due to under rating the power supply and are willing to advise customers to overrate it to avoid this.
Various initiatives are underway to improve the efficiency of computer power supplies. Climate savers computing initiative promotes energy saving and reduction of greenhouse gas emissions by encouraging development and use of more efficient power supplies. 80 PLUS certifies power supplies that meet certain efficiency criteria, and encourages their use via financial incentives. On top of that the businesses end up using less electricity to cool the PSU and the computer's themselves and thus save an initially large sum(i.e. incentive + saved electricity = higher profit).
Servers
Some web servers use a single-voltage 12 volt power supply. All other voltages are generated by voltage regulator modules on the motherboard.[2]
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