A mousepad or mousemat is a surface for placing and moving a computer mouse. A mousepad enhances the usability of the mouse compared to using a mouse directly on a table by providing a surface to allow it to measure movement and without jitter; some mousepads increase ergonomics by providing a padded wrist rest. During a 1968 presentation by Douglas Engelbart marking the public debut of a mouse, Engelbart used a control console designed by Jack Kelley of Herman Miller that included a keyboard and an inset portion used as a support area for the mouse. According to Kelley and stated by Alex Pang, Kelley designed the first mousepad a year in 1969. Details of a mousepad designed by Armando M. Fernandez were published in the Xerox Disclosure Journal in 1979 with the description: CRT Cursor Control Mechanism Pad To assist the operation of a cathode ray tube pointer 10 wherein a metal ball is rolled on a hard surface, the disclosed pad may be utilized. A resilient, rubber-like material 12 is bonded or otherwise attached to a hard base material 14 which keeps the rubber-like material flat.
The base has four rubber-like pads 16 on the opposite side from the resilient material to refrain the pad from sliding on the surface of a table, for instance. By 1982, most users of the Xerox ball mouse were using "special pads" to increase the friction of the ball; the first commercial manufacturer of mousepads was Moustrak, founded by Bob McDermand. The company began gaining traction when Apple decided to distribute its mousepads, featuring the Apple logo, to computer stores in the United States. Moustrak signed licensing deals with Disney and LucasFilm, advertised in magazines including MacWorld. However, by the end of the 1980s, lower cost mousepads turned the product into a commodity; the Oxford English Dictionary tracks the term mouse pad to the 24 August 1983, publication of InfoWorld, the predominantly British term mousemat to 17 October 1989, in the publication 3D. The three most important benefits of the introduction of the mousepad were higher speed, more precision, comfort for the user.
A secondary benefit was keeping the desk or table surface from being scratched and worn by continuous hand and mouse rubbing motion. Another benefit was reduction of the collection of debris under the mouse, which resulted in reduced jitter of the pointer on the display; when optical mice, which use image sensors to detect movement, were first introduced into the market, they required special mousepads with optical patterns printed on them. Modern optical mice can function to an acceptable degree of accuracy on plain paper and other surfaces. However, some optical mouse users may prefer a mousepad for comfort and accuracy, to prevent wear to the desk or table surface. A variety of mousepads exist with many different textured surfaces to fit various types of mouse technologies. Vinyl board cover, because of its natural adhesive properties, was a popular mousepad surface around 1980. After the steel mouse ball was given a silicone rubber surface, the popular fabric-surface mousepad was found to be the most appropriate.
It helped keep the rubberized roller-ball surface cleaner and gave better tracking and accuracy than just a desk surface. Such surfaces collected dirt, deposited onto the internal rollers that picked off ball movement. Dirty rollers caused erratic pointer movement on the screen. Early types of optical mice have the problem of not working well on transparent or reflective surfaces such as glass or polished wood; these surfaces, which include desk and table surfaces, cause jitter and loss of tracking on the display pointer as the mouse moves over these reflective spots. The use of mousepads with precision surfaces eliminates spot jitter effects of older and/or low-quality optical mice. Newer generations of mousepads incorporate a wireless charging system, allowing certain wireless mice to be used without the need to replace or recharge batteries. Modern mousepads are made of lesser density rubber composites with fabric bonded to the upper surface. However, many other types of material have been used, including fabric, recycled rubber tires, silicone rubber, glass, wood, aluminum and stainless steel.
High-quality gaming mats are made from plastic, aluminum or high-tech fibers. Media related to mousepads at Wikimedia Commons
A computer case known as a computer chassis, system unit, CPU, or cabinet, is the enclosure that contains most of the components of a personal computer. Cases are constructed from steel or aluminium. Plastic is sometimes used, other materials such as glass and Lego bricks have appeared in home-built cases. Cases can come in many different sizes; the size and shape of a computer case is determined by the form factor of the motherboard, since it is the largest component of most computers. Personal computer form factors specify only the internal dimensions and layout of the case. Form factors for rack-mounted and blade servers may include precise external dimensions as well, since these cases must themselves fit in specific enclosures. For example, a case designed for an ATX motherboard and power supply may take on several external forms such as a vertical tower, a flat desktop or pizza box. Full-size tower cases are larger in volume than desktop cases, with more room for drive bays, expansion slots, custom or all-in-one water cooling solutions.
Desktop cases—and mini-tower cases under about 46 cm high—are popular in business environments where space is at a premium. The most popular form factor for desktop computers is ATX, although microATX and small form factors have become popular for a variety of uses. In the high-end segment the unofficial and loosely defined XL-ATX specification appeared around 2009, it extends the length of the mainboard to accommodate four graphics cards with dual-slot coolers. Some XL-ATX mainboards increase the mainboard's width as well, to allow more space for the CPU, Memory PWM, in some cases, a second CPU socket. While the market share of these exotic high-end mainboards is low all high-end cases and many mainstream cases support XL-ATX; as of 2018, no major motherboard manufacturer has made an XL-ATX board for several years. Companies like In Win Development, Shuttle Inc. and AOpen popularized small cases, for which FlexATX was the most common motherboard size. As of 2010 Mini ITX has replaced FlexATX as the most common small form factor mainboard standard.
The latest mini ITX mainboards from Asus, Gigabyte, MSI, ASRock and Foxconn offer the same feature set as full size mainboards. High-end mini ITX mainboards support standard desktop CPUs, use standard memory DIMM sockets, feature a full size PCI-E 16× slot with support for the fastest graphics cards, although some instead use a PCI, or PCIe slot of less than 16 lanes; this allows customers to build a fledged high-end computer in a smaller case. Apple Inc. has produced the Mac Mini computer, similar in size to a standard CD-ROM drive, many manufacturers offer mini-ITX cases of similar size for low-wattage CPUs with integrated graphics. Tower cases are categorized as mini-tower, midi-tower, mid-tower or full-tower; the terms are subjective and inconsistently defined by different manufacturers. Full tower cases are 56 cm or more in height and intended to stand on the floor, they can have anywhere from six to ten externally accessible drive bays, although in recent years, this has shifted to offering better airflow in the front by moving the drive bays elsewhere in the case.
The ratio of external to internal bays is shifting, however, as computing technology moves from floppy disks and CD-ROMs to large capacity hard drives, USB flash drives, network-based solutions. The full tower case was developed to house file servers which would be tasked with serving data from expensive CD-ROM databases which held more data than the hard drives available, but are moving now towards being showpiece display cases with custom water cooling and tempered glass. Hence many full tower cases include locking doors and other physical security features to prevent theft of the discs; this is a high-end case doesn't include security features. Mid-tower cases are smaller, about 46 cm high with two to four external bays. A mini-tower case will have only one or two external bays; the marketing term midi-tower has come into use referring to cases smaller than mid-tower but larger than mini-tower with two to three external bays. Outside of the United States the term is used interchangeably with mid-tower.
The computer case is sometimes erroneously referred to as the "CPU" or "hard drive". Computer cases include sheet metal enclosures for a power supply unit and drive bays, as well as a rear panel that can accommodate peripheral connectors protruding from the motherboard and expansion slots. Most cases have a power button or switch, a reset button, LEDs to indicate power, hard drive activity, network activity in some models; some cases include built-in I/O ports on the front of the case. Such a case will include the wires needed to connect these ports and indicators to the motherboard; the motherboard is screwed to the case along its largest face, which could be the bottom or the side of the case depending on the form factor and orientation. Form factors such as ATX provide a back panel with cut-out holes to expose I/O ports provided by integrated peripherals, as well as expansion
A DIMM or dual in-line memory module comprises a series of dynamic random-access memory integrated circuits. These modules are mounted on a printed circuit board and designed for use in personal computers and servers. DIMMs began to replace SIMMs as the predominant type of memory module as Intel P5-based Pentium processors began to gain market share. While the contacts on SIMMs on both sides are redundant, DIMMs have separate electrical contacts on each side of the module. Another difference is that standard SIMMs have a 32-bit data path, while standard DIMMs have a 64-bit data path. Since Intel's Pentium, many processors have a 64-bit bus width, requiring SIMMs installed in matched pairs in order to populate the data bus; the processor would access the two SIMMs in parallel. DIMMs were introduced to eliminate this disadvantage. Variants of DIMM slots support DDR, DDR2, DDR3 and DDR4 RAM. Common types of DIMMs include the following: 70 to 200 pins 72-pin SO-DIMM, used for FPM DRAM and EDO DRAM 100-pin DIMM, used for printer SDRAM 144-pin SO-DIMM, used for SDR SDRAM 168-pin DIMM, used for SDR SDRAM 172-pin MicroDIMM, used for DDR SDRAM 184-pin DIMM, used for DDR SDRAM 200-pin SO-DIMM, used for DDR SDRAM and DDR2 SDRAM 200-pin DIMM, used for FPM/EDO DRAM in some Sun workstations and servers.201 to 300 pins 204-pin SO-DIMM, used for DDR3 SDRAM 214-pin MicroDIMM, used for DDR2 SDRAM 240-pin DIMM, used for DDR2 SDRAM, DDR3 SDRAM and FB-DIMM DRAM 244-pin MiniDIMM, used for DDR2 SDRAM 260-pin SO-DIMM, used for DDR4 SDRAM 260-pin SO-DIMM, with different notch position than on DDR4 SO-DIMMs, used for UniDIMMs that can carry either DDR3 or DDR4 SDRAM 278-pin DIMM, used for HP high density SDRAM.
288-pin DIMM, used for DDR4 SDRAM On the bottom edge of 168-pin DIMMs there are two notches, the location of each notch determines a particular feature of the module. The first notch is the DRAM key position, which represents RFU, unbuffered DIMM types; the second notch is the voltage key position, which represents 5.0 V, 3.3 V, RFU DIMM types. DDR, DDR2, DDR3 and DDR4 all have different pin counts, different notch positions; as of August, 2014, DDR4 SDRAM is a modern emerging type of dynamic random access memory with a high-bandwidth interface, has been in use since 2013. It is the higher-speed successor to DDR, DDR2 and DDR3. DDR4 SDRAM is neither forward nor backward compatible with any earlier type of random access memory because of different signalling voltages, timings, as well as other differing factors between the technologies and their implementation. A DIMM's capacity and other operational parameters may be identified with serial presence detect, an additional chip which contains information about the module type and timing for the memory controller to be configured correctly.
The SPD EEPROM connects to the System Management Bus and may contain thermal sensors. ECC DIMMs are those that have extra data bits which can be used by the system memory controller to detect and correct errors. There are numerous ECC schemes, but the most common is Single Error Correct, Double Error Detect which uses an extra byte per 64-bit word. ECC modules carry a multiple of 9 instead of a multiple of 8 chips. Sometimes memory modules are designed with two or more independent sets of DRAM chips connected to the same address and data buses. Ranks that share the same slot, only one rank may be accessed at any given time; the other ranks on the module are deactivated for the duration of the operation by having their corresponding CS signals deactivated. DIMMs are being manufactured with up to four ranks per module. Consumer DIMM vendors have begun to distinguish between single and dual ranked DIMMs. After a memory word is fetched, the memory is inaccessible for an extended period of time while the sense amplifiers are charged for access of the next cell.
By interleaving the memory, sequential memory accesses can be performed more because sense amplifiers have 3 cycles of idle time for recharging, between accesses. DIMMs are referred to as "single-sided" or "double-sided" to describe whether the DRAM chips are located on one or both sides of the module's printed circuit board. However, these terms may cause confusion, as the physical layout of the chips does not relate to how they are logically organized or accessed. JEDEC decided that the terms "dual-sided", "double-sided", or "dual-banked" were not correct when applied to registered DIMMs. Most DIMMs are built" × 8" memory chips with nine chips per side. In the case of "×4" registered DIMMs, the data width per side is 36 bits. In this case, the two-sided module is single-ranked. For "×8" registered DIMMs, each side is 72 bits wide, so the memory controller only addresses one side at a time; the above example applies to ECC memory that stores 72 bits instead of the more common 64. There would be one extra chip per group of eight, not counted.
For various technologies, there are certain bus and device clock frequencies that are standa
A headset combines a headphone with a microphone. Headsets are made with either a double-earpiece. Headsets provide the equivalent functionality of a telephone handset but with handsfree operation, they have many uses including in call centers and other telephone-intensive jobs and for anybody wishing to have both hands free during a telephone conversation. Telephone headsets use 150-ohm loudspeakers with a narrower frequency range than those used for entertainment. Stereo computer headsets, on the other hand, use 32-ohm speakers with a broader frequency range. Headsets are available in double-earpiece designs. Single-earpiece headsets are known as monaural headsets. Double-earpiece headsets may use the same audio channel for both ear-pieces. Monaural headsets free up one ear. Telephone headsets are monaural for double-earpiece designs, because telephone offers only single-channel input and output. For computer or other audio applications, where the sources offer two-channel output, stereo headsets are the norm.
Virtual surround. This type of headset uses one on each ear cup, to create surround sound. Virtual surround headsets tend to have higher-end driver components which experts and consumers believe to be more durable, as well as have larger speakers which deliver more powerful and dynamic sound quality. Virtual surround headset achieves surround sound by using external or internal pre-amplifier or mix-amplifier modules, as well as several different algorithms, to convert stereo or surround sound signals into surround sound; the sound is divided and sectioned so as to deliver it in such a way that it creates an auditory landscape, thereby producing surround sound. The microphone arm of headsets may be of the voice tube type. External microphone designs have the microphone housed in the front end of the microphone arm. Voicetube designs are called internal microphone design, have the microphone housed near the earpiece, with a tube carrying sound to the microphone. Most external microphone designs are of either noise-canceling type.
Noise-canceling microphone headsets use a bi-directional microphone as elements. A bi-directional microphone's receptive field has two angles only, its receptive field is limited to the direct opposite back of the microphone. This creates an "8" shape field, this design is the best method for picking up sound only from a close proximity of the user, while not picking up most surrounding noises. Omni-directional microphones pick up the complete 360-degree field, which may include much extraneous noise. Standard headsets with a headband worn over the head are known as over-the-head headsets. Headsets with headbands going over the back of the user's neck are known as backwear-headsets or behind-the-neck headsets. Headsets worn over the ear with a soft ear-hook are known as over-the-ear headsets or earloop headsets. Convertible headsets are designed so that users can change the wearing method by re-assembling various parts. Telephone headsets connect to a fixed-line telephone system. A telephone headset functions by replacing the handset of a telephone.
Headsets for standard corded telephones are fitted with a standard 4P4C called an RJ-9 connector. Headsets are available with 2.5mm jack sockets for many DECT phones and other applications. Cordless bluetooth headsets are available and used with mobile telephones. Headsets are used for telephone-intensive jobs, in particular by call centre workers, they are used by anyone wishing to hold telephone conversations with both hands free. Headset compatibility and pin alignmentNot all telephone headsets are compatible with all telephone models; because headsets connect to the telephone via the standard handset jack, the pin-alignment of the telephone handset may be different from the default pin-alignment of the telephone headset. To ensure a headset can properly pair with a telephone, telephone adapters or pin-alignment adapters are available; some of these adapters provide mute function and switching between handset and headset. Telephone amplifiersFor older models of telephones, the headset microphone impedance is different from that of the original handset, requiring a telephone amplifier to impedance-match the telephone headset.
A telephone amplifier provides basic pin-alignment similar to a telephone headset adapter, but it offers sound amplification for the microphone as well as the loudspeakers. Most models of telephone amplifiers offer volume control for the loudspeaker as well as a microphone, mute function and switching between handset and headset. Telephone amplifiers are powered through AC adapters. Quick disconnecting cableMost telephone headsets have a Quick Disconnect cable, allowing fast and easy disconnection of the headset from the telephone without having to remove the headset. Handset lifterA Handset lifter is a device that automatically lifts or replaces a handset off/on a telephone, it is connected to a wireless headset and allows cordless headset use on technically primitive desk phones. Some phones only have a mechanical means of switchhook operation; the lifter allows cordless headsets to be used remotely with such phones. The phone user presses the appropriate headset button to either terminate a call.
The headset's base station's interface with the handset lifter will take the appropriate action - lift or replace the handset. The use
A computer mouse is a hand-held pointing device that detects two-dimensional motion relative to a surface. This motion is translated into the motion of a pointer on a display, which allows a smooth control of the graphical user interface; the first public demonstration of a mouse controlling a computer system was in 1968. Wired to a computer, many modern mice are cordless, relying on short-range radio communication with the connected system. Mice used a ball rolling on a surface to detect motion, but modern mice have optical sensors that have no moving parts. In addition to moving a cursor, computer mice have one or more buttons to allow operations such as selection of a menu item on a display. Mice also feature other elements, such as touch surfaces and "wheels", which enable additional control and dimensional input; the earliest known publication of the term mouse as referring to a computer pointing device is in Bill English's July 1965 publication, "Computer-Aided Display Control" originating from its resemblance to the shape and size of a mouse, a rodent, with the cord resembling its tail.
The plural for the small rodent is always "mice" in modern usage. The plural of a computer mouse is "mouses" and "mice" according to most dictionaries, with "mice" being more common; the first recorded plural usage is "mice". The term computer mouses may be used informally in some cases. Although, the plural of mouse is mice, the two words have undergone a differentiation through usage; the trackball, a related pointing device, was invented in 1946 by Ralph Benjamin as part of a post-World War II-era fire-control radar plotting system called Comprehensive Display System. Benjamin was working for the British Royal Navy Scientific Service. Benjamin's project used analog computers to calculate the future position of target aircraft based on several initial input points provided by a user with a joystick. Benjamin felt that a more elegant input device was needed and invented what they called a "roller ball" for this purpose; the device was patented in 1947, but only a prototype using a metal ball rolling on two rubber-coated wheels was built, the device was kept as a military secret.
Another early trackball was built by British electrical engineer Kenyon Taylor in collaboration with Tom Cranston and Fred Longstaff. Taylor was part of the original Ferranti Canada, working on the Royal Canadian Navy's DATAR system in 1952. DATAR was similar in concept to Benjamin's display; the trackball used four disks to pick up two each for the X and Y directions. Several rollers provided mechanical support; when the ball was rolled, the pickup discs spun and contacts on their outer rim made periodic contact with wires, producing pulses of output with each movement of the ball. By counting the pulses, the physical movement of the ball could be determined. A digital computer calculated the tracks and sent the resulting data to other ships in a task force using pulse-code modulation radio signals; this trackball used a standard Canadian five-pin bowling ball. It was not patented. Douglas Engelbart of the Stanford Research Institute has been credited in published books by Thierry Bardini, Paul Ceruzzi, Howard Rheingold, several others as the inventor of the computer mouse.
Engelbart was recognized as such in various obituary titles after his death in July 2013. By 1963, Engelbart had established a research lab at SRI, the Augmentation Research Center, to pursue his objective of developing both hardware and software computer technology to "augment" human intelligence; that November, while attending a conference on computer graphics in Reno, Engelbart began to ponder how to adapt the underlying principles of the planimeter to X-Y coordinate input. On November 14, 1963, he first recorded his thoughts in his personal notebook about something he called a "bug," which in a "3-point" form could have a "drop point and 2 orthogonal wheels." He wrote that the "bug" would be "easier" and "more natural" to use, unlike a stylus, it would stay still when let go, which meant it would be "much better for coordination with the keyboard."In 1964, Bill English joined ARC, where he helped Engelbart build the first mouse prototype. They christened the device the mouse as early models had a cord attached to the rear part of the device which looked like a tail, in turn resembled the common mouse.
As noted above, this "mouse" was first mentioned in print in a July 1965 report, on which English was the lead author. On 9 December 1968, Engelbart publicly demonstrated the mouse at what would come to be known as The Mother of All Demos. Engelbart never received any royalties for it, as his employer SRI held the patent, which expired before the mouse became used in personal computers. In any event, the invention of the mouse was just a small part of Engelbart's much larger project of augmenting human intellect. Several other experimental pointing-devices developed for Engelbart's oN-Line System exploited different body movements – for example, head-mounted devices attached to the chin or nose – but the mouse won out because of its speed and convenience; the first mouse, a bulky device used two potentiometers perpendicular to each other and connected to wheels: the rotation of each wheel translated into motion along one axis. At the time of the "Mother of All Demos", Engelbart's group had been using their second generation, 3-button mouse for about a year.
On October 2, 1968, a mouse device named Rollkugel (German for "rolling bal
Taoyuan is a special municipality in northwestern Taiwan, neighboring New Taipei City, Hsinchu County, Yilan County. Taoyuan District is the seat of the municipal government and which, along with Zhongli District, forms a large metropolitan area. Taoyuan developed from a satellite city of Taipei metropolitan area to become the fourth-largest metropolitan area, fifth-largest populated city in Taiwan. Since commuting to the Taipei metropolitan area is easy, Taoyuan has seen the fastest population growth of all cities in Taiwan. "Taoyuan" means "peach garden" in Chinese. The city is home to tech company headquarters. Taoyuan International Airport, which serves the capital and the rest of northern Taiwan, is located in this city; the city of Taoyuan has been elevated to special municipality status since 2014 from the original Taoyuan County. At the same time, the former county-administered city of Taoyuan was promoted to Taoyuan District within the new municipality. In ancient times, the Taoyuan plateau was the home of the Taiwanese plains aborigines.
In prehistory, the Ketagalan people settled in Nankan. In the early years of Dutch colonization, Spanish colonization, Zheng He of the Ming Dynasty, there were no large-scale cultivation or industrial activities. During the Qing era, a number of people from Fujian Province and Guangdong province began to immigrate into present-day Taoyuan to develop and farm the land, they planted peach trees, when bloomed in spring, were so beautiful that the people named the land Toahong. In November 1901, under Japanese rule, a local administrative office, Toshien Chō, was established in the area, renamed Tōen Chō in 1905. In 1920, the Tōen area was incorporated into Shinchiku Prefecture. During the Japanese era, the staged migration policy caused Taoyuan to develop into a city with a variety of cultures. For example and worship paths symbolized cultural systems. Butokuden were used to represent military systems, the old Taoyuan City Office signified political systems. In 1950, Taoyuan County was established by the Republic of China government.
On 21 April 1971, Taoyuan City was made the county seat of Taoyuan County. It had 1 urban township and 6 rural townships. Being located at the edge of the Greater Taipei region, this caused some structural and lifestyle changes within Taiwanese society. Trade prosperity in recent years and the proliferation of job opportunities helped Taoyuan develop into a major economic district in northern Taiwan and the population has increased since. On February 16, 1998, China Airlines Flight 676 crashed in Taoyaun City near Chiang Kai-shek International Airport, killing all 196 people on board and seven more on the ground. On December 25, 2014, Taoyuan County was reorganized into the special municipality of Taoyuan City. Taoyuan is located 40 km southwest of Taipei, in northern Taiwan, occupies 1,220 km2, it is made up of interconnected mountains and plateaus. Its shape has a long and narrow southeast-to-northwest trend, with the southeast in the Xueshan Range and the far end on the shores of the Taiwan Strait.
There are many irrigation ponds at Taoyuan Plateau, which caused Taoyuan to earn the nickname "Thousand-pond Township". Taoyuan has a humid subtropical climate, with mild to warm winters and hot summers, typical of northern Taiwan; as of the rest of Taiwan, the Hoklo are one of the largest ethnic groups of Taoyuan, most of whom live in northern Taoyuan, which comprises most northern districts of the city, including Bade, Dayuan and Luzhu, the city seat of government, Taoyuan District. The Hakka are the second-largest ethnic group in the city after the Hoklo, most of them residing in southern Taoyuan, which includes Zhongli, Yangmei, Longtan and Xinwu districts. With more than 785,000 Hakka people, Taoyuan hosts the largest Hakka population among all of Taiwan's administrative divisions. After the Chinese Civil War, many people from mainland China settled in the then-Taoyuan County after the retreat of the nationalist government in 1949. Most of them live in military dependents' villages in Zhongli and Guishan.
Longgang is well known for its immigrants from Yunnan. Most Taiwanese aborigines in the city live in Fuxing District, with most of them belonging to the Atayal people. Taoyuan is one of the Taiwan's top technological cities. High-tech companies including Quanta, MiTAC, Nanya Technology, HTC, CPT and AU Optronics have all opted to build or expand their factories in Taoyuan. Taoyuan has now become a bastion of electronics and semiconductor manufacturing. Over 200 of Taiwan's top 500 manufacturing companies have factories in Taoyuan. Taoyuan has led Taiwan in terms of industrial output for nine straight years. There are now 29 industrial areas with 3,696 ha of non-urban industrial land and 3,131 ha of urban industrial land. There are over 6,827 ha of land available for factories and industrial use in the city, representing the fact that Taoyuan's development bureau is based on industry and commerce. There are 9 sites for mixed industrial-commercial use, the most of any county and city in Taiwan. On March 26, 2010, China
A computer fan is any fan inside, or attached to, a computer case used for active cooling. Fans are used to draw cooler air into the case from the outside, expel warm air from inside, move air across a heat sink to cool a particular component. Both axial and sometimes centrifugal fans are used in computers. Computer fans come in standard sizes, are powered and controlled using 3- or 4-pin fan connectors; as processors, graphics cards, RAM and other components in computers have increased in speed and power consumption, the amount of heat produced by these components as a side-effect of normal operation has increased. These components need to be kept within a specified temperature range to prevent overheating, instability and damage leading to a shortened component lifespan. While in earlier personal computers it was possible to cool most components using natural convection, many modern components require more effective active cooling. To cool these components, fans are used to move heated air away from the components and draw cooler air over them.
Fans attached to components are used in combination with a heatsink to increase the area of heated surface in contact with the air, thereby improving the efficiency of cooling. Fan control is not always an automatic process. A computer's BIOS can control the speed of the built-in fan system for the computer. A user can supplement this function with additional cooling components or connect a manual fan controller with knobs that set fans to different speeds. In the IBM compatible PC market, the computer's power supply unit always uses an exhaust fan to expel warm air from the PSU. Active cooling on CPUs started to appear on the Intel 80486, by 1997 was standard on all desktop processors. Chassis or case fans one exhaust fan to expel heated air from the rear and optionally an intake fan to draw cooler air in through the front, became common with the arrival of the Pentium 4 in late 2000. A third vent fan in the side of the PC located over the CPU, is common; the graphics processing unit on most modern graphics cards requires a heatsink and one or more fans.
In some cases, the northbridge chip on the motherboard has another fan. Other components such as the hard drives and RAM may be cooled, though as of 2012 this remains unusual, it is not uncommon to find five or more fans in a modern PC. Fans are used to move air through the computer case; the components inside the case can not dissipate heat efficiently. Case fans may be placed as intake fans, drawing cooler outside air in through the front or bottom of the chassis, or exhaust fans, expelling warm air through the top or rear; some ATX tower cases have one or more additional vents and mounting points in the left side panel where one or more fans may be installed to blow cool air directly onto the motherboard components and expansion cards, which are among the largest heat sources. Standard axial case fans are 60, 80, 92, 120, 140, 200 and 220 mm in width and length; as case fans are the most visible form of cooling on a PC, decorative fans are available and may be lit with LEDs, made of UV-reactive plastic, and/or covered with decorative grilles.
Decorative fans and accessories are popular with case modders. Air filters are used over intake fans, to prevent dust from entering the case and clogging up the internal components. Heatsinks are vulnerable to being clogged up, as the insulating effect of the dust will degrade the heatsink's ability to dissipate heat. While the power supply contains a fan with few exceptions, it is not to be used for case ventilation; the hotter the PSU's intake air is, the hotter the PSU gets. As the PSU temperature rises, the conductivity of its internal components decrease. Decreased conductivity means that the PSU will convert more of the input electric energy into thermal energy; this cycle of increasing temperature and decreased efficiency continues until the PSU either overheats, or its cooling fan is spinning fast enough to keep the PSU adequately supplied with comparatively cool air. The PSU is bottom-mounted in modern PCs, having its own dedicated intake and exhaust vents, preferably with a dust filter in its intake vent.
Used to cool the CPU heatsink. Effective cooling of a concentrated heat source such as a large-scale integrated circuit requires a heatsink, which may be cooled by a fan. Used to cool the heatsink of the graphics processing unit or the memory on graphics cards; these fans were not necessary on older cards because of their low power dissipation, but most modern graphics cards designed for 3D graphics and gaming need their own dedicated cooling fans. Some of the higher powered cards can produce more heat than the CPU, so effective cooling is important. Since 2010, graphics cards have been released with either axial fans, or a centrifugal fan known as a blower, turbo or squirrel cage fan. Used to cool the heatsink of the northbridge of a motherboard's chipset; as more features of the chipset are integrated into the central processing unit, the role of the chipset has been reduced and the heat generation reduced also. Fans may be mounted next to or onto a hard disk drive for cooling purposes. Hard drives can produce considerable heat over time, are heat-sensitive components that should not operat