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48-677: ATX is a form factor for personal computer motherboards and power supplies. ATX or AT-X may also refer to: ATX ATX is the most common motherboard design. Other standards for smaller boards (including microATX , FlexATX , nano-ITX , and mini-ITX ) usually keep the basic rear layout but reduce the size of the board and the number of expansion slots. Dimensions of a full-size ATX board are 12 × 9.6 in (305 × 244 mm), which allows many ATX chassis to accept microATX boards. The ATX specifications were released by Intel in 1995 and have been revised numerous times since. The most recent ATX motherboard specification

96-574: A 12 V rail, while it was done by a 5 V rail on older PCs (before the Pentium ;4). The power demands of PCI Express were incorporated in ATX12V 2.0 (introduced in February 2003), which defined quite different power distribution from ATX12V 1.x: This is a minor revision from June 2004. An errant reference for the −5 V rail was removed. Other minor changes were introduced. This

144-431: A 3.3 volt source, removing the need for motherboards to derive this voltage from the 5 V rail. Some motherboards, particularly those manufactured after the introduction of ATX but whilst LPX equipment was still in use, support both LPX and ATX PSUs. If using an ATX PSU for purposes other than powering an ATX motherboard, power can be fully turned on (it is always partly on to operate "wake-up" devices) by shorting

192-516: A full range of integrated peripherals (especially integrated graphics ), which may serve as the basis for small form factor and media center PCs. For example, the ASRock G31M-S motherboard (pictured right) features onboard Intel GMA graphics, HD Audio audio, and Realtek Ethernet (among others), thus freeing up the expansion slots that would have been used for a graphics card, sound card, and Ethernet card. In recent years, however, it

240-506: A large number of memory slots. In 2004, Intel announced the BTX (Balanced Technology eXtended) standard, intended as a replacement for ATX. While some manufacturers adopted the new standard, Intel discontinued any future development of BTX in 2006. As of 2024 , the ATX design still remains the de facto standard for personal computers. On the back of the computer case, some major changes were made to

288-576: A plate fitted, although there will be open gaps in the case which may compromise the EMI/RFI screening and allow ingress of dirt and random foreign bodies. Panels were made that allowed fitting an AT motherboard in an ATX case. Some ATX motherboards come with an integrated I/O plate. ATX also made the PS/2-style mini-DIN keyboard and mouse connectors ubiquitous. AT systems used a 5-pin DIN connector for

336-453: A power button that is directly connected to the system computer power supply (PSU). The general configuration is a double-pole latching mains voltage switch with the four pins connected to wires from a four-core cable. The wires are either soldered to the power button (making it difficult to replace the power supply if it failed) or blade receptacles were used. An ATX power supply is typically controlled by an electronic switch connected to

384-489: A rectangular area on the back of the system with an arrangement they could define themselves, though a number of general patterns depending on what ports the motherboard offers have been followed by most manufacturers. Cases are usually fitted with a snap-out panel, also known as an I/O plate or I/O shield, in one of the common arrangements. I/O plates are usually included with retail motherboards to allow installation in any suitable case. The computer will operate correctly without

432-796: A section about Climate Savers, updated recommended power supply configuration charts, and updated the cross-regulation graphs. This is the unofficial name given to the later revisions of the v2.31 specifications, published in May 2020 The ATX12V 2.4 specifications were published in August 2021. It is specified in Revision 1.31 of the 'Design Guide for Desktop Platform Form Factors', which names this as ATX12V version 2.4. The specifications for ATXV12 2.51 were released in September 2021 and introduced support for Alternative Low Power Mode (ALPM) which supersedes

480-428: A special cutout in the back plane for the cable to come in from behind and bend around the board, making insertion and wire management very difficult. Many power supply cables barely or fail to reach, or are too stiff to make the bend, and extensions are sometimes required due to this placement. Modern power supplies often have longer cables to alleviate this issue. Several ATX-derived designs have been specified that use

528-422: A standard system power supply, so the Pentium 4 established the practice of generating it with a DC-to-DC converter on the motherboard next to the processor, powered by the 4-pin 12 V connector. This is a minor revision from August 2000. The power on the 3.3 V rail was slightly increased and other smaller changes were made. A relatively minor revision from January 2002. The only significant change

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576-655: A two second delay for an improved user experience. The specifications for ATXV12 2.53 were released in December 2021 and constitute another minor update to the ATX standard. ATXV12 2.53 makes further recommendations on efficiency and references the Energy Star Computers Specification Version 8.0 which was finalized in April 2020. MicroATX In computer design, microATX (sometimes referred to as μATX , uATX or mATX )

624-490: Is 12 × 13 in (305 × 330 mm) most motherboard manufacturers also refer to motherboards with measurements 12 × 10.1 in (305 × 257 mm), 12 × 10.4 in (305 × 264 mm), 12 × 10.5 in (305 × 267 mm) and 12 × 10.7 in (305 × 272 mm) as E-ATX. While E-ATX and SSI EEB (Server System Infrastructure (SSI) Forum's Enterprise Electronics Bay (EEB)) share

672-558: Is a minor revision from March 2005. The power was slightly increased on all rails. Efficiency requirements changed: minimum 65% at light load, 72% at typical load, and 70% at full load. Introduced recommended minimum values of 75% at light load, 80% at typical load, and 77% at full load. Also released in March 2005 it includes corrections and specifies High Current Series wire terminals for 24-pin ATX motherboard and 4-pin +12 V power connectors. Effective March 2007. Recommended efficiency

720-651: Is a potential source of confusion. A number of manufacturers have added one to three additional expansion slots (at the standard 0.8 inch spacing) to the standard 12-inch ATX motherboard width. Form factors considered obsolete in 1999 included Baby-AT, full size AT, and the semi-proprietary LPX for low-profile cases. Proprietary motherboard designs such as those by Compaq, Packard-Bell, Hewlett Packard and others existed, and were not interchangeable with multi-manufacturer boards and cases. Portable and notebook computers and some 19-inch rackmount servers have custom motherboards unique to their particular products. Although true E-ATX

768-450: Is a standard motherboard form factor introduced in December 1997. The maximum size of a microATX motherboard is 9.6 × 9.6 in (244 × 244 mm). However, there are examples of motherboards using microATX designation despite having a smaller size of 244 × 205 mm (9.6 × 8.1 in). The standard ATX size is 25% longer, at 12 × 9.6 in (305 × 244 mm). microATX

816-588: Is common even for ATX boards to integrate all these components, as much of this functionality is contained in the typical northbridge – southbridge pair. In the DIY PC market, microATX motherboards in general are favored by cost-conscious buyers, where cost savings for the equivalent feature sets outweigh the added expandability of extra PCI/PCI Express slots provided by the full ATX versions. Since 2006, dual-GPU configurations became possible on microATX motherboards for high-end enthusiast gaming setups, further reducing

864-482: Is not a replacement for a current-limited bench laboratory DC power supply; instead it is better described as a bulk DC power supply . The original ATX specification called for a power supply to be located near to the CPU with the power supply fan drawing in cooling air from outside the chassis and directing it onto the processor. It was thought that in this configuration, cooling of the processor would be achievable without

912-400: Is primarily used to provide the negative supply voltage for RS-232 ports and is also used by one pin on conventional PCI slots primarily to provide a reference voltage for some models of sound cards . The 5 V SB supply is used to produce trickle power to provide the soft-power feature of ATX when a PC is turned off, as well as powering the real-time clock to conserve the charge of

960-493: Is version 2.2. The most recent ATX12V power supply unit specification is ATX 3.0 released in February 2022. EATX (Extended ATX) is a bigger version of the ATX motherboard with 12 × 13 in (305 × 330 mm) dimensions. While some dual CPU socket motherboards have been implemented in ATX, the extra size of EATX makes it the typical form factor for dual socket systems, and with sockets that support four or eight memory channels, for single socket systems with

1008-524: The +12 V Power Connector , this is commonly referred to as the P4 connector because this was first needed to support the Pentium 4 processor. Before the Pentium 4, processors were generally powered from the 5 V rail. Later processors operate at much lower voltages, typically around 1 V and some draw over 100 A. It is infeasible to provide power at such low voltages and high currents from

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1056-613: The CMOS battery . A −5 V output was originally required because it was supplied on the ISA bus; it was removed in later versions of the ATX standard, as it became obsolete with the removal of the ISA bus expansion slots (the ISA bus itself is still found in any computer which is compatible with the old IBM PC specification; e.g., not found in the PlayStation 4 ). Originally, the motherboard

1104-541: The Intel Skulltrail motherboard that could accommodate two Intel Core 2 Quad processors and has a total of seven PCI-E slots and 12 DDR3 RAM slots. The new design is dubbed "HPTX" and is 13.6 × 15 in (345 × 381 mm). The ATX specification requires the power supply to produce three main outputs, +3.3 V, +5 V and +12 V. Low-power −12 V and +5 V SB (standby) supplies are also required. The −12 V supply

1152-436: The "power-on" pin on the ATX connector (pin 16, green wire) to a black wire (ground), which is what the power button on an ATX system does. A minimum load on one or more voltages may be required (varies by model and vendor); the standard does not specify operation without a minimum load and a conforming PSU may shut down, output incorrect voltages, or otherwise malfunction, but will not be hazardous or damaged. An ATX power supply

1200-573: The 140 mm depth, is frequently varied, with depths of 160, 180, 200 and 230 mm used to accommodate higher power, larger fan and/or modular connectors. Original AT cases (flat case style) have an integrated power switch that protruded from the power supply and sits flush with a hole in the AT chassis. It utilizes a paddle-style DPST switch and is similar to the PC and PC-XT style power supplies. Later AT (so-called "Baby AT") and LPX style computer cases have

1248-589: The 4-pin connector as described below. Numbering of the ATX revisions may be a little confusing: ATX refers to the design, and goes up to version 2.2 in 2004 (with the 24 pins of ATX12V 2.0), while ATX12V describes only the PSU. For instance, ATX 2.03 is quite commonly seen on PSUs from 2000 and 2001 and often includes the P4 12V connector, even if the norm itself did not define it yet. The main changes and additions in ATX12V 1.0 (released in February 2000) were: Formally called

1296-423: The AT standard. Originally AT style cases had only a keyboard connector and expansion slots for add-on card backplates. Any other onboard interfaces (such as serial and parallel ports ) had to be connected via flying leads to connectors which were mounted either on spaces provided by the case or brackets placed in unused expansion slot positions. ATX allowed each motherboard manufacturer to put these ports in

1344-501: The ATX specification was that it was last revised when power supplies were normally placed at the top of many old computer cases rather than at the bottom, as with many modern computer cases. This has led to some problematic standard locations for ports, in particular the 4/8 pin CPU power, which is normally located along the top edge of the board, convenient for top-mounted power supplies. This makes it very difficult for cables from bottom-mounted power supplies to reach, and commonly requires

1392-586: The January 2008 CES was the Lian Li Armorsuit PC-P80 case with 10 slots designed for the motherboard. The name "XL-ATX" has been used by at least three companies in different ways: In 2010, EVGA Corporation released a new motherboard, the "Super Record 2", or SR-2, whose size surpasses that of the "EVGA X58 Classified 4-Way SLI". The new board is designed to accommodate two Dual QPI LGA1366 socket CPUs (e.g. Intel Xeon ), similar to that of

1440-669: The cable. The connector pin pitch is 4.20 mm (about one sixth of an inch). Four wires have special functions: Generally, supply voltages must be within ±5% of their nominal values at all times. The little-used negative supply voltages, however, have a ±10% tolerance. There is a specification for ripple in a 10 Hz–20 MHz bandwidth: The 20–24-pin Molex Mini-Fit Jr. has a power rating of, 9 amperes maximum per pin). As large server motherboards and 3D graphics cards have required progressively more and more power to operate, it has been necessary to revise and extend

1488-756: The keyboard and were generally used with serial port mice (although PS/2 mouse ports were also found on some systems). Many modern motherboards are phasing out the PS/2-style keyboard and mouse connectors in favor of the more modern Universal Serial Bus . Other legacy connectors that are slowly being phased out of modern ATX motherboards include 25-pin parallel ports and 9-pin RS-232 serial ports . In their place are onboard peripheral ports such as Ethernet , FireWire , eSATA , audio ports (both analog and S/PDIF ), video (analog D-sub , DVI , HDMI , or DisplayPort ), extra USB ports, and Wi-Fi. A notable issue with

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1536-505: The need of an active heatsink. This recommendation was removed from later specifications; modern ATX power supplies usually exhaust air from the case. ATX, introduced in late 1995, defined three types of power connectors: The power distribution specification defined that most of the PSU's power should be provided on 5 V and 3.3 V rails, because most of the electronic components (CPU, RAM, chipset, PCI, AGP and ISA cards) used 5 V or 3.3 V for power supply. The 12 V rail

1584-399: The power button on the computer case and allows the computer to be turned off by the operating system . In addition, many ATX power supplies have a manual switch on the back that also ensures no power is being sent to the components. When the switch on the power supply is turned off, the computer cannot be turned on with the front power button. The power supply's connection to the motherboard

1632-521: The same chipsets as full-size ATX boards, allowing them to use many of the same components. However, since microATX cases are typically much smaller than ATX cases, they usually have fewer expansion slots . Most modern ATX motherboards have a maximum of seven PCI or PCI-Express expansion slots, while microATX boards only have a maximum of four (four being the maximum permitted by the specification). In order to conserve expansion slots and case space, many manufacturers produce microATX motherboard with

1680-451: The same dimensions, the screw holes of the two standards do not all align; rendering them incompatible. In 2008, Foxconn unveiled a Foxconn F1 motherboard prototype, which has the same width as a standard ATX motherboard, but an extended 14.4" length to accommodate 10 slots. The firm called the new 14.4 × 9.6 in (366 × 244 mm) design of this motherboard "Ultra ATX" in its CES 2008 showing. Also unveiled during

1728-508: The same power supply, mountings and basic back panel arrangement, but set different standards for the size of the board and number of expansion slots. Standard ATX provides seven slots at 0.8 in (20 mm) spacing; the popular microATX size removes 2.4 inches (61 mm) and three slots, leaving four. Here width refers to the distance along the external connector edge, while depth is from front to rear. Note each larger size inherits all previous (smaller) colors area. AOpen has conflated

1776-444: The standard beyond the original 20-pin connector, to allow more current using multiple additional pins in parallel. The low circuit voltage is the restriction on power flow through each connector pin; at the maximum rated voltage, a single Mini-Fit Jr pin would be capable of 4800 watts. ATX power supplies generally have the dimensions of 150 × 86 × 140 mm (5.9 × 3.4 × 5.5 in), with

1824-508: The term Mini ATX with a more recent 15 × 15 cm (5.9 × 5.9 in) design. Since references to Mini ATX have been removed from ATX specifications since the adoption of microATX, the AOpen definition is the more contemporary term and the one listed above is apparently only of historical significance. This sounds contradictory to the now common Mini-ITX standard (17 × 17 cm (6.7 × 6.7 in)), which

1872-546: The traditional S3 power state . Windows 10 implements this functionality as Modern Standby . The specifications for ATXV12 2.52 were released in October 2021 introduces minor changes to the standard, most notably it requires power supply manufacturers to ensure power supplies with Alternative Low Power Mode (ALPM) support are able to withstand power cycles every 180 seconds (480 times per day or 175,200 per year). Power supply fans are also recommended to turn on with at least

1920-417: The width and height being the same as the preceding LPX (Low Profile eXtension) form factor (which are often incorrectly referred to as "AT" power supplies due to their ubiquitous use in later AT and Baby AT systems, even though the actual AT and Baby AT power supply form factors were physically larger) and share a common mounting layout of four screws arranged on the back side of the unit. That last dimension,

1968-475: Was changed from the older AT and LPX standards; AT and LPX had two similar connectors that could be accidentally interchanged by forcing the different keyed connectors into place, usually causing short-circuits and irreversible damage to the motherboard (the rule of thumb for safe operation was to connect the side-by-side connectors with the black wires together). ATX uses one large, keyed connector which can not be connected incorrectly. The new connector also provides

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2016-411: Was determined that it would be much cheaper and more practical to power most PC components from 12 V rails, instead of from 3.3 V and 5 V rails. In particular, PCI Express expansion cards take much of their power from the 12 V rail (up to 5.5 A), while the older AGP graphics cards took only up to 1 A on 12 V and up to 6 A on 3.3 V. The CPU is also driven by

2064-511: Was explicitly designed to be backward compatible with ATX. The mounting points of microATX motherboards are a subset of those used on full-size ATX boards, and the I/O panel is identical. Thus, microATX motherboards can be used in full-size ATX cases. Furthermore, most microATX motherboards generally use the same power connectors as ATX motherboards, thus permitting the use of full-size ATX power supplies with microATX boards. microATX boards often use

2112-447: Was increased to 80% (with at least 70% required) and the 12 V minimum load requirement was lowered. Higher efficiency generally results in less power consumption (and less waste heat ) and the 80% recommendation brings supplies in line with new Energy Star 4.0 mandates. The reduced load requirement allows compatibility with processors that draw very little power during startup. The absolute over-current limit of 240 VA per rail

2160-576: Was only used by computer fans and motors of peripheral devices (HDD, FDD, CD-ROM, etc.) While designing the Pentium 4 platform in 1999/2000, the standard 20-pin ATX power connector was found insufficient to meet increasing power-line requirements; the standard was significantly revised into ATX12V 1.0 (ATX12V 1.x is sometimes inaccurately called ATX-P4). ATX12V 1.x was also adopted by AMD Athlon XP and Athlon 64 systems. However, some early model Athlon XP and MP boards (including some server boards) and later model lower-end motherboards do not have

2208-455: Was powered by one 20-pin connector. An ATX power supply provides a number of peripheral power connectors and (in modern systems) two connectors for the motherboard: an 8-pin (or 4+4-pin) auxiliary connector providing additional power to the CPU and a main 24-pin power supply connector, an extension of the original 20-pin version. 20-pin Molex 39-29-9202 at the motherboard. 20-pin Molex 39-01-2200 at

2256-598: Was removed, allowing 12 V lines to provide more than 20 A per rail. This revision became effective in February 2008. It added a maximum allowed ripple/noise specification of 400 millivolts to the PWR_ON and PWR_OK signals, requires that the DC power must hold for more than 1 millisecond after the PWR_OK signal drops, clarified country-specific input line harmonic content and electromagnetic compatibility requirements, added

2304-426: Was that the −5 V rail was no longer required (it became optional). This voltage was required by the ISA bus, which is no longer present on almost all modern computers. Introduced in April 2003 (a month after 2.0). This standard introduced some changes, mostly minor. Some of them are: ATX12V 2.x brought a significant design change regarding power distribution. By analyzing the power demands of then-current PCs, it

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