ATX

ATX (Advanced Technology eXtended) is a motherboard and power supply configuration specification developed by Intel in 1995 to improve on previous de facto standards like the AT design. It was the first major change in desktop computer enclosure, motherboard and power supply design in many years, improving standardization and interchangeability of parts. The specification defines the dimensions; the mounting points; the I/O panel; and the power and connector interfaces among a computer case, a motherboard, and a power supply.

This article is about the computer form factor. For other uses, see ATX (disambiguation).
An ATX motherboard
Comparison of some common motherboard form factors (pen for scale)

ATX is the most common motherboard design.[1] 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 is version 2.2.[2] The most recent ATX12V power supply unit specification is 2.53,[3] released in June 2020. 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 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 2022, the ATX design still remains the de facto standard for personal computers.

Connectors
ATX I/O plates for motherboard rear connectors

On the back of the computer case, some major changes were made to 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 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. If necessary, I/O plates can be replaced to suit a motherboard that is being fitted; the I/O plates are usually included with motherboards not designed for a particular computer. The computer will operate correctly without 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 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 the ATX specification was that it was last revised when power supplies were normally placed at the top, rather than the bottom, of 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 to make it convenient for top mounted power supplies. This makes it very difficult for cables from bottom mounted power supplies to reach, and commonly requires 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 reach or fail to reach, or are too stiff to make the bend, and extensions are commonly required due to this placement.

Variants
"EATX" redirects here. For the electronic automatic transaxle, see automatic transmission.
Main article: Computer form factor
ATX, Mini-ITX, and AT motherboard compatible dimensions and bore positions
ATX motherboard size comparison; rear is on left.
  microATX (244 × 244 mm)
  Standard ATX (305 × 244 mm)
Ultra ATX (9.6 x 14.4 In)
  Extended ATX (EATX) (305 × 330 mm)
  WTX (356 × 425 mm)

Several ATX-derived designs have been specified that use 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 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 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.[4]

Form factor Originated Date Max. size[lower-alpha 1]
width × depth		 Slots Notes
(typical usage, Market adoption, etc.)
ATX Intel 1995 12 × 9.6 in (305 × 244 mm) 7 Original, successor to AT motherboard
Proprietary, specific to crypto-mining specific motherboards ? 2011 12 × 8 in (305 × 203 mm) 3 3 double-slot add-in cards with 1 slots of free space in between
SSI CEB SSI ? 12 × 10.5 in (305 × 267 mm) 7 Compact Electronics Bay
SSI MEB SSI 2011 16.2 × 13 in (411 × 330 mm) 12 Midrange Electronics Bay
SSI EEB SSI ? 12 × 13 in (305 × 330 mm) 7 Enterprise Electronics Bay
SSI TEB SSI ? 12 × 10.5 in (305 × 267 mm) 7 Thin Electronics Bay, for rack-mount, has board component height specification
microATX Intel 1997 9.6 × 9.6 in (244 × 244 mm) 4 Fits in ATX, and EATX cases.
FlexATX Intel 1997 9 × 7.5 in (229 × 191 mm) 3
Extended ATX (standard) Supermicro / Asus ? 12 × 13 in (305 × 330 mm) 7 Screw holes not completely compatible with some ATX cases. Designed for dual CPUs, and quad double slot video cards.
Extended ATX (commonly) Un­known ? 12 × 10.1 in (305 × 257 mm)
12 × 10.4 in (305 × 264 mm)
12 × 10.5 in (305 × 267 mm)
12 × 10.7 in (305 × 272 mm)		 7 ATX pattern screw holes
EE-ATX Supermicro ? 13.68 × 13 in (347 × 330 mm) 7 Enhanced Extended ATX
Ultra ATX Foxconn 2008 14.4 × 9.6 in (366 × 244 mm) 10 Intended for multiple double-slot video cards, and dual CPUs.
XL-ATX EVGA 2009 13.5 × 10.3 in (343 × 262 mm) 9
XL-ATX Gigabyte 2010 13.58 x 10.31 in (345 x 262 mm) 7
XL-ATX MSI 2010 13.6 × 10.4 in (345 × 264 mm) 7
WTX Intel 1998 14 × 16.75 in (356 × 425 mm). 9 Discontinued 2008
Mini-ITX VIA 2001 6.7 x 6.7in (170 × 170 mm). 1 Originally designed for home theatre or other fanless applications
Mini-DTX AMD 2007 8 × 6.7 in (203 × 170 mm) 2 Derived from Mini-ITX and DTX
BTX Intel 2004 12.8 × 10.5 in (325 × 267 mm) 7 Canceled 2006. Also micro, nano, and pico variants. Not generally compatible with ATX mounting.
HPTX EVGA 2010 13.6 × 15 in (345 × 381 mm) 6 Dual processors, 12 RAM slots
SWTX Supermicro 2006 16.48 × 13 in (419 × 330 mm)
and others		 5 Quad processors, not compatible with ATX mounting

Although true E-ATX 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 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.[5] The firm called the new 14.4 × 9.6 in (366 × 244 mm) design of this motherboard "Ultra ATX"[6] in its CES 2008 showing. Also unveiled during the January 2008 CES was the Lian Li Armorsuit PC-P80 case with 10 slots designed for the motherboard.[7]

The name "XL-ATX" has been used by at least three companies in different ways:

  • In September 2009, EVGA Corporation had already released a 13.5 × 10.3 in (343 × 262 mm) "XL-ATX" motherboard as its EVGA X58 Classified 4-Way SLI.[8]
  • Gigabyte Technology launched another XL-ATX motherboard, with model number GA-X58A-UD9 in 2010 measuring at 13.6 × 10.3 in (345 × 262 mm), and GA-X79-UD7 in 2011 measuring at 12.8 × 10.0 in (324 × 253 mm). In April 2010, Gigabyte announced its 12.8 × 9.6 in (325 × 244 mm) GA-890FXA-UD7 motherboard that allowed all seven slots to be moved downward by one slot position. The added length could have allowed placement of up to eight expansion slots, but the top slot position is vacant on this particular model.
  • MSI released MSI X58 Big Bang in 2010, MSI P67 Big Bang Marshal in 2011, MSI X79 Xpower Big Bang 2 in 2012 and MSI Z87 Xpower in 2013 all of them are 13.6 × 10.4 in (345 × 264 mm). Although these boards have room for additional expansion slots (9 and 8 total, respectively), all three provide only seven expansion connectors; the topmost positions are left vacant to provide more room for the CPU, chipset and associated cooling.

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 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).[9]

See also

Notes
  1. For boards which take expansion slots, the length of the expansion card aligns with the depth of the system board. The case may support cards longer than the depth of the mainboard.

References
  1. Mark, Soper; Prowse, David; Mueller, Scott (September 2012). Authorized Cert Guide: CompTIA A+. Pearson Education. ISBN 978-0-7897-4850-8.
  2. "ATX Specification - Version 2.2" (PDF). Archived from the original (PDF) on 2012-07-25. Retrieved April 4, 2014.
  3. "Power Supply Design Guide for Desktop Platform Form Factors, Revision 003". Intel. June 2020. Retrieved February 22, 2021.{{cite web}}: CS1 maint: url-status (link)
  4. Scott Mueller, Upgrading and Repairing PCs, Eleventh Edition, Que Books, 1999, ISBN 0-7897-1903-7, page 1255
  5. "Foxconn F1 Motherboard Prototype". Hardwaresecrets.com. Archived from the original on 24 October 2014. Retrieved 18 November 2014.
  6. Thomas Soderstrom (13 January 2008). "Foxconn Reveals X48, Ultra ATX, and Shamino". Tom's Hardware. Retrieved 18 November 2014.
  7. "Lian Li Armorsuit PC-P80R Spider Edition". TechPowerUp. Retrieved 18 November 2014.
  8. "The New 4-Way SLI Platform Has Arrived!". Evga.com. Retrieved 18 November 2014.
  9. "EVGA Corporation Super Record 2". Evga.com. Retrieved 18 November 2014.
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