ATX (Advanced Technology Extended) is a motherboard and power supply form factor and configuration specification developed by Intel. It aimed to improve on previous de facto standards such as the AT design. Originally released in July 1995, it was the first major change in desktop computer enclosure, motherboard and power supply design in many years, improving standardization and interchangeability of parts. ATX as a motherboard standard defines the dimensions of the board, the mounting points to connect with the computer case, the input/output (I/O) connector panel, expansion slot placement, and power supply connectors. ATX as a power supply form factor defines the dimensions, electrical current, and cables of a desktop power supply, designed specifically to be compatible with ATX and similar motherboards.
ATX is a commonly used motherboard and power supply hardware form factor for desktop computers. The ATX form factor defined a general mounting point placement and I/O panel size that smaller motherboards share (such as microATX, FlexATX, and Mini-ITX), making them backwards compatible in many computer cases.
Overview , ATX is the most common motherboard design. Other standards for smaller boards (including microATX, FlexATX, nano-ITX, and mini-ITX) 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 which means microATX boards fit in many ATX chassis. The ATX specifications were patented by David Dent at Intel and co-developed with Astec America, a major manufacturer of power supplies at the time. The inaugural version 1.0 of the ATX specification was unveiled by Intel in July 1995. Since then, ATX has been revised numerous times. The most recent ATX motherboard specification is version 2.2. The most recent ATX12V power supply unit specification is ATX 3.0 released in February 2022.
EATX, or E-ATX (Extended ATX), is a term that refers to motherboards larger than the ATX standard. Motherboards labeled E-ATX commonly share dimensions with the SSI-EEB (Server System Infrastructure - Enterprise Electronics Bay) standard (12 x 13 in), however, it is not a guarantee. 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 for single-socket systems with a large number of memory slots (or more than two memory channels).
BTX
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. , the ATX design still remains the standard for personal computers.
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.
The ATX standard specified a rectangular area on the back of the system where motherboard manufacturers can arrange ports any way they want. A number of general patterns (depending on which ports the motherboard offers) have been used 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 for installation in any suitable case. The computer will operate correctly without a plate fitted, but there will be open gaps in the case which may compromise the EMI/RFI screening and allow the ingress of dirt and random foreign bodies. Panels were made that fit 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 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 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.
Variants
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 spacing; the popular microATX size removes 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 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 (), 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.Scott Mueller, Upgrading and Repairing PCs, Eleventh Edition, Que Books, 1999, , page 1255
Form factor Originated Date Max. sizedepth × width Notes(typical usage, market adoption, etc.) ATX Intel 1995 12 × 9.6 in (305 × 244 mm) 7 Original, successor to AT motherboard 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. Intended for two CPU sockets. Extended ATX (commonly) 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 YTX Asus, MSI & Maxsun 2023 6.89 × 9.65 in (175 × 245 mm) 1 New form factor supporting the DIY-APE initiative
Although true E-ATX is most motherboard manufacturers also refer to motherboards with measurements , , and 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. The firm called the new design of this motherboard "Ultra ATX" 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.
The name "XL-ATX" has been used by at least three companies in different ways:
In September 2009, EVGA Corporation had already released a "XL-ATX" motherboard as its EVGA X58 Classified 4-Way SLI, which requires an Ultra-ATX sized case to support four "double-slot" graphics cards. Gigabyte Technology launched another XL-ATX motherboard, with model number GA-X58A-UD9 in 2010 measuring at , and GA-X79-UD7 in 2011 measuring at . In April 2010, Gigabyte announced its 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 . 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 .
Power supply