• AT Baby -AT
  • Mini -ATX
  • Micro -ATX
  • FlexATX
  • Mini - DTX
  • Mini -ITX
  • Nano-ITX
  • Pico -ITX

The ATX (Advanced Technology Extended ) is a standard for housing, power supplies, motherboards and expansion cards of microcomputers. The ATX form factor was introduced in 1996 by Intel as a successor to the to improve on previous AT form factor. Despite the attempt to enforce the BTX format as a standard, the actual ATX format and the smaller version of MicroATX ( uATX also ) still (as of November 2013) the dominant formats for PCs and desktop computers. Big Tower usually have the format E-ATX.

  • 2.1 Dimensions
  • 2.2 Pin Assignment
  • 2.3 voltage tolerances
  • 2.4 Power Supply Standards


The Board size

  • ATX: 305 mm × 244 mm (12 " × 9.6 " )
  • XL -ATX: 345 mm × 262 mm ( 13.5 "× 10.3 " )
  • ATX EXtended: 308 mm × 340 mm ( server board format)
  • Mini -ATX: 284 mm × 208 mm ( 11.2 "× 8.2 " )
  • Micro -ATX: 244 mm × 244 mm (9.6 "× 9.6 " )
  • Flex -ATX: 229 mm × 191 mm (9 " x 7.5 ")
  • Mini -ITX: 170 mm × 170 mm (6.7 "× 6.7 " )
  • Nano-ITX: 120 mm × 120 mm (4.7 "× 4.7 " )
  • Pico -ITX: 100 mm × 72 mm (4 " x 2.8" )
  • E- ATX form factor: 305 mm x 330 mm (12 " × 13")

These are, down to the ATX standard itself, ajar to ATX specifications. Server Boards for two processors use the larger E-ATX format.

The advantages of this standard

  • Integration of I / O ports on the motherboard itself
  • " 90 degree rotation " over previous formats, ie processor and memory banks are now located next to the bus slots instead of behind. Long cards collide thus not with coolers or fans.
  • Polarity-protected power connector for the motherboard.
  • The power supply is internal, via a control voltage on and off, thus no voltage- carrying cable must be pulled through the computer case.
  • It was originally planned that the fan of the power supply should also cool the equipped only with a passive heatsink processor.


  • Through the integration of I / O components on the motherboard is a fault in no exchange is possible (maybe helps here but a plug-in card replacement)
  • Standby power consumption when the computer is not switched off with the main switch directly on the power supply. However, this is not always present.

With even faster and thus initially warmer processors and graphics cards, the ATX form factor triggers thermal limits, so that was defined by Intel 2003/2004 as a successor to the BTX format that could not prevail until 2006 on the market. In October 2006, Intel introduced the production of BTX motherboards, since, as Intel, the Core 2 Duo in terms of waste heat was so good that he does not need BTX - would though definitely still remain about by high-end graphics cards theoretical advantages. However, this never found as a typical " hobbyist goods " in the BTX systems mainly completely sold widely disseminated and are therefore not adapted to the cooling concept.


The AT standard knew at the back of the system in practice only a keyboard connector. Other interfaces had to be individually housed in the housing. ATX allows motherboard manufacturers to arrange these ports in a rectangular area on the case back. How do they use the space, is left to the manufacturers (although most here a basic pattern followed ). To ensure that no holes remain in the housing rear wall, every motherboard an appropriate aperture (I / O Shield, also called " O panel " ) must be attached. Their size is 160 × 45 mm.

Today's traditional color scheme of the interface is shown in revision 2.2 of the ATX specification.

Power supply

While in the old AT format of the power button was right in the primary circuit of the power supply, it is plugged in to the motherboard and ATX only supplies a control voltage to the electronics ( so-called soft switch). This makes it possible, for example, that the computer turns off by software itself. However, this is only a " soft off " state, which means the motherboard is still supplied with a standby voltage that can be passed on expansion cards. This enables features such as Wake-on- LAN or Wake on modem, where the "off " computer itself back on when you over the LAN comes in a special " wake- package" ( Magic Packet ) or the modem receives a call. Also, time-controlled switching on the computer is possible. A disadvantage is the standby power consumption and the risk of damage from voltage spikes from the mains, even if the computer is not running.

To start an ATX PSU without connecting the motherboard, the (mostly) green PowerSupplyOn line to ground ( usually black ) must be connected. Please note, however, is that the power supply without a load attached ( such as a hard disk) should be turned on never, as it can be damaged. Not have even Many power supplies with no load on the 5 volt and 12 -volt branch.

The trend towards increasingly high -hungry processors and graphics cards overtaxed soon the current carrying capacity of the original 20-pin ATX connector. Therefore, first, the additional four-pin plug P4 was introduced by Intel, which supplies the shift control for the processor via two contacts to 12 V and ground, and thus relieves the main power connector. A similar reinforcement meets the extension of the current 20 - pin ATX connector 24 poles, ready with the one additional cable for 12 V, 5 V, 3.3 V and ground. Since also the graphics card more and more electricity consumed (nowadays consumes a high- end graphics card with no trouble a multiple of the processor ), 2.2 6 -pin PCI Express power connector was introduced in ATX, the graphics card provides additional power, in addition to the 75 W through the motherboard.

In some ATX 2.x power supplies of 24-pin connector can also be separated in a 20-pin connector and a 4-pin auxiliary connector - this additional plug must not be confused with the ATX12V P4 connector. It is therefore deviating coded in the plug shape and has a different mounting fuse.


ATX power supplies typically have dimensions of approximately 6 "× 3.5" × 5.5 "or 15 cm × 8.6 cm × 14 cm (width × height × depth). Power supplies are designed with great performance often deeper.

Pin assignment

The picture shows the ATX 2.2 connector with 24 contacts on the computer board. The four contacts on the right side are separated from the remaining 20 contacts and may be omitted for older motherboards. The geometry of the plug contacts ensures that the plug can only be inserted correctly. A plastic hook on the plug snaps into the rail on the socket and secures the plug mechanically. From the rail of view to pin 1 is left outside, rotated according to the plug depending on the viewing direction. Pin 16 ( at 1.0 ATX pin 14) controls the power supply. If it is grounded, the power supply switches on the principal stresses.

Voltage tolerances

The following limits must be respected both at idle and under load. In a grid voltage fault they should be met even under full load for at least another 17 ms, to bridge short disturbances can.

Power supply standards

  • The 24-pin connector from the ATX 2.2 power supply fits into the 20-pin connector of an ATX 1.x to 2.1 motherboards ( 2 × 2 protruding pins), provided that the placement of the mainboards in the connection area allows it. In some ATX 2.x power supplies of 24-pin connector can also be separated in a 20-pin connector and a 4-pin auxiliary connector. (This additional plug must not be confused with the ATX12V P4 connector).
  • The 20-pin ATX connector from 1.x to 2.1 power supplies also fits into the 24-pin connector of an ATX 2.x motherboards ( 2 × 2 -pin sockets are empty ). Some ATX 2.2 motherboards require an additional 20 - to -24 -pin adapter to be operated successfully with an ATX 1.x to 2.1 PSU can.
  • The ATX 2.3 specification differs only slightly from the previous version. The required efficiency is increased from 75 to 80%. The required switch-on current consumption of the 12-volt line processor is reduced, so that the system now also starts at a very low processor power consumption. The upper limit of 240 VA per line was deleted by a current of more than 20 A on the 12 V line is possible.