ARCHIVED: What is the ATX form factor?

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Form factor refers to the physical size and shape (according to outside dimensions) of a computer device. It is most often used to describe the size of circuit boards, especially the motherboard and expansion cards.

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ATX form factor

The ATX form factor is a replacement for the older AT and baby AT form factors. Invented by Intel in 1995, it incorporates the first major change in the layout of PC motherboards to occur in years. The ATX motherboard rotates the orientation of the board 90 degrees. This allows for a more efficient design, with disk drive cable connectors closer to the drive bays and the CPU closer to the power supply and cooling fan. All Intel motherboards currently produced are ATX motherboards. Generally speaking, an ATX motherboard is required to use the newest Intel processors. Because of this and the general improvements that ATX brings, the ATX form factor is the form factor of choice for both commercial mass-production systems and for home PC builders.

The ATX form factor involves changes not only to the motherboard design and layout, but also to the case and power supply as well. Improvements and changes are listed below:

  • Integrated I/O port connectors
  • Integrated PS/2 mouse connector
  • Reduced drive bay interference
  • Reduced expansion card interference
  • Better power supply connector
  • "Soft Power" support
  • 3.3V power support
  • Better air flow
  • Improved upgradability

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ATX motherboard and case design

The ATX case looks very similar to the baby AT case, except that the holes in back for ports and keyboard and mouse connectors have been altered to allow for the different design of the ATX motherboard. In particular, the ATX motherboard has integrated I/O ports mounted directly on the edge of the board. Most ATX motherboards have, from left to right, stacked keyboard and mouse ports, stacked USB ports, printer and game ports along the top, and two serial ports along the bottom. This design can differ based on the manufacturer of the motherboard. This allows for a much more effective use of interior case space, and decreases the number of cables and connectors that can become disconnected or damaged.

ATX cases often have more drive bays for a given case size. For example, a mid-tower ATX case will often have more available drive bays than a baby AT case of the same size. The ATX case design also generally provides easier interior access to expansion bays.

The ATX power supply is different in a number of important ways. ATX power supplies and motherboards function at 3.3 volts or lower, instead of 5 volts, reducing motherboard cost, energy consumption, and heat production. The fan on the power supply is reversed so that it blows air into rather than out of the case, which helps keep the case clean and reduces heat buildup. This is necessary due to the high heat produced by the new generation of Intel Pentium II/III and AMD processors. The ATX power supply is turned on and off using electronic signaling instead of a physical toggle switch. This allows the computer to be turned on and off using software control, thus improving power management and energy-saving features. Because of this, ATX power supplies must be matched with ATX motherboards.

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Last modified on 2018-01-18 12:31:19.