ATX Motherboard Specification

Release 2.01 of the ATX Specification (February 1997) makes minor adjustments to Release 2.0, which incorporated a number of new features, additional requirements, and clarifications. These changes take into account support for the next generation of ATX motherboards, while maintaining compatibility with the first generation. Readers should examine their combination of motherboard, power supply and chassis needs to determine whether they require the additional features found in Release 2.01

The ATX specification has been written as a specification for the PC industry, designed to add value to the PC. It defines a new PC form-factor that will allow PC manufacturers to build products more cheaply, improve ease of use and serviceability, and incorporate new and exciting I/O features with ease. The ATX form factor is essentially a Baby-AT baseboard rotated 90 degrees within the chassis enclosure and a new mounting configuration for the power supply. In this way, the processor is relocated away from the expansion slots, allowing them all to hold full length add-in cards. ATX defines a double height aperture to the rear of the chassis which can be used to host a wide range of on-board I/O. Only the size and position of this aperture is defined, allowing PC manufacturers to add new I/O features (e.g.; TV input, TV output, joystick, modem, LAN, audio, etc.) to systems that will help them differentiate their products in the marketplace, and better meet the needs of end users.

A change to the system form-factor is ultimately of little benefit if it doesn't reduce overall system cost. ATX achieves this in a number of ways.

• By integrating more I/O down onto the board and better positioning the hard drive and floppy connectors material cost of cables and add-in cards is reduced.
• By reducing the number of cables and components in the system, manufacturing time and inventory holding costs are reduced and reliability will increase.
• By using an optimized power supply, it's possible to reduce cooling costs and lower acoustical noise. An ATX power supply, which has a side-mounted fan, allows direct cooling of the processor and add-in cards making a secondary fan or active heatsink unnecessary in most system applications.

ATX is a specification that is freely available to the whole industry. The current revision (2.0) incorporates feedback from the many chassis and power supply vendors making ATX products.

The specification is available for download in Adobe Acrobat format (357 KB).

More information about the ATX specification and vendors is available at http://www.teleport.com/~atx.

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