ATX
ATX
(hardware, standard)ATX is a development of the Baby AT specification with themotherboard rotated 90 degrees in the chassis. The CPU andSIMM sockets have been relocated away from the expansion card slots meaning that all the slots support full-lengthcards. More I/O functions are integrated on themotherboard. As the longer edge of the board is now at theback of the chassis, there is more space for connectors; also,the I/O opening on the back panel of the chassis has beendefined as double the previous height, allowing vendors to addextra on-board I/O functions over and above the standard.
Most Pentium Pro boards use this form factor.
As well as the motherboard size, layout, and placement, theATX specification also includes requirements for power supplyand fan specification and location.
The full size ATX board measures 305mm wide by 244mm deep.There is also a Mini-ATX form factor, 284mm by 208mm.
http://developer.intel.com/design/motherbd/atx.htm.