ATX
Because the baby AT form factor was never made a true standard, many companies have taken liberties with different dimensions and design. The ATX is a form factor developed by Intel that closely conforms to the baby AT size. It puts together some of the better ideas, engineering and design to make a standard that is cheaper to develop, allows for better component access, and in some ways is faster and more stable.

The ATX board measures approximately 9.5" X 12" and takes the baby AT board and turns it 90 degrees to put the long edge of the board along the back of the computer case, which provides maximum space for expansion slots and I/O ports.

The different I/O ports, USB connector and the PS/2 keyboard and mouse connectors are stacked or 'layered' and hardwired directly to the motherboard. The absence of a cable connector reduces radio interference as well as production costs. The ATX motherboard also defines the number and placement of mounting holes and uses a different power connection and a different (PS/2) power supply.

The ATX standard also provides for a smaller 'mini ATX' form factor which cuts the size of a board down to 8.2" X 11.2" and removes one row of mounting holes. These boards will fit in a regular ATX style case.