The modern-day shape and layout of PC motherboards. It improves on the previous standard, the Baby AT form factor, by rotating the orientation of the board 90 degrees. This allows for a more efficient design, with disk drive cable connectors nearer to the drive bays and the CPU closer to the power supplyand cooling fan.
Also see From AT to BTX: Motherboard Form Factors in Webopedia’s “Did You Know…?” section.
