OK, the CMOS(Complementary Metal-Oxide Semiconductor) is a device that hosts the BIOS( Basic in out system). The BIOS holds all of the motherboard and chipset information. The BIOS is stored, and can be updated, in the CMOS. When you here someone say" I had to clear the CMOS to get the board to boot", it means they shorted a jumper and put all of the bios setings back to default. Tweaking the bios settings is what makes a board either fly, or crash

Resinboy