inside your computer
into which just about everything
plugs. Mainboards come in different types for different CPU
s and are now able to house either DDR RAM
Some boards are able to accomodate two (or more) CPUs. This is mainly for server computers and high-end workstations.
There are two main form factors available. The older style AT mainboard, which began to disappear with the emergence of the Pentium II boards, and the newer style ATX form factor for the modern computers.
Some mainboards have sound or video built into the PCB. These are usually used by system integrators to make cheap computers for tightass companies that complain when their users see a Blue Screen Of Death every second day.