Motherboard A motherboard (sometimes alternatively known as the mainboard, system board, baseboard, planar board or logic board, or colloquially, a mobo) is the main printed circuit board (PCB) found in general purpose microcomputers and other expandable systems. Motherboard components Expansion slots (PCI Express, PCI, and AGP) 3-pin case fan connectors. Back pane connectors. Heat sink. 4-Pin (P4) power connector. CPU Socket. Northbridge Southbridge BIOS Chip Processor SMPS - Switched Mode Power Supply Hard Drive RAM - Random Access Memory ROM - Read Only Memory Cabinet DVD Writer