A motherboard is the main printed circuit board (PCB) in a computer. The motherboard is a computer’s central communications backbone connectivity point, through which all components and external peripherals connect.
The large PCB of a motherboard may include 6-14 layers of fiberglass, copper connecting traces and copper planes for power and signal isolation. Additional components can be added to a motherboard through its expansion slots. These may include processor sockets, DIMM, HTX, PCI, PCIe and M.2 slots as well as power supply connections. Typically motherboards offer additional connectivity through a Southbridge chip such as PCI, SATA, Thunderbolt, USB and more. CPU to RAM and PCIe are generally connected through point-to-point interconnects such as hypertransport (HT), quick path interconnect (QPI) or Ultrapath interconnect (UPI). Often, choosing a motherboard determines many of the features a desktop will have.
The most common motherboard design in desktop computers today is ATX, an Intel improvement on the AT design by IBM. Other form factors include extended ATX mini-ATX, microATX, BTX, microBTX mini ITX, micro ITX and nano ITX.
The integration of components has eliminated the Northbridge chips that managed memory from motherboards. With the advent of memory controllers built into CPU, integrated video too has moved from motherboard to CPU. On AMD’s new Ryzen, even the Southbridge is optional due to the SOC (system on a chip) nature of the CPU. This integration into the CPU reduces the cost for motherboard manufacturers who wish to offer base systems for workstations and entry level computers while also enabling highly customized implementations that support a range of processors to allow for platform upgradabillity.