What is the Function of the Computer Motherboard?

The motherboard connects and controls all of the essential elements of a computer or digital device. The keyboard, the CPU, the video card, memory and the hard disk drive communicate with each other through the motherboard. Firmware on the motherboard controls and coordinates all basic functions.

Computer technician working
A technician holds a computer motherboard.
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Basic Input/Output Software

The motherboard contains basic input/output system code, or BIOS, in a read-only memory chip. BIOS code is firmware. Firmware code is not lost when power is turned off, and it cannot be altered by any normal operating system process or application software. The BIOS checks vital components on the motherboard at startup, and then, working with the CPU, loads the operating system into RAM.


The CPU, or microprocessor, is held in a socket on the motherboard. The socket allows the CPU to be replaced or upgraded, and dictates what kind of microprocessor can be used.

Microprocessors are made by a variety of manufacturers and have a wide range of capabilities and price tags. While you can upgrade a computer by putting a better microprocessor in the socket, the motherboard architecture will dictate exactly how far such an upgrade can go.

The Buses

A bus is a communication path on the motherboard that links major components together. The motherboard has a number of buses, including an address bus, a data bus, and an instruction bus. The style of motherboard is defined by the number of data bits that can be transferred simultaneously across the bus. A 32-bit data bus is found on 32-bit motherboards, for example, and a 64-bit motherboard will have a 64-bit bus.

The width of the data bus also determines the CPU and RAM your motherboard requires, as well as the operating system.

RAM and Storage Devices

RAM fits into sockets on the motherboard and provides the memory space to hold your operating system and application software while your computer is running. If your motherboard has empty RAM sockets, you can upgrade to add more RAM until all sockets are filled. The type of RAM you need depends upon your motherboard architecture (32-bit or 64-bit).

Storage devices hold your operating system, application software and data while the computer is turned off. The hard disk drive and DVD drive are examples of storage devices. Most motherboards are capable of connecting to multiple devices through internal ports, or connectors.


Ports connect hardware to the motherboard. Devices like the keyboard, the mouse, speakers, microphones, USB devices, and local area networks connect to external ports that you can reach without removing the computer cabinet. Hard disk drives, DVD drives, CPU cooling system fans and other internal devices connect to internal ports.

Expansion Slots

Expansion slots are usually found on motherboards in desktop PCs, and the number and type of slots available depend on the manufacturers. Circuit boards plug into expansion slots and add functions to the computer. There are a variety of different styles of expansion slots, and the card must match the slot or you may damage it or the motherboard if you try to insert it.

Laptops, notebooks, and tablets may have no expansion slots, or they may have proprietary expansion ports that serves the same purpose. Check your owner's manual for information about the expansion slots on the motherboard in your computer.