What is a Motherboard? - Definition, Function & Diagram

Definition

A motherboard is one of the most essential parts of a computer system. It holds together many of the crucial components of a computer, including the central processing unit (CPU), memory and connectors for input and output devices. The base of a motherboard consists of a very firm sheet of non-conductive material, typically some sort of rigid plastic. Thin layers of copper or aluminum foil, referred to as traces, are printed onto this sheet. These traces are very narrow and form the circuits between the various components. In addition to circuits, a motherboard contains a number of sockets and slots to connect the other components.

 

Parts of a Motherboard

If you were to open up your computer and take out the motherboard, you would probably get pretty confused about all the different parts. Depending on the make and model of your computer, it might look something like the picture below.

 

Photograph of a typical motherboard of a desktop computer

To understand how computers work you don't need to know every single part of the motherboard. However, it is good to know some of the most important parts and how the motherboard connects the various parts of a computer system together. Some of the typical parts are described below - they are also labeled in the next photograph:

• A CPU socket - the actual CPU is directly soldered onto this socket. Since high speed CPUs generate a lot of heat, there are heat sinks and mounting points for fans right next to the CPU socket.
• A power connector to distribute power to the CPU and other components.
• Slots for the system's main memory, typically in the form of DRAM chips.
• A chip forms an interface between the CPU, the main memory and other components. On many types of motherboards this is referred to as the Northbridge. This chip also contains a large heat sink.
• A second chip controls the input and output (I/O) functions. It is not connected directly to the CPU but to the Northbridge. This I/O controller is referred to as the Southbridge. The Northbridge and Southbridge combined are referred to as the chipset.
• Several connectors, which provide the physical interface between input and output devices and the motherboard. The Southbridge handles these connections.
• Slots for one or more hard drives to store files. The most common types of connections are Integrated Drive Electronics (IDE) and Serial Advanced Technology Attachment (SATA).
• A Read-only memory (ROM) chip, which contains the firmware, or startup instructions for the computer system. This is also called the BIOS.
• A slot for a video or graphics card. There are a number of different types of slots, including Accelerated Graphics Port (AGP) and Peripheral Component Interconnect Express (PCIe).
• Additional slots to connect hardware in the form of Peripheral Component Interconnect (PCI) slots. 

  Photograph of a typical motherboard with the most important parts labeled

There are certainly a lot of acronyms to get used to! Don't worry too much about trying to remember all the parts and their acronyms. The key is to remember that the motherboard contains the central processing unit, the memory, and all the connectors to the rest of the hardware of the computer system. The board is the 'mother' of all components - that's where it gets its name.

 

Schematic Diagram

Another useful way to look at the motherboard is as a schematic diagram. This is more of a logical organization of how the various parts are connected rather than where they are physically located on the sheet of plastic. The connections between these components are referred to as buses. So there is a CPU bus, a memory bus, etc.