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What is a Motherboard? - Definition, Function & Diagram

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Taught by

Paul Zandbergen

Paul has a PhD from the University of British Columbia and has taught Geographic Information Systems, statistics and computer programming for 15 years.

The motherboard is a sheet of plastic that holds all the circuitry to connect the various components of a computer system. Learn how the motherboard functions to make all the other components work together.

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
computer mother board

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
computer motherboard with labels

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.

Schematic diagram of a typical motherboard
schematic diagram of motherboard

The schematic diagram reflects how computer engineers think about a motherboard. Once they have determined the best design, then they have to figure out how to best get all the parts and their connections onto a small board. They have to consider size, heat, distances, circuitry, cables, etc. That's why it can be hard to see how the diagram and the photograph of the motherboard relate to reach other.

Technology development

One thing to remember about motherboards is that they continue to change very quickly. If you had a computer in the early 2000's, you may remember that the plugs for your mouse and keyboard looked very different than they do today. All of the components of a motherboard have seen significant changes over the years as technology continues to evolve. The basic function of a motherboard, however, has remained the same.

Have a look at the motherboard of a smart phone in the photograph below. Yes, a phone has a motherboard too - it contains a processing unit, memory and connectors to other parts.

Photograph of a motherboard of a smart phone
motherboard of a smartphone

You will notice that the motherboard is much smaller than those found in a desktop or laptop computer. Although it is a little harder to see, there are also fewer connectors. Many parts have become small enough they can fit on the motherboard without a separate connector. In the example of a smart phone most of the parts are in fact mounted directly onto the motherboard itself. This is partly why a modern smart phone is a more powerful computing device than a desktop computer from 15 years ago.

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