How Motherboards Work

By: Tracy V. Wilson & Chris Pollette  | 
computer motherboard
The motherboard allows all the components in your computer to "talk" to each other. Andrew Brookes/Getty Images

If you've ever taken a computer apart, you've seen the one piece of equipment that ties everything together — the motherboard. A motherboard is the central circuit board that has the components and connectors that allow all the parts of your computer to receive power and communicate with one another. It is sometimes referred to as the mainboard, main circuit board or base board. Motherboards typically boast a wide variety of built-in features, and they directly affect a computer's capabilities and potential for upgrades.

Motherboards are certainly not a new invention. They could be found in mainframe computers before the personal computer revolution. The first PC motherboards held very few actual components. The first IBM PC motherboard had only a processor and card slots. Users plugged components like floppy drive controllers and memory into the slots. Compaq was the first to use a motherboard not derived from an IBM design. This new design used a processor from Intel. Although some in the industry thought it was a gamble, when Compaq's sales took off, other companies followed suit.

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By the 1990s, Intel controlled around 40 percent of the PC's motherboard market. Today, the biggest players are Asus, Gigabyte Technology and Micro-Star International (MSI). Asus, the largest motherboard manufacturer in the world, controls around 13 percent of the market. Intel is still in the top 10 of motherboard manufacturers.

In this article, we'll look at the general components of a motherboard. Then, we'll closely examine five points that dramatically affect what a computer can do.

Form Factor

modern motherboard
A diagram of a modern motherboard. Outline2Design/HowStuffWorks

The motherboard's main job is to hold the computer's microprocessor chip and enable other parts of the computer to connect to it. Everything that runs the computer or enhances its performance is either part of the motherboard or plugs into it via a slot or port.

The shape and layout of a motherboard is called its form factor. The form factor affects where individual components go and the shape of the computer's case. There are several specific form factors that most PC motherboards use so that they can all fit in standard cases.

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The form factor is just one of the many standards that apply to motherboards. Here are some of the other standards:

  • The socket for the microprocessor determines what kind of central processing unit (CPU) the motherboard can use.
  • The chipset is part of the motherboard's logic system and is usually made of two parts — the northbridge and the southbridge. These two "bridges" connect the CPU to other parts of the computer.
  • The basic input/output system (BIOS) controls the most basic functions of the computer and performs a self-test every time you turn it on. Some systems feature dual BIOS, which provides a backup in case one fails or in case of error during updating.
  • The real time clock chip is a battery-operated chip that maintains basic settings and the system time.

The slots and ports found on motherboards include:

Form factor is one of many standards that apply to motherboards.
Form factor is one of many standards that apply to motherboards.
Photo courtesy of Consumer Guide Products

Some motherboards incorporate newer technological advances:

  • Redundant Array of Independent Discs (RAID) controllers allow the computer to recognize multiple drives as one drive.
  • PCI Express is a newer protocol that acts more like a network than a bus (circuit that connects one part of the motherboard to another). It can eliminate the need for other ports, including the AGP port.
  • Rather than relying on plug-in cards, some motherboards have on-board sound, networking, video or other peripheral support.

Many people think of the CPU as one of the most important parts of a computer. We'll look at how it affects the rest of the computer in the next section.

Sockets and CPUs

motherboard with CPU sockets
A computer mainboard or motherboard with blue CPU sockets. stockphoto-graf/Shutterstock

The CPU is the first thing that comes to mind when many people think about a computer's speed and performance. The faster the processor, the faster the computer can operate. Manufacturers use standard sets of pins to connect the CPU to the motherboard, called the Pin Grid Array (PGA). The different pin-and-socket layouts result from further research and development and are designed to make the most of the processor's capabilities.

CPU manufacturers have used a variety of PGAs. Motherboard socket arrangements are often named for the number of pins in the PGA. Architectures change quite often, but some examples include:

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  • Socket 7 — for mid-1990s Intel processors, although competitors also adopted this architecture
  • Socket 478 — for older Pentium and Celeron processors
  • Socket 754 — for AMD Sempron and some AMD Athlon processors
  • Socket 939 — for newer and faster AMD Athlon processors

Newer Intel CPUs use an LGA, which stands for Land Grid Array. An LGA is different from a PGA in that the pins are part of the socket, not the CPU. LGAs also come in specific configurations, such as:

  • LGA 1200 — for Intel's 10th generation processors, released in 2020
  • LGA 3647 — for Xeon and Skylake processors
  • LGA 775, aka Socket T — a classic Intel layout used with the Pentium 4 and some later generations

Anyone building a PC with a specific CPU in mind should select a motherboard based on that CPU. For example, if you want to use one of the newest multi-core chips made by Intel or AMD, you will need to select a motherboard with the correct socket for those chips.

The CPU communicates with other elements of the motherboard through a chipset. We'll look at the chipset in more detail next.

Chipsets

The chipset is the "glue" that connects the microprocessor to the rest of the motherboard and therefore to the rest of the computer. On older PCs, it consists of two basic parts — the northbridge and the southbridge. All of the various components of the computer communicate with the CPU through the chipset.

The northbridge connects directly to the processor via the front side bus (FSB). A memory controller located on the northbridge gives the CPU fast access to the memory. The northbridge also connects to the AGP or PCI Express bus and to the memory itself.

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The southbridge is slower than the northbridge, and information from the CPU must go through the northbridge before reaching the southbridge. Other buses connect the southbridge to the PCI bus, the USB ports and the IDE or SATA hard disk connections.

In the early 2000s, Intel processors began using the Intel Hub Architecture, or IHA. It may also be referred to as the Accelerated Hub Architecture (AHA). The newer architecture uses its own buses, in the process dropping PCI entirely. IHA chips do not have a northbridge or southbridge. Instead, they have a Graphics and AGP Memory Controller Hub, or GMCH, and an I/O (input/output) Controller Hub, or ICH.

The GMCH performs a similar role to the northbridge, working with memory and graphics. The ICH takes over the jobs of the southbridge.

Chipset selection and CPU selection go hand in hand because manufacturers optimize chipsets to work with specific CPUs. The chipset is an integrated part of the motherboard, so it cannot be removed or upgraded. This means that not only must the motherboard's socket fit the CPU, the motherboard's chipset must work optimally with the CPU.

Next, we'll look at buses, which, like the chipset, carry information from place to place.

Bus Speed

Busses connect different parts of the motherboard to one another.
Busses connect different parts of the motherboard to one another.
HowStuffWorks

A bus is a circuit that connects one part of the motherboard to another. The more data it can handle at one time, the faster it allows information to travel. The speed of the bus refers to how much data can move across the bus simultaneously.

In newer motherboards using PCIe, you might see bandwidth described in terms of numbers of lanes, which function like lanes on a street. Each lane has two pairs of wires, one for receiving information and the other to transmit. Unlike what you see on city streets however, the lanes are inside the bus. Each device needs enough lanes to manage the throughput it needs. If you're building a high-end gaming machine with a powerful graphics card, you'll want more lanes, but for a simple daily work computer you probably don't need as many.

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Bus speed usually refers to the speed of the front side bus (FSB), which connects the CPU to the northbridge. FSB speeds can range from 66 MHz to over 800 MHz. Since the CPU reaches the memory controller though the northbridge, FSB speed can dramatically affect a computer's performance.

Here are some of the other busses found on a motherboard:

  • The back side bus connects the CPU with the level 2 (L2) cache, also known as secondary or external cache. The processor determines the speed of the back side bus.
  • The memory bus connects the northbridge to the memory.
  • The IDE or ATA bus connects the southbridge to the disk drives.
  • The AGP bus connects the video card to the memory and the CPU. The speed of the AGP bus is usually 66 MHz.
  • The PCI bus connects PCI slots to the southbridge. On most systems, the speed of the PCI bus is 33 MHz. Also compatible with PCI is PCI Express, which is much faster than PCI but is still compatible with current software and operating systems. PCI Express is likely to replace both PCI and AGP buses.

The faster a computer's bus speed, the faster it will operate — to a point. A fast bus speed cannot make up for a slow processor or chipset.

Now let's look at memory and how it affects the motherboard's speed.

Memory and Other Features

DDR DIMM RAM
A closeup of a DDR DIMM RAM memory module. nikkytok/Shutterstock

We've established that the speed of the processor itself controls how quickly a computer works. The speed of the chipset and buses controls how quickly it can communicate with other parts of the computer. The speed of the RAM connection directly controls how fast the computer can access instructions and data, and therefore has a big effect on system performance. A fast processor with slow RAM is going nowhere.

The amount of memory available also controls how much data the computer can have readily available. RAM makes up the bulk of a computer's memory. The general rule of thumb is the more RAM the computer has, the better.

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Much of the memory available today is dual data rate (DDR) memory. This means that the memory can transmit data twice per cycle instead of once, which makes the memory faster. Also, most motherboards have space for multiple memory chips, and on newer motherboards, they often connect to the northbridge via a dual bus instead of a single bus. This further reduces the amount of time it takes for the processor to get information from the memory.

In the earliest days of motherboards, virtually everything other than the processor came on a card that plugged into the board. Now, motherboards feature a variety of onboard accessories such as LAN support, video, sound support and RAID controllers.

Motherboards with all the bells and whistles are convenient and simple to install. There are motherboards that have everything you need to create a complete computer — all you do is plug the motherboard in a case and add a hard disk and a power supply. You have a completely operational computer on a single board.

For many average users, these built-in features provide ample support for video and sound. For avid gamers and people who do high-intensity graphic or computer-aided design (CAD) work, however, separate video cards provide much better performance.

Originally Published: Jul 20, 2005

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