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How Motherboards Workby Tracy V. Wilson and Ryan Johnson

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Introduction to How Motherboards Work

If you've ever taken the case off of a computer, you've seen the one piece of equipment that ties everything together --the motherboard. A motherboard allows all the parts of your computer to receive power and communicate with oneanother.

Motherboards have come a long way in the last twenty years. The first motherboards held very few actual components.The first IBM PC motherboard had only a processor and card slots. Users plugged components like floppy drivecontrollers and memory into the slots.

Today, motherboards typically boast a wide variety of built-in features, and theydirectly affect a computer's capabilities and potential for upgrades.

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

Form Factor

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Photo courtesy Consumer Guide ProductsA modern motherboard.

Photo courtesy Consumer Guide ProductsA Socket 754 motherboard

Photo courtesy HowStuffWorks ShopperA Socket 939 motherboard

A motherboard by itself is useless, but a computer has to have one to operate. Themotherboard's main job is to hold the computer's microprocessor chip and leteverything else connect to it. Everything that runs the computer or enhances itsperformance is either part of the motherboard or plugs into it via a slot or port.

The shape and layout of a motherboard is called the form factor. The form factoraffects where individual components go and the shape of the computer's case. Thereare several specific form factors that most PC motherboards use so that they can allfit in standard cases. For a comparison of form factors, past and present, check outMotherboards.org.

The form factor is just one of the many standards that apply to motherboards. Someof the other standards include:

The socket for the microprocessor determines what kind of CentralProcessing Unit (CPU) the motherboard uses.The chipset is part of the motherboard's logic system and is usually made oftwo parts -- the northbridge and the southbridge. These two "bridges" connectthe CPU to other parts of the computer.The Basic Input/Output System (BIOS) chip controls the most basic functions ofthe computer and performs a self-test every time you turn it on. Some systemsfeature 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 a motherboard include:

Peripheral Component Interconnect (PCI)- connections for video, sound and video capture cards, as well as network cardsAccelerated Graphics Port (AGP) - dedicated port for video cards.Integrated Drive Electronics (IDE) - interfaces for the hard drivesUniversal Serial Bus or FireWire - external peripheralsMemory slots

Some motherboards also incorporate newer technological advances:

Redundant Array of Independent Discs (RAID) controllers allow the computerto recognize multiple drives as one drive.PCI Express is a newer protocol that acts more like a network than a bus. Itcan eliminate the need for other ports, including the AGP port.Rather than relying on plug-in cards, some motherboards have on-boardsound, networking, video or other peripheral support.

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

Sockets and CPUs

The CPU is thefirst thing thatcomes to mindwhen manypeople thinkabout acomputer'sspeed andperformance.The faster theprocessor, thefaster thecomputer canthink. In theearly days ofPC computers,all processorshad the sameset of pins thatwould connectthe CPU to the motherboard, called the Pin Grid Array (PGA). These pins fit into a socket layout called Socket 7. This meant that any processor would fitinto any motherboard.

Today, however, CPU manufacturers Intel and AMD use a variety of PGAs, none of which fit into Socket 7. As microprocessors advance, they need moreand more pins, both to handle new features and to provide more and more power to the chip.

Current socket arrangements are often named for the number of pins in the PGA. Commonly used sockets are:

Socket 478 - for older Pentium and Celeron processorsSocket 754 - for AMD Sempron and some AMD Athlon processorsSocket 939 - for newer and faster AMD Athlon processorsSocket AM2 - for the newest AMD Athlon processorsSocket A - for older AMD Athlon processors

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Photo courtesy HowStuffWorks ShopperA Socket LGA755 motherboard

Photo courtesy HowStuffWorks ShopperThe northbridge and southbridge

Busses connect different parts of the motherboard to oneanother

RAM Memory

For information about different types of RAM,

The newest Intel CPU does not have a PGA. It has an LGA, also known as Socket T.LGA stands for Land Grid Array. An LGA is different from a PGA in that the pins areactually part of the socket, not the CPU.

Anyone who already has a specific CPU in mind should select a motherboard basedon that CPU. For example, if you want to use one of the new multi-core chips made byIntel or AMD, you will need to select a motherboard with the correct socket for thosechips. CPUs simply will not fit into sockets that don't match their PGA.

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 isthe "glue" thatconnects themicroprocessorto the rest ofthe motherboardand therefore tothe rest of thecomputer. On aPC, it consistsof two basicparts -- thenorthbridgeand thesouthbridge.All of the variouscomponents ofthe computercommunicatewith the CPUthrough the chipset.

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

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

Chipset selection and CPU selection go hand in hand, because manufacturers optimize chipsets to work with specific CPUs. The chipset is an integrated partof 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 chipsetmust work optimally with the CPU.

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

Bus Speed

A bus is simply a circuit that connects one part of the motherboard to another. Themore data a bus can handle at one time, the faster it allows information to travel. Thespeed of the bus, measured in megahertz (MHz), refers to how much data can moveacross the bus simultaneously.

Bus speed usually refers to the speed of the front side bus (FSB), which connectsthe 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 candramatically 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 knownas secondary or external cache. The processor determines the speed of theback 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 speedof the AGP bus is usually 66 MHz.The PCI bus connects PCI slots to the southbridge. On most systems, thespeed 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 andoperating systems. PCI Express is likely to replace both PCI and AGP busses.

The faster a computer's bus speed, the faster it will operate -- to a point. A fast busspeed 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

We've established that the speed of the processor itself controls how quickly a computer thinks. Thespeed of the chipset and busses controls how quickly it can communicate with other parts of thecomputer. The speed of the RAM connection directly controls how fast the computer can accessinstructions and data, and therefore has a big effect on system performance. A fast processor with

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check out How RAM Works.

Photo courtesy HowStuffWorks Shopper64MB SDRAM SIMM

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.

Photo courtesy HowStuffWorks Shopper184-pin DDR DIMM RAM

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 thenorthbridge 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.

Photo courtesy HowStuffWorks Shopper200-pin DDR SODIMM RAM

A motherboard's memory slots directly affect what kind and how much memory is supported. Just like other components, the memory plugs into the slot viaa series of pins. The memory module must have the right number of pins to fit into the slot on the motherboard.

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

Motherboards with all the bells and whistles are convenient and simple to install. There are motherboards that haveeverything you need to create a complete computer -- all you do is stick the motherboard in a case and add a hard disk,a CD drive 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 peoplewho do high-intensity graphic or computer-aided design (CAD) work, however, separate video cards provide much betterperformance.

For more information on motherboards and related topics, check out the links on the following page.

Lots More Information

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Basic Computer Operation TutorialHow Motherboards Are MadeThe History of the ComputerComputer History MuseumMemory Architectures

Sources

Basic Computer Operation Tutorialhttp://www.bcae1.com/comptutorial/computertutorial.htmHow Motherboards Are Made: A Gigabyte Factory Tourhttp://www.pcstats.com/articleview.cfm?articleid=1722&page=3Installing Motherboardshttp://www.pcmech.com/show/motherboards/85/Motherboard Basicshttp://www.pcmech.com/show/motherboards/119/Motherboard Definitionhttp://www.sceptre.com/Products/Motherboard/definitions/definitions_board.htmPCGuide - http://www.pcguide.com/ref/mbsys/index.htmPCGuide - http://www.pcguide.com/ref/mbsys/buses/types/pci.htmThe PC Technology Guide: Motherboardshttp://www.pctechguide.com/01mboards.htmPCWorld.com - How to Buy a Motherboardhttp://www.pcworld.com/howto/bguide/0,guid,29,00.aspUpgrading & Repairing PCs Eighth Editionhttp://cma.zdnet.com/book/upgraderepair/ch04/ch04.htmPCWorld.com - How to Buy a Motherboardhttp://www.pcworld.com/howto/bguide/0,guid,29,page,1,00.aspPCWorld.com - Your Ideal PChttp://www.pcworld.com/howto/article/0,aid,116993,pg,3,00.aspPCWorld.com - Up Front: Want a PC Done Right? Do It Yourself!http://www.pcworld.com/howto/article/0,aid,119974,00.aspUnderstanding System Memory and CPU Speedshttp://www.directron.com/fsbguide.htmlPC World | Motherboards Buying Guidehttp://www.pcworld.idg.com.au/index.php/id;641784313Motherboardshttp://www.pcmech.pair.com/mbindex.htmTriumph of the Nerds: A History of the Computerhttp://www.pbs.org/nerds/timeline/index.htmlThe Old Computer Hut - Intel family microcomputershttp://www.arcula.demon.co.uk/intl1.htmPersonal Computer Motherboards, Comparedhttp://is.lse.ac.uk/History/Motherboards.htmPC Guide: The Memory Bushttp://www.pcguide.com/ref/ram/timingBus-c.htmlMotherboards.org: Understanding PCI Expresshttp://www.motherboards.org/articles/tech-planations/1438_1.htmlMotherboards.org: Expansion Slots Rev 1.3http://www.motherboards.org/articles/tech-planations/920_1.htmlMotherboards.org: Motherboard Basics Rev 1.1http://www.motherboards.org/articles/tech-planations/1_1.htmlArs Technica: PCI Express: An Overviewhttp://arstechnica.com/articles/paedia/hardware/pcie.ars/1ATA (IDE) Bushttp://www.interfacebus.com/Design_Connector_IDE.html

Related HowStuffWorks Articles

How BIOS WorksHow Caching WorksHow RAM WorksHow Microprocessors WorkHow Computer Memory WorksHow Microcontrollers WorkHow AGP WorksHow IDE Controllers WorkHow PCI WorksHow SCSI WorksHow USB Ports WorkHow Sound Cards WorkHow PCs Work

More Great Links

Basic Computer Operation TutorialHow Motherboards Are MadeThe PC Technology GuideTom's Hardware Guide

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Web Pages

Basic Computer Operation Tutorialhttp://www.bcae1.com/comptutorial/computertutorial.htmHow Motherboards Are Made: A Gigabyte Factory Tourhttp://www.pcstats.com/articleview.cfm?articleid=1722&page=3Installing Motherboardshttp://www.pcmech.com/show/motherboards/85/Motherboard Basicshttp://www.pcmech.com/show/motherboards/119/Motherboard Definitionhttp://www.sceptre.com/Products/Motherboard/definitions/definitions_board.htmPCGuide - http://www.pcguide.com/ref/mbsys/index.htmPCGuide - http://www.pcguide.com/ref/mbsys/buses/types/pci.htmThe PC Technology Guide: Motherboardshttp://www.pctechguide.com/01mboards.htmPCWorld.com - How to Buy a Motherboardhttp://www.pcworld.com/howto/bguide/0,guid,29,00.aspUpgrading & Repairing PCs Eighth Editionhttp://cma.zdnet.com/book/upgraderepair/ch04/ch04.htmPCWorld.com - How to Buy a Motherboardhttp://www.pcworld.com/howto/bguide/0,guid,29,page,1,00.aspPCWorld.com - Your Ideal PChttp://www.pcworld.com/howto/article/0,aid,116993,pg,3,00.aspPCWorld.com - Up Front: Want a PC Done Right? Do It Yourself!http://www.pcworld.com/howto/article/0,aid,119974,00.aspUnderstanding System Memory and CPU Speedshttp://www.directron.com/fsbguide.htmlPC World | Motherboards Buying Guidehttp://www.pcworld.idg.com.au/index.php/id;641784313Motherboardshttp://www.pcmech.pair.com/mbindex.htmTriumph of the Nerds: A History of the Computerhttp://www.pbs.org/nerds/timeline/index.htmlThe Old Computer Hut - Intel family microcomputershttp://www.arcula.demon.co.uk/intl1.htmPersonal Computer Motherboards, Comparedhttp://is.lse.ac.uk/History/Motherboards.htmPC Guide: The Memory Bushttp://www.pcguide.com/ref/ram/timingBus-c.htmlMotherboards.org: Understanding PCI Expresshttp://www.motherboards.org/articles/tech-planations/1438_1.htmlMotherboards.org: Expansion Slots Rev 1.3http://www.motherboards.org/articles/tech-planations/920_1.htmlMotherboards.org: Motherboard Basics Rev 1.1http://www.motherboards.org/articles/tech-planations/1_1.htmlArs Technica: PCI Express: An Overviewhttp://arstechnica.com/articles/paedia/hardware/pcie.ars/1ATA (IDE) Bushttp://www.interfacebus.com/Design_Connector_IDE.html

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