What is a Motherboard?

The motherboard is a Printed Circuit Board (PCB), which holds the main part of a computer, the Processor (also called Central Processing Unit, or CPU). The motherboard includes all the necessary wiring for the processor to communicate with all other elements that make a computer: the memory (also called Random Access Memory, or RAM), the extension card slots (where you plug the video card, sound card, hard drive controller, SCSI card…), the drives (hard drive, floppy disk drive, CD-ROM, DVD...).

In other words, the motherboard is the essential part of a computer and all external components somehow plug into the motherboard. Since there is a limited number of motherboard manufacturers, their production is super massive and therefore motherboards are relatively cheap, ranging from US$100 for a plain Pentium board to US$400 for a top-of-the-line dual Pentium II board (that is without the processor itself, of course).

Motherboards come in different flavors and I am trying here to classify them by property.

Processor Type. The processor is the brain of the whole computer and is therefore the most important (and expensive) part. There are very few PC processor manufacturers, uncluding Intel (they make the Pentium, the Pentium Pro and the Pentium II), AMD (they make the K6) and Cyrix (they make the 6x86MX). Most of these processors now integrate the MMX technology (MultiMedia eXtention), which optimizes video and image operations (games, video editing, watching TV on your PC…). Motherboards are always design for one type of processor only.

Clock Speed. The clock speed is the heart beat of the system. It is measured in megahertz (MHz), and 1 MHz = 1 million heart beats per second. On a motherboard (and on a computer in general), there are 2 different, almost unrelated, clock speeds:

1. the bus clock speed, which is the speed at which the processor communicates with the memory, the video card, the sound card... The bus is managed by the PCI Chipset, which is detailed later. The bus clock speed is, on Pentium and PentiumII systems, 60Mhz, 66.66Mhz or since April 1998, 100MHz. For the little story, these numbers date from the first Pentium 60MHz and 66MHz processors of long time ago which were running at the same speed as the bus (60Mhz and 66.66Mhz) for a cool syncronization between the processor and all other components. Since it is much easier to improve the processor clock speed than the bus clock speed, we are stuck with buses up to 5 times slower than the processor.
   
   
2. the processor clock speed, which is the speed at which the processor operates internally. For instance a Pentium 200Mhz runs at 200Mhz, or 200 millions heart beats per second. Oh, I said that the processor clock speed and bus clock speed are almost unrelated because the only relation is that the processor clock speed is a multiplier of the bus speed: a Pentium 200 runs as 3 times the bus speed (3 times 66.66 = 200) and a Pentium II 300 runs as 5 times the bus speed (5 times 60 = 300).
   

Processor Speed. Processors run in different speed: 133Mhz, 150Mhz, 166Mhz, 180Mhz, 200Mhz, 233Mhx, 266Mhx, 300Mhz, 333Mhz, 350Mhz, and now 400Mhz... Motherboards are designed for one specific range of processor speed, for instance for Pentiums 133MHz-233Mhz, or Pentium IIs 233MHz-300MHz.

PCI Chipset. The PCI Chipset is the guy which controls communication (i.e. the bus) between the processor and the memory, the video card, the sound card, the hard drive controller… In other word, it is not because you have a faster processor than the guy next door that your sound or video is going to be faster (those are handled by the sound card or the video card). You should know that the PCI Chipset communicates with the RAM memory at its native speed (60MHz or 66.66MHz) but at only half that speed with the motherboard PCI slots (where you plug your video card, sound card, SCSI card…). There are very few PCI Chipset manufacturers, so you will often find the same ones on motherboards.

BIOS. The BIOS is the small software code (coded in a ROM chip mounted on the motherboard) which provides the computer with basic features such as reading from and writing to the RAM memory… There are very few BIOS manufacturers, so you will often find the same ones on motherboards.

RAM. The RAM (Random Access Memory) is the main memory of the system. It comes in different types (Fast Page, EDO, SDRAM...), different module sizes (4Mb, 8Mb, 16Mb, 32Mb, 64Mb...), different physical packages (72 pins or 168 pins packages) and of course from different manufacturers. Motherboards usually support several types and module sizes of RAM, but only one physical package type. RAM modules are mounted on the motherboard memory slots (motherboards include usually 4 or 8 slots, the higher the better). Fast Page RAM is the original RAM, EDO is the faster version and SDRAM is the RAM of the future because its 10 nanosecond access time makes it the only memory that will keep up with faster PCI clock speeds of 100MHz.

Extras. Some motherboards include other components, such as an USB (Universal Serial Bus), a VRM (Voltage Regulator Module), an AGP (Accelerated Graphics Port) processor overheating alarm… Some motherboards also include a video chip, a SCSI controller chip, a sound chip… but these chips are usually of just average quality and performance (convenient but average quality).

Board Size. There are two standard sizes for motherboards: Baby AT and ATX. Baby AT doesn't mean much as it doesn't refer to specific measurements. ATX on the other hand is a standard. ATX motherboards have the keyboard port, mouse port, 1 parallel port, 2 serial ports right on the board (no need to add a card for each unlike Baby AT boards), and ATX boards require a lot less cables than Baby AT boards. But ATX boards require an ATX case and an ATX power supply.