Building your own computer
There are well over a dozen motherboard manufacturers. Firstly, the motherboards must be for the correct processor. If you are using an Intel processor (eg Pentium) then the motherboards will be made especially for that processor. The same applies to processors made by AMD for their range of processors (eg Athlon).
The motherboards will therefore be known by the type of processor socket built onto the motherboard. For Athlons it is currently known as Socket A. For Intel Pentium IV it is Socket 478 (which actually refers to the number of pins on the processor. Good job we don't name our cars in the same way). For Pentium III, Celeron and Cyrix processors it is Socket 370.
Not all motherboards can accommodate the entire range of a particular manufacturers processors, although this mainly refers to newer, faster processors. For example, your choice of Whiz-Bang motherboard at the time of purchase could, s ay, run AMD Athlons from 1Ghz all the way to 2Ghz. Now that newer, faster processors have been introduced by AMD, you may find that your motherboard cannot run them due to changes in the architecture of the new chip, such as a differing voltage requirement. Or maybe you just need an updated BIOS (motherboard chip that controls the motherboard).
Some motherboards have a sound card and/or video board integrated into the motherboard itself. Whilst this can save you money, it can restrict you if you want to upgrade to a better sound or video card later. It's fine if you start off with integrated components as long as you can disable them at a later date (usually by fiddly, tiny connectors (aka jumpers) on the motherboard). It's worth noting that it's the cheaper end of the market that has integrated components built in.
The number of memory slots used to be an issue (it determined how much expensive memory could be added at a later date) but nowadays you get either 2, 3 or sometimes 4 slots for the memory. The bigger question is what sort of memory does the motherboards support?
There are 3 main sorts of memory available today: SDRAM, 133Mhz, known as PC133 (rapidly going out of favour), DDR, 266Mhz, known as PC2100 (faster and the most common form) and RAMBUS, 800Mhz (exclusively for Intel P4 based processors, very fast but very expensive). DDR is available in two main speeds: 266Mhz (PC2100) and the newer 400Mhz (PC2700). Your motherboard may well support different speeds and even types of memory. DDR is the best choice today, although that will undoubtedly change over time.
Expansion (PCI) slots
Expansion slots (aka PCI slots) determine how many extra components you can add to your motherboards. "Components" in this case means Sound Card, Network Card, TV Card, Video In (from your camcorder perhaps). If you have integrated sound, video and network cards on board then you need fewer slots for expansion. If you decide in 12 months that you absolutely need another slot for your Mega-hyper-beam-me-up-Scotty card then it's probably as well to get a new motherboard at the time rather than trying to "future proof" yourself now.
Every motherboard today comes with a special expansion slot for an AGP video card (unless you have video integrated and you then cannot upgrade). AGP cards are dealt with elsewhere. Warning: Integrated video cards use the main motherboard memory for themselves too. Thus you will "lose" 4, 8, 16 32 or more megabytes (Mb) of memory to the video function. Your main memory is not very fast compared to dedicated video memory, so don't expect to play the latest games with an integrated video component (not very well, anyway).
All ATX motherboards conform to a certain specification: 2 x USB ports, mouse, keyboard, serial and parallel ports. Extras for watch out for are Disk (IDE) RAID, Firewire, Dual BIOS and 6 channel built in audio. For goodness sake ignore any mentioning of that dreaded word "over clocking". This allows you run the processor/memory/BIOS at a faster rate than for which is was designed. It used to be a cheap way of extending the life of your system but now that processors are commodity, throwaway devices it would be better to just buy a faster processor/motherboard combination than risk instability and incessant "tweaking" just to get a few more Mhz of power. You wouldn't try and tweak a 400BHP car engine to get an extra 10BHP would you, whereas if all you had was 60BHP to start with and could end up with 70 BHP it could be viewed as worthwhile.
My recommendation: buy a motherboard with good web site support. There you will be able to download newer BIOS versions and patches which the manufacturer makes available. Of course you may never need this support but if you don't have it you can never get it when you do need it. Secondly, choose a sensible combination of PCI slots, memory slots and integrated components. Integrated sound is fine unless you intend to run a home cinema setup, 5 PCI slots will suffice for your needs, and 3 DDR memory slots will be adequate unless you intend loaning your PC to NASA. I can't recommend integrated video (graphics) cards because far better ones are available cheaply and won't steal your main memory. Update: motherboards are now appearing with inbuilt nForce2 graphics capabilities - I've tried one (the MSI K7N2G-L) which has excellent graphics performance, even if it does use some of your main memory. So my previous reservations are hereby withdrawn!
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