Case

Cases come in two main types, desktop (sometimes called pancake or pizza style) and tower. Tower cases are either full height (approximately 62 cm high), midi (42cm high) and mini (35cm high). You should specify a case large enough to hold all the components that you are planning to use. It is important that you choose an ATX style case, which refers to the type of motherboard that we are going to use. The case usually comes with an integral Power Supply Unit, which must be correctly rated for the type of components that you are going to install.

Motherboard

The motherboard is crucial. It is the component that links all of the PC components together using a whole range of technologies. Make sure that you choose a motherboard that is compatible with the kind of processor that you have bought, the graphics card that you will be using, and that it has enough PCI slots for the "goodies" that you are going to install. Some motherboards support USB 2.0 or Firewire which provide extremely fast data transfer, and use UDMA 100 data buses for connecting high speed hard drives.

The motherboard may also offer on board sound, on board video, on board modem and on board LAN connections. All of these features are useful, except for the on board video because you will almost certainly need a higher specification dedicated graphics card.

Graphics Card

Most motherboards need a separate graphics card. There are many different models and new developments mean that the specification of graphics cards are improving constantly. The graphics card is actually a sophisticated computer system in it own right, and contains all the components of a computer system. The card has a large amount of on board memory, often as much as 128 Mbytes.

Sound Card

It is very common to have a motherboard with a built in sound card. Whilst this will be adequate for most users, you may want to buy a more advanced card. These offer a large range of features, and most cards include games controller ports, microphone input, and additional features such as optical connections to advanced sound systems.

Processor

It is not my intention to debate the merits of various types of processor, basically you have two main options, Intel and AMD. I have built several systems now, and have always used Intel processors. Whenever somebody describes a problem with a system that they have configured themselves, they have used an AMD Athlon chip, so my conclusion is that Intel is safe and Athlon is not! Whatever processor you use, you should make sure that the case that you have specified includes a power supply unit (PSU) that is correctly rated for the processor. Athlons, in general, use more power, create more heat, and are slightly cheaper than Intel. AMD are also winning the "fastest" processor war at the moment.

Memory

Once upon a time, many moons ago, the only decision that you needed to make regarding memory was how much could you afford! There are now several different types, and the price has fallen considerably. Check which kind your motherboard manufacturer recommends and buy as much as you can afford.

The memory is also available to run at different clock speeds and you should match the memory speed to the motherboard clock frequency.

Have a look at more facts about computer memory by clicking on this link

Hard Drive

The Hard Drive is an extremely important part of your system. It is obliviously the main non volatile storage (it doesn't"forget" when you turn it off), but it is also in constant use, accessing work files, temporary files, loading the Operating System, etc. The speed of your hard drive is critical, and you should purchase the fastest drive that you can afford and your motherboard supports. Currently UDMA 100 capable motherboards with UDMA 100 hard drives running at 7200 rpm provide quite a high performance.
As for size, go for the largest drive that you can afford! You should bear in mind that there are currently some issues surrounding drives larger than 127Gigabytes.

CDROMs etc

A CD drive of some description is essential. You can now buy combined CDRW/DVD drives quite cheaply which will allow you to use the CDRW drive as a backup storage device. It is also useful to have a normal CD ROM drive as well as the CDRW, but check that your motherboard has enough IDE connections to allow this.

Floppy disks are also useful, and for about a fiver, they are not worth missing off!