RAM is one of the most important components in a computer. It determines how fast your system will run when operational. This is where the computer temporarily stores data for quick access. If you run out of RAM, the computer uses hard drive space (virtual memory). Because of its importance, this is one part you need to consider carefully when you build your computer. The latest DDR2 RAM comes in matched pairs (called kits). These matched pairs go into dual channel (corresponding colour) RAM slots which make the transfer speeds double what it would have been. The latest DDR3 RAM comes in triple channel kits which actually triple the transfer speed. This dual and triple channels are recommended to get the maximum performance from your system. It is recommended that the RAM be the same make, speed and capacity.

Firstly, the amount of RAM you need differs. With the release of Vista, you need at least 2GB of RAM to run aero and decent games. If you do a lot of photo editing and intense gaming, you may want to consider 4GB of RAM. Today, RAM is quite cheap, especially DDR2. You can get some decent 2GB memory for about AUD$65.

Secondly, What type of RAM do you need? Recently, DDR3 RAM was released. It is still quite expensive and offers little performance improvement for now but if you want to run your computer at its peak then this is the RAM to go for. If you are an average user, DDR2 is the way to go. It is dirt cheap and offers good performance. If you have an old system, DDR is your only option but not very many company's make DDR RAM any more and it costs more than DDR2 because there is less demand for it. If your system still uses DDR RAM, you may want to consider upgrading.

One last thing you need to be careful with is the memory Latency. This is how quickly the RAM can request and receive data. The lower the number the better. It is usually put as something like 5-5-5-12 or 4-4-4-12. You want to look at the lowest number possible but with this, costs also go up. Also, the latency goes up depending on the RAM type and speed so while DDR2 has latencies of 5-5-5-12 and 4-4-4-12, DDR3 might have latencies like 8-8-8-15. As long as you do your research beforehand, you should be alright. It isn't too much of a performance gain though so if maximising the speed doesn't take priority over the price of the product, then this shouldn't sway you too much.

Please note that although Windows 7 32-bit edition says that it can handle 4GB of RAM, this is the total RAM in the system - including video memory (if you have a video card) and sound memory (if you have a sound card). For example if you had 4GB of RAM and a 512MB video card, you would only be able to use 3.5GB of your RAM. If you don't need to squeeze every inch of performance out of your computer, to save money just buy 3GB of RAM. However if you need the full 4GB then consider Windows 7 64-bit edition. But do your research carefully as not all companies release 64-bit drivers