Memory

The larger a computer‘s memory, the more space it has to put running programs. If the memory runs out of space, the computer will start using the hard drive as 'virtual memory' which is extremely slow.

More memory will not make your computer faster, but it will mean that you can open a greater number of things at once (programs, pictures etc) without the computer slowing down. These days, a minimum of 1GB is a must, 2GB is recommended, and for high end usage like professional graphics or gaming, 4GB is more suitable (remember if you have 4GB or more you will need a 64bit operating system, such as Windows Vista64).

Memory communicates with the processor via the FSB, so the faster your memory is the more information it can send and receive from the processor. Speed is usually rated in one of two ways. The first is the raw clock speed, for example 'DDR2 -800MHz' (i.e. 800MHz). The second is bandwidth, which indicates the amount of information that can be pumped through it per second (in MB). For memory running at 1066MHz this would be written as 'PC2-6400' (i.e. 6400MB/s)

However this is only true up to a point. Once the speed of memory reaches about 3/4 the speed of the FSB, the performance benefits become negligible. In fact because faster memory usually has higher 'latency' (see below) it can actually decrease performance. As a rough guide go for memory that is around 3/4 the speed of your FSB. So if your FSB is 1333MHz, then memory running at 800MHz or 1066MHz would be good choices.

The topic of memory and FSB speed is a very complex and controversial one. Some will say that it is better to have both running in a 1:1 ratio (effectively memory which is 1/2 the speed of the FSB), whereas others will argue it is faster to have a memory speed closer to the actual FSB (i.e. 1333MHz memory for a 1333MHZ FSB). Ultimately you will notice very little difference either way in terms of every day performance.

Latency is the time it takes memory to retrieve a given piece of information after the Processor asks for it. The lower the latency the faster memory can react to the processors needs. It is measured in cycles, so a latency ofcas5 would mean that the memory has to run 5 clock cycles before it can pass the information over the FSB. You may see the latency written as 4 numbers divided by dashes (e.g. 4-4-4-12). These are the 4 types of latency, the first being the most important 'cas '. Lower numbers are always better. Generally the faster the memory speed, the larger the latency. This can have a dramatic effect on memory performance, which is why running memory which has a slower clock speed but lower latencies can give better results than higher clock speeds with higher latencies.

Currently DDR2 and DDR3 are the available memory types. Other than higher speeds, DDR3 offers nothing new over DDR2 and is considerable more expensive, so unless you need the higher speed, stick with DDR2.

Whichever memory type you choose, remember that your motherboard must support it. Most motherboards will only support 1 type of memory, be it DDR2 or DDR3.

The term 'dual channel' refers to a feature of memory where twice as much information can be passed through when 2 modules of the same size are installed in a motherboard that supports it.

All new motherboards have the capability to run in dual channel mode, and we recommend you take advantage of it. Just buy your memory in 2 modules instead of one, if you want 4GB then buy 2 x 2GB modules.

A memory module with heatsink attached

Some higher end memory modules come with heat sinks attached. These will dissipate heat more quickly, meaning the memory stays cooler under load and gives more potential for overclocking.