The stuff DRAMS are made of. Sorry! Memory is where the computer does its sums, essentially an area where data can be stored, retrieved and manipulated.

Most people call memory RAM which stands for Random Access Memory. It's not a particularly helpful acronym. It simply means that the computer can dive in and access any part of the memory, unlike a tape backup system, for example, where you might have to wade through meters of tape to reach a certain item of data.

RAM is volatile which means that when you remove the power, its contents is lost which is why you are taught from an early age to save often.

To confuse matters, there are several types of RAM and, as technology marches on, even more types are appearing. It's all about being able to shift more and more data with more and more speed.

The two main types of memory are SRAM (Static RAM) and DRAM (Dynamic RAM). SRAM retains its contents for as long as power is supplied to it. DRAM, however, only retains data for a few milliseconds, even under power.

Memory comes in all sorts of shapes and sizes and it's essential to get the correct memory chips for your system. Most current RAM types will be a type of DDR (Double Data Rate) although you may still come across SDRAM (Synchronous DRAM). The acronyms getting to you yet?

DDR2 (wait for it - Double Data Rate Two Synchronous Dynamic Random Access Memory) has been in use since around 2005. Without getting into the technicalities, it runs about twice as fast as DDR and generally needs less power.

The new kid on the block is DDR3 which, as you might imagine, runs even faster (around twice as fast as DDR2) but, as of writing, it's emerging technology, needs a motherboard that specifically supports it and currently it offers little advantage over DDR2. But that should change.

Obviously, the speed of the RAM is important if you want to get the best performance from your PC and, odd though it may sound, the same type of RAM from different companies does not necessarily run at the same rate. And different companies charge different prices for, what appears to be, similar chips.

RAM is one PC component that can be overclocked to increase performance but, as you may guess, not all RAM is capable of being overlocked to the same degree.

Even without overclocking, to get the most from your PC, If you're running Windows XP you should have a minimum of 1Gb RAM and if you're running Vista, 2Gb. Yes, the systems will run with less but it's like having a car with five gears and not getting out of third.

Other types of memory include ROM or Read Only Memory. This is a better acronym and it means that the computer can retrieve data from it but it can't write to it, like a finalised CD. There are lots of ROM chips in a computer, used to store set-up data and information which doesn't need changing. Data in ROM is permanent and remembered after switching off.

Flash memory lets you change its contents and remembers it after switching off. This is popular in modems, for example, cameras and, of course, USB flash drives.

There are also Flash Drives known as SSD (Solid State Drive/Disk) which use a type of memory rather than being a mechanical disk drive. Accessing data from a Flash Drive is faster than from a hard disk - but they are currently significantly more expensive.