4. Memory and computer performance

It was mentioned that data and programs are stored in RAM, ready for use by the CPU. But there is only a limited amount of RAM available in any computer system. (Including the computer within the smart phone below).

What happens when you run out of memory? Answer: the computer stops running or 'crashes' unless the operating system deals with it intelligently - see below.

Therefore you must be careful that you work within the limitations of the RAM you have available. If you only have a modest amount of memory, then only open one or two applications at the same time. The more memory you have available the more applications you can have open at the same time.

Although the amount of RAM is limited, the operating system uses some clever tricks to make part of the hard disk appear as extra RAM. This is called 'virtual memory'. But it is very slow compared to 'real' RAM and so the operating system may give a warning such as 'you are low on virtual memory, please close some applications'.

You must have enough RAM installed in the computer to run the applications you intend use. This minimum is usually stated on the side of the box it came in. Even the operating system has to have a minimum amount of RAM for it to run.

A typical home computer will have about 1 to 4 Gigabytes of RAM whilst a supercomputer will have Terabytes in order to process a huge amount of data.