How does a computer work? Part one.

This is the Motherboard, it connects all the components together. Some are built into it, some connect directly onto it, the rest are connected to it by wires.

A typical motherboard
a typical motherboard

The large, white square in this picture houses the central processing unit (CPU or processor), that's the brain of the computer, it performs all the calculations but can't remember much. There are many different types (eg. Athlon, Pentium 4, Intel Celeron). The computer is often rated by its processor speed (eg. 3.2 gigahertz (GHz), 1.4GHz, 700MHz).

A typical CPU
a typical CPU

While the CPU is calculating it stores information temporarily in random access memory (RAM), this is 'volatile' memory, meaning that it can only hold information while there is power going to it. When the computer is switched off, RAM is completely reset.

RAM is measured in megabytes or even gigabytes, it can seriously affect the speed of the computer, it's good to have lots of RAM for processing images or encoding video. Typical values are 64MB (Windows XP will just run with this much), 256MB, 512MB (half a 'gig'), 2 or even 4 gigabytes.

A Hard Disk Drive (hard drive, hard disk, HDD)

This is the storage area of the computer where all your documents are stored as well as the operating system (OS, eg. Windows) and all the information your computer needs to run. Typical sizes are 20, 40, 80, 120 gigabytes, RAM also uses some hard disk space to temporarily store information. If the hard disk runs very low on space it can cause the computer to slow down because the RAM won't be able to use it.

Running order of a computer calculation:
The CPU starts calculating, it holds some data in RAM (actually there is some very fast RAM 'on chip' which it uses first, when that is full it goes on to RAM). When RAM is full it sends some data on to the hard disk in what is called a swap file. When the CPU is free it asks for the numbers back from RAM, RAM then has some free space so it reads some of what it sent to the hard disk. A typical swap file is about 500MB