4. RAM - Random Access Memory

A general purpose computer has to be able to store data. It has to have a 'memory'.

It is also essential that the control unit can get directly to any piece of data it needs i.e. it can access any memory location at random.

Not surprisingly then, this block is called 'RANDOM ACCESS MEMORY' or RAM as it is commonly known.

Random Access Memory is 'volatile memory'.  The data is held on a chip, but only temporarily.  The data disappears when the power is switched off. 

But it is extremely fast! It is thousands of times faster than a hard disk.

Have you ever forgotten to save your work before the computer crashed?  When you log back on, your work has disappeared.  This is because it was stored in RAM and was lost when the PC switched off.  However, if you had saved your work from RAM to the hard disk, it would have been safe!

Today, a humble PC typically holds 512 Megabytes of RAM. A more expensive machine can hold much more than this.

If you are a keen computer gamer, then it is not unusual to have 2 Gigabytes of RAM! This allows the graphics to stay in memory - so its much smoother to play.