The task of the CPU is to process data and follow instructions.
But it must also be able to react to events as they occur, regardless of what it is doing at the time. For example when the mouse is moved, the pointer on the screen needs to respond and move accordingly.
There are two methods of dealing with events.
The first is 'polling' and the second is the use of 'interrupts'.
These will be discussed over the next few pages.