Why interrupt can be used?
The majority of the different parts of the PC need to send information to and from the processor and they expect to be able to get the processor's attention when they require to doing this. The processor has to balance the information transfers it gets from different parts of the machine and ensure they are handled in an organized fashion. There are two essential ways that the processor could do this:
- Polling: The processor could acquire turns going to each device and asking if they have anything they require it to do. This is called as polling the devices. In a few situations in the computer world this technique is used, though it is not used by the processor in a PC for a couple of basic reasons. One reason is that it is wasteful obtainable around to all the devices constantly asking if they need the attention of the CPU wastes cycles that the processor could be doing something useful. This is particularly true for the reason that in most cases the answer will be "no". One more reason is that different devices need the processor's attention at differing rates the mouse wants attention far less frequently than say the hard disk (when it is actively transferring data).
- Interrupting: The other way that the processor is able to handle information transfers is to let the devices request them when they need its attention. This is the foundation for the use of interrupts. When a device has data to transfer it produce an interrupt that says I need your attention now please. The processor after that stops what it is doing and deals with the device that requested its attention. It actually is able to handle many such requests at a time using a priority level for every to decide which to handle first.