Learning Objectives

Interrupts

• This is a signal to a processor indicating that an asynchronous event has occurred.
• Here the current sequence of instructions is temporarily suspended, and a sequence appropriate to the interruption is started in its place.
• Its purpose is to alert the operating system when any special event occurs so that it can suspend its current activity and deal appropriately with the new situation

Interrupts… incoming…

• Usually an interrupt gives a signal from a device attached to a computer or from a program within the computer that causes the main program that operates the computer (the operating system) to stop and figure out what to do next.
• Almost all personal (or larger) computers today are interrupt-driven - that is, they start down the list of computer instructions in one program (perhaps an application such as a word processor) and keep running the instructions until either
• (A) they can't go any further or
• (B) an interrupt signal is sensed.
• After the interrupt signal is sensed, the computer either resumes running the program it was running or begins running another program.

Interrupts - Multitasking

• Basically, a single computer can perform only one computer instruction at a time. But, because it can be interrupted, it can take turns in which programs or sets of instructions that it performs.
• This is known as multitasking. It allows the user to do a number of different things at the same time.
• The computer simply takes turns managing the programs that the user effectively starts. Of course, the computer operates at speeds that make it seem as though all of the user's tasks are being performed at the same time.

Interrupts handler

• A code in operating system that prioritizes the interrupts and saves them in a queue if more than one is waiting to be handled.
• The operating system has another little program, sometimes called a scheduler, which figures out which program to give control to next.