Interrupts

Question 1

What is an interrupt?

Answer 1

A signal for the CPU to top what it is doing and carry out the interrupt task, carried out by the interrupt service routine

Question 2

Input/Output Interrupt

Answer 2

generated by the I/O devices to signal a job is complete or an error has occurred

Question 3

Timer Interrupts

Answer 3

Generated by an internal clock to signal that the processor should attend a time critical activity

Question 4

What is the Interrupt Service Routine?

Answer 4

The part of the OS which is responsible for dealing with interrupt signals. A program with a set of instructions that need to be FDE to carry out the operations of the interrupt

Question 5

How does the ISR work?

Answer 5

All previous tasks are placed in a stack.
The ISR places the interrupt into a queue as necessary.
Once the interrupt is complete, the pervious tasks are brought back from the stack.

Question 6

Objectives of the ISR

Answer 6

• Maximise the use of the whole computer system
• Be fair to all users
• Provide reasonable response time to all users
• Prevent the system failing or becoming overloaded
• Ensure the system is consistent by giving similar response times to similar jobs

Question 7

Software Interrupts

Answer 7

Detect and fix errors. They prevent crashes caused by unexpected conditions