What causes an interrupt

Overview

Four broad categories of interrupt, hardware failure interrupt and interrupt does a user pressing a key generate.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is an interrupt?

   Model answer

   An interrupt is a signal sent to the processor asking it to suspend its current work. The processor deals with the event and then resumes what it was doing.

2. 2

   Name the four broad categories of interrupt.

   Model answer

   The four categories are hardware failure, program error, input or output, and timer interrupts. Each category names the source of the signal rather than its urgency.

3. 3

   Give two examples of a hardware failure interrupt.

   Model answer

   A failure of the power supply raises a hardware interrupt. A memory parity error raises a second kind.

4. 4

   Give two events that generate an input or output interrupt.

   Model answer

   A printer signalling that it has run out of paper generates an input or output interrupt. A disc drive reporting a completed transfer does the same.

5. 5

   What is a timer interrupt used for?

   Model answer

   A timer interrupt is generated at fixed intervals by a hardware clock. The operating system uses it to end the time slice of the running process.

6. 6

   Give three program errors that raise an interrupt.

   Model answer

   An attempt to divide by zero raises an interrupt. An illegal instruction and an address outside the process's own memory do the same.

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