Why is a power failure interrupt treated as the most urgent?

A power failure leaves only milliseconds before the contents of main memory are lost. The operating system must save the current state within that time.

Why is a fast device given a higher priority than a slow one?

A fast device refills its buffer very quickly and loses data if it is ignored. A slow device can wait without anything being lost.

Explain why a printer running out of paper is a low priority interrupt.

The printer simply stops and nothing is lost while it waits. Attention a few milliseconds later has no effect on the outcome.

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Interrupts, Memory Management and Scheduling

Interrupt priorities and how they are allocated

3 things to know
Component 2

Overview

Three factors that decide the priority given to an interrupt, non-maskable interrupt and danger of giving every interrupt the same priority.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why do interrupts need priorities?

Key term

Which kind of interrupt is normally given the highest priority?

Key term

State three factors that decide the priority given to an interrupt.

Questions from this subtopic

Each one with the model answer underneath.

1
Why do interrupts need priorities?
Model answer
Several devices may signal at the same moment. Priorities decide which event is dealt with first and which can safely wait.
2
Which kind of interrupt is normally given the highest priority?
Model answer
A hardware failure such as loss of power is given the highest priority of all. The system has only a moment to save its state before it stops.
3
State three factors that decide the priority given to an interrupt.
Model answer
The urgency of the event and the damage a delay would cause both decide the priority. The speed of the device involved is a third factor.
4
Why is a power failure interrupt treated as the most urgent?
Model answer
A power failure leaves only milliseconds before the contents of main memory are lost. The operating system must save the current state within that time.
5
Why is a fast device given a higher priority than a slow one?
Model answer
A fast device refills its buffer very quickly and loses data if it is ignored. A slow device can wait without anything being lost.
6
Explain why a printer running out of paper is a low priority interrupt.
Model answer
The printer simply stops and nothing is lost while it waits. Attention a few milliseconds later has no effect on the outcome.

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