4. Operating systems and computer architecture

Question 1

Functions of an operating system

Answer 1

Controls inputs and outputs
Controls interrupts
Security (log on)
Memory management
Error handling
Loading software

Question 2

What is an interrupt?

Answer 2

A signal sent from a device or software to the processor to cause it to temporarily stop.

Question 3

When is an interrupt used?

Answer 3

When a disk drive is ready to receive more data
An error has occurred
When the user presses ctrl alt del
A software error has occurred

Question 4

What do interrupts allow computers to do?

Answer 4

Appear to do many things at the same time e.g. have several windows open at the same time

Question 5

What is the purpose of an interrupt handler?

Answer 5

Stores the progress on each task when an interrupt is used and the computer does something else

Question 6

What is a buffer?

Answer 6

A temporary memory area used to store data when hardware or the internet is running slower than the processing speed of the computer.

Question 7

What is the purpose of an address bus?

Answer 7

Carries signals relating to the location of data between the processor and the memory

Question 8

What is the purpose of a data bus?

Answer 8

Sends data between the processor and memory and the input/output devices.

Question 9

Control bus

Answer 9

Carries signals relating to the control and coordination of all activities with the computer.

Question 10

What is an MAR?

Answer 10

Memory address register - stores the address of the next register to be read.

Question 11

What is an MDR?

Answer 11

Memory data register - stores the contents of the address in the MAR.

Question 12

What is the ALU?

Answer 12

Arithmetic and logic unit -where instructions are carried out.

Question 13

What is the PC?

Answer 13

Programme counter - keeps track of which register is being looked at next.

Question 14

What is the CIR?

Answer 14

Current instruction register - stores the current instruction.

Question 15

How does the fetch decode execute cycle work?

Answer 15

1. The PC contains the address of the next instruction which has to be fetched.
2. The address is copied into the MAR using the address bus.
3. The instruction at the location in the MAR is stored in the MDR.
4. The instruction in the MDR is copied into the CIR.
5. The value in the PC is incremented by 1.
6. The instruction is decoded and executed.