4.7.3.1 The processor and its components

Question 1

What is the purpose of the Control Unit?

Answer 1

It manages the execution of instructions by synchronising the operation of the processor using the inbuilt clock. It sends control signals to other components to help fetch, decode and execute instructions and control the transfer of data.

Question 2

What is the purpose of the Arithmetic Logic Unit?

Answer 2

Carries out arithmetic and logical instructions and is a gateway to the processor

Question 3

What is a register?

Answer 3

A very fast memory location in the processor
They can be general purpose, used as memory locations to store data and instructions, or special purpose, one that has a data handling task.

Question 4

What does the Program Counter do?

Answer 4

Contains the address of the next instruction to be carried out. It controls the order of the execution of instructions and is incremented after being read.

Question 5

What does the Memory Address Register do?

Answer 5

Contains the address of the next location to be accessed in memory, often copied from the PC or the CIR

Question 6

What does the Memory Data / Buffer Register do?

Answer 6

Contains the contents of the address specified in the MAR, the data currently being used by the processor.

Question 7

Why is the Current Instruction Register needed?

Answer 7

Holds the instruction whilst it’s being decoded and executed, split into the opcode and operand. It may be copied to the MAR if it’s an address and to the MDR if it’s data

Question 8

When may the status register have a bit set?

Answer 8

Arithmetic results
Interrupt
Parity
Halt