Structure and role of the processor and its components

Question 1

What is the system clock?

Answer 1

A device that generates a timing signal which changes at a regular frequency.

Question 2

What is the purpose of the system clock?

Answer 2

The signal is used to synchronise communication between the components of the processor and the rest of the computer system.

Question 3

What is the fetch execute cycle?

Answer 3

A continuous cycle performed by the processor, consisting of three stages.
Fetch
Execute
Decode

Question 4

What occurs in the fetch stage of the cycle?

Answer 4

The next instruction to execute is retrieved from main memory

Question 5

What are the steps involved in the fetch cycle?

Answer 5

1. The content of the PC is copied to the MAR
2. The content of the MAR is transferred to main memory by the address bus
3. The instruction is sent from main memory to the MBR by the data bus
4. The PC is incremented by one
5. The content of the MBR is copied to the CIR

Question 6

What occurs in the decode stage?

Answer 6

The fetched instruction is decoded

Question 7

What are the steps involved in the decode stage?

Answer 7

1. The content of the CIR is decoded by the control unit

2. The decoded instruction is split into two parts: opcode and operand.

Question 8

What is the opcode?

Answer 8

Specifies the operation to be carried out

Question 9

What is the operand?

Answer 9

Data on which the operation is performed

Question 10

What happens in the execute stage of the cycle?

Answer 10

Instruction is carried out in the execute stage of the cycle

Question 11

What are the steps involved in the execute stage of the cycle?

Answer 11

• Any data required by the instruction that isn’t present in the registers is fetched
• The instruction is carried out
• Results of any calculations are stored in general purpose registers or main memory

Question 12

What happens to the status register?

Answer 12

Between each execute stage and fetch stage of the cycle, the content of the status register is checked for changes that could signify the occurrence of an interrupt

Question 13

What is a processor’s instruction set?

Answer 13

group of instructions it can carried out, each type of processor has its own instruction set.

Question 14

Why might one instruction not be compatible with another processor?

Answer 14

Each type of processor has its own instruction set, so instructions for one processor may not be compatible with other processors.