Fetch Decode Execute cycle

Question 1

What is the FDE cycle?

Answer 1

It is the cycle that the CPU carries out to execute an instruction

Question 2

List the steps of the Fetch part of the FDE cycle (remembering to mention the buses).

Answer 2

1. Value of PC is copied into the MAR (Data Bus)
2. The address stored in the MAR is searched for in the main memory (Address Bus)
3. The instruction found in main memory is copied into the MDR (Data Bus)
4. Instruction copied to CIR (Data Bus)
5. Value of PC increments by 1

Question 3

List the steps of the Decode part of the FDE cycle (remembering to mention the buses).

Answer 3

1. CIR splits the instruction into ‘operator’ (the first half) and ‘operand’ (the second half)
2. Whether the operator is in the CPU’s instruction set or not (what the CPU can do) is verified.
3. The action to execute is found (in the instruction set)

Question 4

What is the Von Neumann Architecture?

Answer 4

A system in which the CPU runs programs off main memory (RAM)