Question

(c) briefly describe the processes in the fetch-decode-execute instruction cycle.

3 marks
total 15 marks

Explanation:

Fetch Phase

The CPU retrieves the next instruction's memory address from the Program Counter (PC), copies the instruction from main memory (RAM) into the Instruction Register (IR), and increments the PC to point to the subsequent instruction.

Decode Phase

The Control Unit (CU) interprets the binary instruction held in the Instruction Register, identifying the specific operation to be performed (opcode) and the locations of any required operands.

Execute Phase

The CPU carries out the decoded instruction, which may involve the Arithmetic Logic Unit (ALU) performing calculations, moving data between registers, or reading/writing data to memory.

Answer:

The fetch-decode-execute cycle consists of three main phases:

1. Fetch: The CPU retrieves the next instruction from the memory address stored in the Program Counter (PC) and loads it into the Instruction Register (IR). The PC is then incremented to point to the next instruction.
2. Decode: The Control Unit (CU) decodes the instruction in the IR to determine the required operation (opcode) and locate any necessary operands.
3. Execute: The CPU performs the decoded operation, which may involve calculations in the Arithmetic Logic Unit (ALU), data transfers between registers, or memory access.