CPU & Architecture

What does the ALU do?

It performs arithmetic and logic operations such as addition, subtraction and logic checks (AND, OR, NOT)

What does the Control Unit (CU) do?

The Control Unit manages the movement of data in the CPU and tells other parts of the CPU what to do next. yeah

What are Registers?

Small, fast storage locations in the CPU used to temporarily hold data or instructions during processing

What does the PC do?

Holds the address of the next instruction to be fetched from memory

What does the Memory Address Register do?

It holds the address of the memory location to be accessed (for read or write).

What does the MDR do?

it holds the data being transferred to or from memory.

What does the accumulator do?

it stores the results of calculations carried out by the ALU and holds data for processing

Describe the steps involved in the fetch-decode-execute cycle in a Von Neumann CPU. Include the roles of the PC, MAR, MDR, buses, and other components. (6 marks)

1. The Program Counter (PC) holds the address of the next instruction.

2. The address is sent along the address bus to the Memory Address Register (MAR).

3. The instruction is fetched from memory via the data bus and stored in the Memory Data Register (MDR).

4. The instruction is copied into the Current Instruction Register (CIR), and the PC is incremented to the next instruction address.

5. The Control Unit (CU) decodes the instruction in the CIR.

6. The instruction is executed, which may involve the ALU, registers, memory, or input/output devices.

What is the Fetch-Decode-Execute Cycle?

The process where an instruction is fetched from memory, decoded by the control unit, and then executed by the CPU.

What happens in the fetch stage of the FDE cycle?

The instruction is fetched from memory using the PC and MAR; the instruction is stored in the MDR and copied to the Current Instruction Register.

What happens in the decode stage of the FDE cycle

The CU reads the instruction stored in the CIR and prepares the CPU for execution

What happens in the execute stage of the FDE cycle?

The CPU carries out the decoded instruction. the CU sends control signals using the control bus to control the required components

What is Pipelining? (benefits)

A technique where different stages of multiple instructions are overlapped. While one is being decoded the other is being executed or fetched. (Increases CPU efficiency by allowing more instructions to be processed per clock cycle, reducing time taken to carry out multiple FDE cycles