CPU components and the fetch-execute cycle

Overview

The purpose of the CPU, the fetch, decode and execute stages, the ALU, Control Unit, cache and registers, Von Neumann architecture, and what the MAR, MDR, Program Counter and Accumulator hold.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is the purpose of the CPU?

   Model answer

   The CPU processes the instructions and data that make a computer system work. The CPU does this by repeatedly carrying out the fetch-execute cycle.

2. 2

   What happens during the fetch stage of the fetch-execute cycle?

   Model answer

   The next instruction is copied from main memory into the CPU, using the address held in the Program Counter. The Program Counter is then incremented to point to the following instruction.

3. 3

   What happens during the decode stage of the fetch-execute cycle?

   Model answer

   The Control Unit interprets the fetched instruction to work out what it means. The CU then prepares the parts of the CPU needed to carry it out.

4. 4

   What can happen during the execute stage of the fetch-execute cycle?

   Model answer

   The CPU carries out the decoded instruction. Execution may involve an ALU calculation, reading from or writing to memory, or jumping to another instruction.

5. 5

   What does the ALU do?

   Model answer

   The Arithmetic Logic Unit performs calculations such as addition and subtraction. The ALU also carries out logical operations and comparisons, such as checking whether one value is larger than another.

6. 6

   What is the role of the Control Unit?

   Model answer

   The Control Unit decodes instructions and sends control signals to coordinate the other parts of the CPU. The CU also controls the flow of data between the CPU and memory.

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