The fetch-execute cycle in detail

Overview

Three phases of the fetch-execute cycle, clock speed of a processor and interrupt, in the context of the cycle.

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

   State the three phases of the fetch-execute cycle.

   Model answer

   Fetch, decode and execute.

2. 2

   What happens first in the fetch phase?

   Model answer

   The address in the program counter is copied to the memory address register.

3. 3

   What happens after the address reaches the memory address register?

   Model answer

   The contents of that location are fetched over the data bus into the memory data register.

4. 4

   When is the program counter incremented?

   Model answer

   During the fetch phase, once the address has been issued, so that it points to the next instruction.

5. 5

   Where is the fetched instruction placed for decoding?

   Model answer

   In the current instruction register.

6. 6

   What happens in the decode phase?

   Model answer

   The control unit interprets the opcode to determine which operation is required and where its operands are.

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