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Question 1

Fetch Stage

Answer 1

1. The Memory address stored by the program counter, which points to the next instruction to be fetched is copied to the MAR.
2. The address stored in the MAR is transferred to the main memory along the address bus.
3. The contents at the activated memory location is then copied to the MBR along the data bus, after which it is copied internally to the current instruction register (CIR) internally.
4. Finally the Program Counter is incremented so that it points to the next instruction to be fetched.

Question 2

Explain why the instruction could
not be processed directly from the MBR, during the decode and execute cycle.

Answer 2

The MBR is not directly wired to the components that will execute the instructions which the CIR is.