1.1.1 (2) - Fetch-Execute Cycle

What are the 5 main examples of registers?

PC, ACC, MAR, MDR and CIR.

What is the purpose of each register?

• PC holds the memory location address of the next instruction to be fetched and executed.

• ACC holds the results of calculations.

• MAR holds the address in memory where data is to be fetched or stored.

• MDR holds the data just been fetched or about to be stored

• CIR holds the current instruction

What happens in the ‘Fetch’ part of the cycle?

The next instruction is fetched from memory.

What happens in the ‘Decode’ part of the cycle?

The instruction is interpreted/decoded by the CU.

What happens in the ‘Execute’ part of the cycle?

The instruction is carried out.