Fetch decode Execute

Question 1

What happens in the fetch stage of the cycle

Answer 1

1.Program Counter (PC): The PC holds the memory address of the next instruction to be executed.
2.Memory Address Register (MAR): The contents of the PC (the address of the instruction) are copied to the MAR.
3.Address Bus: The address in the MAR is placed on the address bus, which sends the address to the memory location where the instruction is stored.
4.Data Bus: The instruction (data) at that memory location is read and placed on the data bus.
5.Memory Data Register (MDR): The instruction from the data bus is copied into the MDR.
6.Control Unit (CU): The CU then takes the instruction from the MDR and prepares it for decoding and execution.

Question 2

What happens in the decode stage of the cycle

Answer 2

1. Obtain the instruction:
   The CPU receives the instruction from the Current Instruction Register (CIR), which holds the instruction fetched from memory.
2. Identify the opcode:
   The CPU determines the type of operation (e.g., add, subtract, move) by analyzing the opcode part of the instruction.
3. Identify operands:
   The CPU identifies the operands, which are the data or memory locations the instruction will operate on.
4. Interpret the instruction:
   The CPU interprets the instruction based on the opcode and operands, determining what actions need to be taken.
5. Prepare for execution:
   The CPU prepares for the execution stage by setting up the necessary registers, memory addresses, and control signals.

Question 3

What happens in the execute stage of the cycle

Answer 3

The CPU receives the decoded instruction and performs the necessary operations, for example if it is mathematical, it uses the ALU, if instruction requires reading/writing data in memory, it uses the memory acess register

Question 4

Describe the role of the cache memory in the computer

Answer 4

It is a high speed memory that aids in the controlling of instructions, and the movement of data around the computer.