Question

where does the fetch part of the cycle get its instruction from? how does it know exactly ehere to go? explain your answer in deatil

Answer 1

Fetch

The Program Counter starts at OOOO. This means that the first address in RAM where the computer will look for instruction is at 0000.

The computer needs somewhere to store the current address in RAM that it is looking for. This is what the Memory Address Register (MAR) is for. 0000 is therefore copied into the MAR. A signal is now sent down through the Address bus to the RAM. The Control Unit sends out a memory read signal, and the contents of the address 0000 are copied through the data bus to the Memory Data Register.

As the data fetched during the fetch stage is an instruction, it is copied into the Instruction Register (IR).As the first instruction has been fetched, the system is at the end of the Fetch stage of the cycle. The program counter can be incremented by 1, so the system is ready to read the next instruction when the next Fetch cycle starts.