Q7Computer Architecture
Question
Q.7. Mention the various phases in executing an instruction.
Answer
The phases of instruction execution are: Fetch (retrieve instruction from memory), Decode (interpret opcode and operands), Execute (perform the operation), and Store/Write-back (save the result), often followed by updating the program counter.
The standard instruction execution cycle comprises four principal phases: Fetch, in which the instruction pointed to by the Program Counter (PC) is retrieved from memory into the Instruction Register (IR), and the PC is incremented; Decode, in which the control unit interprets the fetched opcode to determine the operation and identify the operands/addressing mode required; Execute, in which the ALU or other functional unit actually performs the specified operation (arithmetic, logic, memory access, or branch); and Write-back (Store), in which the result of the execution is written back to a register or memory location, completing the cycle before the next instruction fetch begins.