decodeexecute

The decode execute cycle, also known as the instruction cycle or fetch-decode-execute cycle, is a fundamental process in computer architecture that describes how a CPU processes instructions. It is a continuous loop that the processor repeats to execute programs. The cycle consists of three main stages.

The first stage is fetch. In this phase, the CPU retrieves the next instruction from memory. The program counter (PC), a special register within the CPU, holds the memory address of the next instruction. The instruction is then fetched from that address and loaded into the instruction register (IR). After fetching, the PC is incremented to point to the next instruction in sequence.

The second stage is decode. Once the instruction is in the IR, the CPU's control unit decodes it. This involves interpreting the instruction's opcode and operands to determine what operation needs to be performed and on what data. The control unit generates the necessary signals to carry out the decoded instruction.

The third stage is execute. During this phase, the CPU performs the operation specified by the instruction. This could involve arithmetic or logical operations, data movement between registers and memory, or control flow changes like jumps or branches. The results of the execution are then stored in registers or memory as required. After the execute stage, the cycle begins again with the fetch stage, ready to process the next instruction. This constant repetition allows the computer to run software.