Fetchexecute

Fetch-execute is a foundational concept in computer architecture describing the basic cycle by which a central processing unit (CPU) processes instructions. In its simplest form, the cycle involves fetching an instruction from memory, then executing the operation specified by that instruction. This abstraction helps explain how a program is turned into a sequence of actions performed by the processor.

During the fetch phase, the CPU uses the program counter to locate the next instruction in memory, retrieves it, and often stores it in an instruction register. In the execute phase, the CPU decodes the instruction to determine the required operation, fetches any necessary operands from registers or memory, performs the operation (for example, an arithmetic or logical action), and writes results back to a destination such as a register or memory. The program counter is then updated to point to the subsequent instruction.

In modern processors, the simple fetch-execute model is expanded through pipelining, parallelism, and advanced techniques such as speculative and out-of-order execution. These features allow overlapping of fetch, decode, and execute across multiple instructions, increasing throughput but also introducing complexities like hazards and branch prediction challenges. The fetch-execute view remains a useful educational abstraction for understanding how instructions are processed at a high level, even as real hardware implements more sophisticated and optimized forms of the instruction cycle.

Historically rooted in early stored-program computers, the fetch-execute concept underpins many explanations of how software gets executed on hardware and is complemented by discussions of related ideas such as the fetch-decode-execute cycle and instruction pipelines.