RISC (Reduced Instruction Set Computer) is a CPU design philosophy that uses a small set of simple, uniform instructions that each execute in roughly the same amount of time. Instead of having specialized instructions for complex operations, RISC processors perform complex tasks by combining many simple instructions. The most prominent RISC architecture today is ARM, which powers virtually all smartphones and Apple's M-series chips.
Why it matters
Understanding RISC helps you grasp why different devices have different performance characteristics and why software compatibility varies. RISC processors typically achieve excellent performance per watt, which is why they dominate mobile devices where battery life is critical. The lesson CPU Architectures: x86, ARM, and RISC explores how these design choices affect the software you use every day.
How RISC works
RISC processors use instructions that are all the same size and typically complete in one clock cycle. This uniformity makes the processor's pipeline more efficient—the CPU can fetch, decode, and execute instructions in a smooth, predictable flow. While a RISC processor needs more instructions to perform a complex task compared to CISC, each instruction runs faster, often resulting in better overall performance.
RISC vs CISC
The main contrast is with CISC (Complex Instruction Set Computer), used in x86 processors. CISC processors have many specialized instructions that can do complex operations in a single step, but these take varying amounts of time to execute. In practice, modern processors have blurred these lines—x86 chips internally translate complex instructions into RISC-like micro-operations, and ARM chips have added some complex instructions for common operations.