microarchitecture

Microarchitecture, or micro-architecture, refers to the way a given instruction set architecture (ISA) is implemented in a processor. It defines the structure and behavior of the processor's datapath, control logic, and memory hierarchy, and determines how instructions are executed rather than what they do. The microarchitecture is distinct from the ISA; multiple microarchitectures can implement the same ISA and remain backward compatible.

A typical microarchitecture includes a core datapath with registers, arithmetic and logic units, and execution units; a control unit that sequences operations; a pipeline that overlaps instruction stages; a cache hierarchy (L1, L2, and often L3) and a memory subsystem; branch prediction and speculative execution; out-of-order execution; instruction decode and retirement logic; and interconnects and coherence mechanisms for multicore systems. Modern designs may also include vector or SIMD units and hardware accelerators. The microarchitecture determines how well a processor uses its resources and how it handles parallelism, memory latency, and power.

Design goals frequently involve performance, power efficiency, die area, and thermal constraints. Techniques such as deep pipelining, superscalar execution, out-of-order processing, and speculative execution increase throughput but raise cost and power. Cache design, memory hierarchy, and branch prediction reduce stalls but add complexity. In multicore CPUs, cache coherence and inter-core communication are critical.

Historically, the term emerged to distinguish the implementation details from the ISA. Today, different vendors may share an ISA but pursue different microarchitectures to improve performance or efficiency. Notable examples include Intel’s optimized core designs, AMD’s Zen lineage, and ARM’s Cortex family.