Central Processing Unit

Central Processing Unit (CPU) is the component of a computer that interprets instructions, performs arithmetic and logical operations, and coordinates the flow of data between memory and peripheral devices. In a von Neumann machine, the CPU comprises a control unit that fetches and decodes instructions, an arithmetic logic unit that executes operations, and registers that hold intermediate results. The CPU is the locus of sequential computation: it is where the stored program becomes executed behavior.

The performance of a CPU is determined by the interplay of clock frequency, instruction set architecture, microarchitecture, and memory hierarchy. Clock frequency — the rate at which the processor executes steps — is no longer the primary metric of performance. Modern CPUs exploit instruction-level parallelism, speculative execution, and deep cache hierarchies to execute multiple instructions simultaneously and out of order, masking the latency of memory access. The result is that the effective performance of a processor can be an order of magnitude higher than its nominal clock speed would suggest.

The CPU is also the site of the most intense physical constraints in computing. Power dissipation scales with frequency and voltage; as transistors shrink, static leakage current becomes comparable to dynamic switching power. The design of a modern CPU is therefore simultaneously an exercise in logical architecture and in thermal engineering. The processor is not merely a digital device. It is a heat source that happens to compute.