uniprocessor

A uniprocessor is a computer system that contains a single central processing unit (CPU) responsible for executing instructions. In such systems, there is only one instruction stream at a time, and parallel work is achieved primarily through time-sharing and context switching performed by the operating system rather than by hardware-based parallelism.

Hardware and memory in a uniprocessor system include a single CPU core that executes instructions, a shared memory hierarchy, buses, and input/output subsystems that connect peripherals. Concurrency appears as multiple tasks being scheduled over time; the processor may use pipelines and caches, but there is no second CPU to run instructions simultaneously.

Performance considerations for uniprocessors center on the lack of true simultaneous execution. Throughput depends on clock speed, pipeline efficiency, cache performance, and I/O latency. Modern operating systems use preemption and context switches to keep the CPU busy, but heavy parallel workloads benefit from multiprocessor or multi-core designs.

Usage and historical context: Uniprocessor systems were dominant in early computers and remain common in many embedded devices. They continue to be used in simple microcontrollers and real-time applications where deterministic timing and low cost are priorities. For general-purpose computing, scalable performance often requires multiprocessor architectures.

Relation to cores and virtualization: A uniprocessor system has one CPU, regardless of how many cores a modern processor exposes; a single processor unit may still have multiple cores, but true parallelism is limited to one CPU. Many systems once classified as uniprocessor have migrated to multi-core or multi-processor configurations, while software may still be written for single-processor environments.