Pipelined

Pipelined is an adjective used to describe systems or processes that operate as a pipeline, where a task is broken into discrete stages and each stage processes a portion of the task in sequence. While a single task passes through the stages, other tasks can begin at the first stage, so multiple tasks are in different stages at once, increasing throughput compared with a non-pipelined, sequential approach.

In computer architecture, instruction pipelining is a common form. A typical five-stage pipeline includes instruction fetch, decode, execute, memory access, and write-back. At steady state, one instruction completes per cycle, even though individual instructions may take several cycles to finish. The maximum achievable throughput depends on the balance among stages and memory delays. Pipelining can also be applied in data paths, graphics processing, and other hardware designs to improve performance.

Pipelines face hazards that can cause stalls or incorrect results. Data hazards occur when instructions depend on the results of previous ones; control hazards arise from branches; structural hazards occur when hardware resources are insufficient. Techniques to mitigate hazards include data forwarding (bypassing), pipeline stalls, and branch prediction. Some designs use out-of-order execution or speculative execution to hide latencies.

Pipelining is not limited to CPUs. In digital signal processing and data processing workflows, pipelines link a sequence of processing blocks so that data continuously flows through. Software pipelining is a software technique that reorganizes code to improve instruction-level parallelism, while hardware pipelines operate at runtime.

Advantages include higher throughput and efficient resource use; disadvantages include increased latency per task, sensitivity to imbalance between stages, and design complexity. Pipelined designs have become standard in modern processors and other high-throughput systems.