| Pipeline (computer) |
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Computer-related pipelines include:
CONCEPT AND MOTIVATION Pipelining is a natural concept in everyday life, e.g. on an assembly line. Consider the assembly of a car: assume that certain steps in the assembly line are to install the engine, install the hood, and install the wheels (in that order, with arbitrary interstitial steps). A car on the assembly line can only have one of the three steps done at once. After the car has its engine installed, it moves on to having its hood installed, leaving the engine installation facilities available for the next car. The first car then moves on to wheel installation, the second car to hood installation, and a third car begins to have its engine installed. If engine installation takes 20 minutes, hood installation takes 5 minutes, and wheel installation takes 10 minutes, then finishing all three cars when only one car can be operated at once would take 105 minutes. On the other hand, using the assembly line, the total time to complete all three is 75 minutes. At this point, additional cars will come off the assembly line at 20 minute increments. COSTS AND BENEFITS As the assembly line example shows, pipelining doesn't decrease the time for a single datum to be processed; it only increases the Throughput of the system when processing a stream of data. A pipelined system typically requires more resources (circuit elements, processing units, computer memory, etc.) than one that executes one batch at a time, because its stages cannot reuse the resources of a previous stage. Moreover, pipelining may increase the time it takes for an instruction to finish. DESIGN CONSIDERATIONS One key aspect of pipeline design is balancing pipeline stages. Using the assembly line example, we could have greater time savings if both the engine and wheels took only 15 minutes. Although the system Latency would still be 35 minutes, we would be able to output a new car every 15 minutes. Another design consideration is the provision of adequate buffering between the pipeline stages — especially when the processing times are irregular, or when data items may be created or destroyed along the pipeline. SEE ALSO
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