Comparison To Prior Parallel Paradigms
Basic computers started from a sequential execution paradigm. Traditional CPUs are SISD based, which means they conceptually perform only one operation at a time. As the computing needs of the world evolved, the amount of data to be managed increased very quickly. It was obvious that the sequential programming model could not cope with the increased need for processing power. Various efforts have been spent on finding alternative ways to perform massive amounts of computations but the only solution was to exploit some level of parallel execution. The result of those efforts was SIMD, a programming paradigm which allowed applying one instruction to multiple instances of (different) data. Most of the time, SIMD was being used in a SWAR environment. By using more complicated structures, one could also have MIMD parallelism.
Although those two paradigms were efficient, real-world implementations were plagued with limitations from memory alignment problems to synchronization issues and limited parallelism. Only few SIMD processors survived as stand-alone components; most were embedded in standard CPUs.
Consider a simple program adding up two arrays containing 100 4-component vectors (i.e. 400 numbers in total).
Read more about this topic: Stream Processing
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