Parallel Architectures 04/04/2007

Overview This paper is a rehash of a paper that appeared in 1972 “Some Computer Organizations and Their Effectiveness.” IEEE Transactions on Computers, C-21(9):948-960, September 1972. Four basic parallel computer taxonomies SISD SIMD MISD MIMD Each has it’s purpose 04/04/2007

SISD Single Instruction Single Data – sequential (unless you consider the micro-code level) Pentium (of old) VAX SGI Your stereo-typical Von Neumann machines Controller PE Fetch/Decode/Execute 04/04/2007

SIMD Single Instruction Multiple Data – data level parallelism All PEs do the same operations synchronously on their own separate data Connection Machine CM-1, CM-2 IUA CAAPP level Vector processor within SISD machines such as the Cray Fetch/Decode Controller PE Execute 04/04/2007

MISD Multiple Instruction Single Data – dataflow parallelism Systolic array Pipeline machines Not talked about all that much Controller PE Fetch/Decode/Execute 04/04/2007

MIMD Multiple Instruction Multiple Data – control/process level parallelism Cosmic Cube Connection Machine CM-5 IUA ICAP level Controller PE Fetch/Decode/Execute 04/04/2007

SPMD Single Program Multiple Data – data and control level parallelism Can be sub-classed from either SIMD or MIMD PEs have identical programs but separate program counters (asynchronous SIMD) Fetch Controller PE Decode/Execute 04/04/2007

Interesting Bits Claims that SIMD is of “limited application” I think this is unfair but maybe closer to the truth than what Thinking Machines, Inc. was pushing “networking commodity workstations through a local area network” as a MIMD architecture SETI started in 1984 which was prior to publication – I imagine he did not have such a statement in the 1972 paper “However, we cannot expect that the ease of programming these improved configurations will advance” … “few of which are foreseeable.” He speaks from experience and common sense 04/04/2007

End Notes Four basic parallel computer taxonomies SISD SIMD MISD MIMD Each has it’s purpose If someone builds/sells only 1 type, they will try to convince you that you don’t need the rest, no matter which type they build/sell 04/04/2007