Why OpenMP

• Parallel programming landscape before OpenMP
  • Standard way to program distributed memory computers (MPI and PVM)
  • No standard API for shared memory programming
• Several vendors had directive based API for shared memory programming
  • Silicon Graphics, Cray Research, Kuck & Associates, DEC
  • All different, vendor proprietary, similar but different spellings
  • Most were targeted at loop level parallelism
• Commercial users, high end software vendors have big investment in existing code
• End result: users who want portability forced to program shared memory machines using MPI
  • Library based, good performance and scalability
  • sacrifice the built in shared memory advantages of hardware
  • Requires major effort
    • Entire program needs to be rewritten
    • New features needs to be curtailed during conversion

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