Parallel Computing Paradigms Shared Memory EXAMPLE: Cray YMP C/J 90 SGI Origin 200/2000 Sun E10000 SMP Intel-based computers (Dell, Unisys) Advantages: Easy to program applications (POSIX threads). Disadvantages: Expensieve hardware and maintenance Memory latency due to shared mem segments and semaphores Performance scales poorly with the number of CPUs Message Passing EXAMPLE: Cray T3E Unix (Linux) clusters Advantages: Cheap and fast hardware: CPU speed doubles every 18 months (Moore's law) Fast network interconnect: Ethernet (1 - 10 GBit/sec), Myranet (2 GBit/sec), Infiniband (10 GBit/sec ) Performance scales well with the number of CPUs Disadvantages: Hard to program applications (MPI)