Foil 13 Shared-Memory Machines

• Interconnection network shown here is actually for the BBN Butterfly, but C-90 is in the same spirit.
• These machines share data by direct access.
  • Potentially conflicting accesses must be protected by synchronization.
  • Simultaneous access to the same memory bank will cause contention, degrading performance.
  • Some access patterns will collide in the network (or bus), causing contention.
  • Many machines have caches at the processors.
  • All these features make it profitable to have each processor concentrate on one area of memory that others access infrequently.