Potential HW Coherency Solutions

• Snooping Solution (Snoopy Bus):
  • Send all requests for data to all processors
  • Each processor snoops to see if it have a copy
  • Requires broadcast
  • Works well with bus (natural broadcast medium)
  • Prefered scheme for small scale machines
• Directory-Based Schemes:
  • Keep track of what is being shared in 1 centralized place
• Distributed memory => distributed directory
  • Sends point-to-point requests
  • Scales better than Snooping

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