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Summary

• Barrier synchronization is a good thing
  • Establishes global time
  • Creates a globally coherent state
  • Allows N-way interactions (e.g., voting, multicast) to test properties of the global state
  • Facilitates run-time static scheduling
• Barrier synchronization is easy to implement
  • 4 PE TTL_PAPERS unit uses just 8 TTL chips
  • See http://garage.ecn.purdue.edu/~papers
• Building "parallel computers" that cannot directly access a global state doesn't make sense