1. Catagory
   1. SISD - uniprocessor
   2. SIMD - data-level parallelism
   3. MISD - no commercial product
   4. MIMD - thread-level parallelism
      1. Shared-memory
         1. SMP(UMA style)
         2. NUMA
      2. Cluster
         1. commodity clusters
         2. custom clusters(high end)
2. Cache Coherence
   1. coherence, defines what values can be returned by a read
   2. consistency, determines when a written value will be returned by a read
   3. protocols
      1. Snooping(good for UMA)
         1. bus
         2. scalability problem
      2. Directory(good for NUMA)
   4. Performance: coherence misses
   5. Implementing Locks
      1. atomic primitive -> lock in memory
      2. cache coherence + atomic primitive(double check) -> lock in cache
3. Memory Consistency
   1. sequential consistency
      1. speculation
   2. relaxed consistency
      1. relax W→R: total store ordering (processor consistency)
      2. relax W→W: partial store order
      3. relax R→W and R→R: weak ordering, the PowerPC consistency model, and release consistency