Shared Address

• Communication medium
  • From mid 80s shared bus became popular leading to the design of SMPs
  • Pentium Pro Quad was the first commodity SMP
  • Sun Enterprise server provided a highly pipelined wide shared bus for scalability reasons; it also distributed the memory to each processor, but there was no local bus on the boards i.e. the memory was still “symmetric” (must use the shared bus)
  • NUMA or DSM architectures provide a better solution to the scalability problem; the symmetric view is replaced by local and remote memory and each node (containing processor(s) with caches, memory controller and router) gets connected via a scalable network (mesh, ring etc.); Examples include Cray/SGI T3E, SGI Origin 2000, Alpha GS320, Alpha/HP GS1280 etc.

Message Passing

• Very popular for large-scale computing
• The system architecture looks exactly same as DSM, but there is no shared memory
• The user interface is via send/receive calls to the message layer
• The message layer is integrated to the I/O system instead of the memory system
• Send specifies a local data buffer that needs to be transmitted; send also specifies a tag
• A matching receive at dest . node with the same tag reads in the data from kernel space buffer to user memory
• Effectively, provides a memory-to-memory copy