300 Mbps and faster for a backplane bus. When connecting 4-5 CPUs the bus becomes overloaded and performance drops drastically. If cache is large the hit rate will be high, bus traffic will drop dramatically, allowing many more CPUs to be added. Snoops' on the bus. Used to build a multiprocessor with more than 64 processors.
Processors can access memory simultaneously.
If two CPUs try to access the same memory simultaneously, one of them will have to wait. With n CPUs and n memories, n x n crosspoint switches are needed. The switches can be set in nanoseconds or less. Multicomputers also are configured in a bus or switch type configuration. Each CPU has direct connection to its own local memory.