Optical versus Electronic Bus for Address-Transactions in Future SMP Architectures

The fast evolution of processor performance necessitates a permanent evolution of all the multi-processor components, even for small to medium-scale symmetric multiprocessors (SMP) build around shared busses. This kind of multiprocessor is especially attractive because the problem of data coherency in caches can be solved by a class of snooping protocols specific to these shared-bus architecture. But the bandwidth demand, especially for the addresses, is becoming so important that a technological step must be considered. Optical communications are becoming mature, and bring a huge information bandwidth through the implementation of optical busses. This paper is focused on the address bandwidth needed by shared-bus SMP without suggesting a complete solution. We show that an optical address bus can fulfill the bandwidth demand of future SMPs contrarily to standard electronic busses.