Optical Waveguides in General Purpose Parallel Computers

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Davis, Martin H., Jr.
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This thesis examines how optics can be used in general purpose parallel computing systems. Two basic assumptions are made. First, optical waveguide communications technology will continue to mature and become more and more prevalent in smaller and smaller scale environments. Second, electronic computational capabilities will continue to increase for at least the next decade. Thus, this research explores ways in which optical waveguide communications can be combined with traditional electronic computing elements to support general purpose parallel computing. The specific question asked is, "How can the properties of optical waveguides give rise to architectural features useful for general purpose parallel computing?" The answers to this question are developed in the context of a distributed shared memory computing design called OBee. This work defines the OBee design, a specific implementation, based on optical waveguides, of a previously developed, more abstract architecture named Beehive. The basic building block of OBee's physical optical architecture is an Optical Broadcast Ring (OBR). The thesis defines how one or more waveguides (or wavelengths) are arranged in varying topologies; it also defines several different access protocols. Together, a particular combination of topology and access protocol define a given OBR's properties. The OBee design employs a particular (OBR) to define a specific implementation of Beehive's reader initiated cache coherency protocol. The OBee design uses two different OBRs to define two distinct implementations of Beehive's sole synchronization primitive, locks. As improvements to Beehive, OBee adds two more synchronization primitives, barriers and Fetch-and-OP. The OBee design uses two different OBRs to define two distinct implementations of barriers; similarly, it uses two different OBRs to define two distinct implementations of Fetch-and-OP. Analytical evaluations of the performance of the raw architectural primitives are presented which show the primitives can be executed in reasonable amounts of time. The thesis concludes that optical waveguides can provide more than just high speed data transmission since the OBee design demonstrates that command primitives can be directly built form OBRs' properties. Several questions for future research pertinent specifically to OBee and generally to optics in computing are enumerated.
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