Research in Parallel Processing


Behrooz Parhami: 2007/06/19  ||  E-mail:  ||  Problems:

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On June 19, 2007, Professor Parhami's UCSB ECE website moved to a new location. For an up-to-date version of this page, visit it at the new address:

In the following descriptions, selected items from B. Parhami’s list of publications are provided in brackets. 

Defining the Field

In the literal sense of the term, parallel processing (that is, using multiple processors and/or controllers to handle various tasks concurrently) is found in virtually every computer. Research in parallel processing, however, has a somewhat narrower focus: that of multiple processors or computers cooperating to execute a single computational problem with greater speed, throughput, cost-effectiveness, or reliability compared to any uniprocessor [162]. The processors or computers, and their communication mechanisms, can be homogeneous or heterogeneous. Control can be centralized or distributed. The programming model can entail a shared address space or explicit message passing. Memory access can be uniform or nonuniform in latency. Communication between processors can be direct (point-to-point) or indirect (multilevel switched). These variations, and their many possible combinations, are studied from the viewpoint of unifying models or theories, fundamental limits, distinguishing properties, and suitability to specific application domains. Both hardware design/construction issues and software/algorithm aspects are actively pursued.

Areas of Work

Parallel processing, once viewed as an exotic technology, is now a pervasive one. Small shared-memory multiprocessors are sprouting everywhere and large-scale multicomputers built of commodity components have become quite cost-effective. In the domain of massive parallelism, tens of thousands of processors already appear in some systems and multimillion-node supercomputers are being contemplated. With so many processors, optimization of processor design and its various interfaces, scalability of interconnects, and tolerance to processor or link failures are major issues. These problems have received a lot of attention but much remains to be done. Professor Parhami’s work centers on the interface between parallel architectures and algorithms. He studies the problem of algorithm design for general-purpose parallel computers and its “converse”, the provision of architectural features in systems to help improve computational efficiency, economy, and reliability. These take the form of more efficient communication or fault tolerance mechanisms and, at the extreme, the design of algorithm-based special-purpose architectures. Recently, Professor Parhami has also become involved in studying the theoretical foundations of large-scale and hierarchical interconnection networks for parallel processing.

Current Threads

  • Theory of interconnection networks, algebraic structures [191], [208], [211], [215], [225], [227], [229], [dam], [jccs]

  • Theory of interconnection networks, number theory [137], [216], [217], [218], [220], [221], [jcce]

  • Dependable and fault-tolerant parallel processing [192], [202]

  • Multilevel networks for highly parallel systems [132], [141], [210], [222], [224] (see diagram below)

  • Data-driven control of processor arrays [130], [163], [168], [194], [206]

  • Parallel algorithms and complexity [90], [115], [138], [195], [212]

  • Pruned or periodic interconnection networks [131], [151], [160], [169], [209], [211], [212]

  • Search processor design and associative processing [83], [115], [148]

  • Network packageability and VLSI layout [131], [159], [185], [186], [193]

Diagram depicting the Hamiltonicity of a biswapped network, a particular 2-level hierarchical architecture, built of Hamiltonian components (based on joint work with Dr. Wenjun Xiao and others):


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Dr. Behrooz Parhami, Professor

                     Office phone: +1 805 893 3211
E-mail:                 Messages: +1 805 893 3716
Dept. Electrical & Computer Eng.                  Dept. fax: +1 805 893 3262
Univ. of California, Santa Barbara                Office: Room 5155 Eng. I
Santa Barbara, CA 93106-9560 USA                      Deliveries: Room 4155 Eng. I