Gene Amdahl

American physicist (1922-2015)

Gene Myron Amdahl (November 16, 1922 - November 10, 2015) was an American computer architect and high-tech entrepreneur, chiefly known for his work on mainframe computers at IBM and later his own companies, especially Amdahl Corporation. He formulated Amdahl's law, which states a fundamental limitation of parallel computing.

Gene Amdahl, 2008


  • The term architecture is used here to describe the attributes of a system as seen by the programmer, i.e., the conceptual structure and functional behavior, as distinct from the organization of the data flow and controls, the logical design, and the physical implementation. i. Additional details concerning the architecture,
    • Gene Amdahl, Gerrit Blaauw, and Fred Brooks (1964) "Architecture of the IBM System." in: IBM Journal of Research and Development Vol 8 (2) p. 87-101
  • We tend to think that the phenomenon of engineers and scientists being at the top of a company is something that started with Bill Gates, Steve Wozniak or Gary Kildal. But this just isn’t the case. Even back in the days when IBM was the single most important computer company, it was possible for one of its engineers to escape and make an impact that disturbed even Big Blue.

Validity of the single processor approach... (1967)


Amdahl, Gene M. "Validity of the single processor approach to achieving large scale computing capabilities." Proceedings of the April 18-20, 1967, spring joint computer conference. ACM, 1967. (reprint)

  • For over a decade prophets have voiced the contention that the organization of a single computer has reached its limits and that truly significant advances can be made only by interconnection of a multiplicity of computers in such a manner as to permit cooperative solution. Variously the proper direction has been pointed out as general purpose computers with a generalized interconnection of memories, or as specialized computers with geometrically related memory interconnections and controlled by one or more instruction streams.
    Demonstration is made of the continued validity of the single processor approach and of the weaknesses of the multiple processor approach in terms of application to real problems and their attendant irregularities .
    • p. 483
  • The first characteristic of interest is the fraction of the computational load which is associated with data management housekeeping. This fraction has been very nearly constant for about ten years, and accounts for 40% of the executed instructions in production runs.
    • p. 483
  • Data management housekeeping is not the only problem to plague oversimplified approaches to high speed computation. The physical problems which are of practical interest tend to have rather significant complications. Examples of these complications are as follows: boundaries are likely to be irregular; interiors are likely to be inhomogeneous; computations required may be dependent on the states of the variables at each point; propagation rates of different physical effects may be quite different; the rate of convergence, or convergence at all, may be strongly dependent on sweeping through the array along different axes on succeeding passes; etc. The effect of each of these complications is very severe on any computer organization based on geometrically related processors in a paralleled processing system.
    • p. 483

Quotes about Gene Amdahl

  • At Sandia National Laboratories, we are currently engaged in research involving massively parallel processing. There is considerable skepticism regarding the viability of massive parallelism; the skepticism centers around Amdahl’s law, an argument put forth by Gene Amdahl in 1967 that even when the fraction of serial work in a given problem is small, say, s, the maximum speedup obtainable from even an infinite number of parallel processors is only l/s. We now have timing results for a 1024-processor system that demonstrate that the assumptions underlying Amdahl’s 1967 argument are inappropriate for the current approach to massive ensemble parallelism.
  • Gene Amdahl is a physicist who got into computers because he wanted to work out something complicated. In 1950 he was asked by one of his professors to calculate whether the nuclear strong force was really enough to hold together a nucleus. For thirty days Amdahl slaved over a slide-rule and a mechanical desk calculator to provide only two more significant digits to the solution. This is the sort of experience that drove many a scientist to become a computer pioneer!
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