Computer Science and Engineering

Computer Engineering Seminar

Out-of-order processing-History of the IBM System/360 Mode 91

Robert TomasuloIBM and Amdahl Consulting (ret.)

In 1966, IBM announced the System/360 Model 91, the first computer system to feature out-of-order execution–the ability to automatically find concurrency in sequential code. For a time, the Model 91 installed at NASA's Goddard Space Flight Center was "the fastest, most powerful computer in user operation" . Despite the importance of its critical advances, the Model 91 was a marketing failure, and was withdrawn in 1967. In this talk, Robert Tomasulo, the architect of the Model 91's out-of-order floating point execution unit, will discuss the history of the Model 91, why it failed in the marketplace, and why it took IBM nearly 30 years to sell another out-of-order machine.
Robert Tomasulo joined IBM research in 1956 after graduating from Manhattan College. After nearly a decade gaining broad experience in a variety of technical and leadership roles, he transitioned to mainframe development, including the IBM System/360 Model 91 and its successors. Following his 25 year career with IBM, Bob worked on an incubator project at Storage Technology Corp. to develop the first CMOS-based mainframe system; co-founded NetFrame, a mid-80s startup to develop one of the earliest microprocessor-based server systems; and worked as a consultant on processor architecture and microarchitecture for Amdahl Consulting. In 1997, Bob was awarded the ACM Eckert and Mauchly Award, the highest distinction for work in computer architecture, "for the ingenious Tomasulo's algorithm, which enabled out-of-order execution processors to be implemented" .

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