Artifact Details


The IBM ACS System -- A Pioneering Supercomputer Project of the 1960s

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The showcase IBM effort at high-performance computing in the 1960s has traditionally been considered the IBM S/360 Model 91. That machine well deserves the attention it has received. In fact, in the field of computer architecture, the 1960s are known for the CDC 6600 and the IBM Model 91, and many modern processors trace features back to those machines.

However, there was another relatively unknown IBM effort that operated in parallel with the deployment of the Model 91. It was launched by IBM Chairman T. J. Watson, Jr., "to come up with something so much better than the [just announced] 6800 as to once more, in the eyes of the public, put IBM far away in the prestige league."

The project was called. It was set up in California specifically to be located far from normal mainframe development on the East Coast as well as to be close to the Livermore National Laboratories and the advanced work on disk drives at IBM's San Jose facility.

ACS built upon earlier IBM work on Stretch and Stretch-Harvest influenced by the legendary John Cocke, and on IBM's follow-on "Project Y" at the T. J. Watson Research Center. Most of the Project Y personnel moved to California in 1965 to launch ACS. Many other designers and engineers were recruited and one visitor from Livermore Labs commented that he "had not seen such a high concentration of talent since the Manhattan Project."

The ACS architecture incorporated innovations that remain important today, including multiple out-of-order dynamic instruction scheduling, multiple condition codes, a decoupled branch architecture, and instruction pre-fetching. Advanced ECL circuits and optimizing compilers were also crucial parts of the plans for ACS. On reflection it appears to have been the first "superscalar" design, and yet its story remains virtually untold to this day.

In this lecture, former project members describe the exciting atmosphere of the ACS team and the computer design innovations that ACS created. Panel members include: Fran Allen, Lynn Conway, Bill Mooney, Brian Randell, Russ Robelen, and John Zasio. Introduction by Mark Smotherman.

Watch this lecture on CHM's YouTube channel:




Allen, Frank, Speaker
Conway, Lynn A., Speaker
Mooney, Bill, Speaker
Randell, Brian, Speaker
Robelen, Russell, Speaker
Zasio, John, Speaker


Computer History Museum

Place of Publication

Mountain View, CA, USA




Low resolution video file




IBM; supercomputer; supercomputing; Advanced Computing Systems (ACS); Livermore National Laboratory; IBM San Jose Laboratory; ECL; Allen, Fran; Conway, Lynn; Mooney, Bill; Randell, Brian; Robelen, Russ; Zasio, John

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