IBM Advanced Computing Systems -- Draft Legacy section

Mark Smotherman
last update February 24, 2010

under construction
(This reflects my current understanding. I very much appreciate corrections and new material.)


ACS never made it out of the laboratory; I suppose it was too big and expensive, but for me it was probably the most exciting project I have ever been involved in. In reflecting on this, I believe that what made it particularly exciting was that we were a small team, mostly hand-picked by Jack Bertram, and we pioneered every aspect of the project....

My only regret about ACS is that unlike compiler ideas, we did not take the time to publish our ideas on hardware so others could build on them.

-- John Cocke, Turing Award Lecture (CACM, March 1988)

A partial list of the impact of the ACS efforts would include:

text below needs to be revised

Further work was done at IBM in the 1970s on superscalar S/370s, but few, if any, public documents exist. The exception is the high-end ES/9000 Model 520 processor - a two-issue superscalar, designed during the 1980s and described by John Liptay in the July 1992 issue of the IBM Journal of Research and Development.

[See Robert Tomasulo, "Out-of-order processing - History of the IBM System/360 Model 91" (video, 40:38 in length). At 5:50 and again at 9:50 he describes a multiple-instruction-issue IBM mainframe that was complete in its logical design circa 1972 but not built because of expense.]

In 1989, 20 years after the cancellation of the ACS, IBM introduced the four-way superscalar RS/6000. John Cocke was a key influence on the design. Even today, three decades after the ACS, state-of-the-art superscalar processors are just catching up to the ACS: the DEC 21264 fetches up to four instructions per cycle and can issue up to six per cycle; the IBM POWER3 also fetches up to four instructions per cycle and can execute up to eight per cycle.

Here are some contributions of ACS to IBM in particular and to the field of computer design and engineering in general:

US Patents associated with ACS techniques

IBM Technical Disclosures associated with ACS techniques

Navigation within IBM ACS pages:

Back to first ACS page

Next section: ACS Veterans