IBM Advanced Computer Systems project: Difference between revisions

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Amdahl's continued arguments for 360 compatibility placed him increasingly at odds with Bertram, who was now running the project. Bertram responded by "quarantining" him and making sure that no one was allowed to talk to him. Around the same time, another ASC team member, circuit designer John Earle, was being moved from the main team due to his working style which was causing friction in the team. Bertram assigned Earle to Amdahl, as a form of punishment. This backfired badly, as Amdahl was able to convince Earle that a 360-compatible version was possible, and Earle went ahead and designed it. The result was the Amdahl-Earle Computer, or AEC/360. Using many of the concepts in ASC-1 they produced a design that was slightly slower than it, but cost perhaps 75% as much to build, with only 90,000 gates instead of 270,000 (a gate requires about five transistors using the ECL logic of the era). Much of the reduction was due to the fewer and smaller registers, which accounted for half of the gates in the ASC-1. The loss of performance due to fewer registers was to be made up by a faster 8 nanosecond clock, possible due to a streamlined internal design.{{sfn|Smotherman|2016|p=63}}

In December 1967, Amdahl began calling people within IBM to tell them about the new design. This proved interesting to management, who arranged a complete project review in March 1968 under the leadership of Carl Conti from IBM Poughkeepsie. Amdahl presented performance estimates based on hand-calculated cycle counts. Lynn Conway would later conclude these numbers were unlikely to be anything close to correct, but the team accepted them in any event.<ref>{{cite web sfn|url=http://ai.eecs.umich.edu/people/conway/Memoirs/ACS/Lynn_Conway_ACS_Reminiscences.pdf |title=IBM-ACS: Reminiscences and Lessons Learned From a 1960’s Supercomputer Project |first=Lynn |last=Conway |date=2011}}</ref> Likewise, Amdahl's claim of an 8 nanosecond cycle was accepted although Mark Smotherman suggests it is not realistic. Conti concluded that on integer benchmarks, the AEC/360 would be up to five times as fast as the ASC-1, it would be up to 2.5 times slower on floating-point, and the complex branching system of ASC seemed to offer 10 to 20% at best and could be adapted to the AEC if desired. But a key point was that if the ASC system was so reliant on the compilers for its performance, moving that code to some other machine could result in far different outcomes and that could be considered a disadvantage.{{sfn|Smotherman|2016|p=67}}

The most serious blow to the ASC was the continued success of the S/360. Around this time, [[NASA]] had taken delivery of a 360 Model 95, which IBM described as "the fastest, most powerful computer now in user operation." A final problem was comments by Max Paley supporting Amdahl's concept. In the aftermath of the review, most of the upper management team left, Amdahl was placed in command, and the AEC/360 became the ACS-360. One major change was to introduce [[register renaming]] as part of the out-of-order system.{{sfn|Smotherman|2016|p=67}}