IBM Advanced Computer Systems project: Difference between revisions

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Amdahl continued to agitate for a 360-compatible version of the machine. In January 1967, [[Ralph L. Palmer]] asked [[John Backus]], [[Robert Creasy]], and Harwood Kolsky to review the project and Amdahl's concept. Kolsky concluded that the 360-compatible version would be too difficult, and pointed out that the ASC was aimed at the [[CDC 6600]] market, not the 360's, so if the customer was interested in compatibility, 6600 compatibility would seem more useful. The next month, Amdahl once again argued for 360 compatibility for marketing reasons.{{sfn|Smotherman|Sussenguth|Robelen|2016|p=63}}

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 removed from the main team due to his working style which was causing friction in the team. Bertram assigned Earle to Amdahl, apparently 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|Sussenguth|Robelen|2016|p=63}}

In December 1967, Amdahl began calling people within IBM to tell them about the new design. Kolsky was sent to meet with Amdahl to get a more detailed description of the proposed design.{{sfn|Conway|2011|p=20}} ThisAround provedthe interestingsame to managementtime, whoAmdahl arrangedbegan acalling completepeople projectwithin reviewIBM into Marchtell 1968them underabout the leadershipnew of Carl Conti from IBM Poughkeepsiedesign. AmdahlAs presentedword performance estimates based on hand-calculated cycle counts. Conti accepted Amdahl's arguments that on integer benchmarks,of the AEC/360concept wouldspread be up to five times as fast asaround the ASC-1,System itDevelopment wouldDivision be up to 2.5 times slower on floating-point(SSD), and the complexdivision's branchingvice systempresident of[[Erich ASCBloch]] seemedbegan to offerorganize 10an tointernal 20%review. atThe bestASC andteam couldresponded be adapted to the AEC if desired. Butwith a key"frantic" point made by Conti wasredesign that ifreduced the ASCnumber systemof wasgates sofrom reliant on the compilers for its performance270, moving that code000 to some200,000 otherwith machinelittle couldeffect resulton inperformance, farwhich differentstrongly outcomessuggested andit that could be considered awas disadvantageoverdesigned.{{sfn|SmothermanConway|Sussenguth|Robelen|20162011|p=6727}}

Bloch selected Carl Conti from IBM Poughkeepsie to handle the review, which occurred in March 1968. Amdahl presented performance estimates based on hand-calculated cycle counts. Conti accepted Amdahl's arguments 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 made by Conti 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|Sussenguth|Robelen|2016|p=67}} He also concluded that the AEC would be closer to 108,000 gates, but that was still almost half that of the ASC.{{sfn|Conway|2011|p=27}}

The most serious blow to the ASC was the continued success of the S/360. In January 1968, [[NASA]] had taken delivery of a 360 Model 95, which IBM described as "the fastest, most powerful computer now in user operation."{{sfn|Smotherman|Sussenguth|Robelen|2016|p=67}} Another problem was that Max Paley publicly supported Amdahl's concept. In May, IBM announced the ASC-1 would be cancelled and the AEC/360, to be known as the ASC-360 from that point, would move forward. Most of the upper management team left, and Amdahl was placed in command. One major change during this period was to introduce [[register renaming]] as part of the out-of-order system and changes to the [[branch prediction]] system.{{sfn|Smotherman|Sussenguth|Robelen|2016|p=67}}

A final "review" was performed in April, but this was brief and seemingly already decided. In May, IBM announced the ASC-1 would be cancelled and the AEC/360, to be known as the ASC-360 from that point, would move forward. Although Amdahl's competition design had much to do with this, it was not the only reason. Amdahl had also argued that the $15 million would better be spent on improving the operating systems on the 360, which would improve the entire lineup, not just the AEC. But perhaps the most serious blow to the ASC was the continued success of the S/360. In January 1968, [[NASA]] had taken delivery of a 360 Model 95, which IBM described as "the fastest, most powerful computer now in user operation."{{sfn|Smotherman|Sussenguth|Robelen|2016|p=67}} Although the ASC would have outperformed the Model 95 by a wide margin, by this time Watson Jr. was considering withdrawing from the supercomputer market entirely.{{sfn|Conway|2011|p=29}}

Many of the retrospective articles on the ASC project note that the original machine would have been a world leader. Conway notes that "In hindsight, it is now recognized that had the ACS-1 been successfully built, it would have been the premier supercomputer of the era."{{sfn|Conway|2011|p=20}} The decision to cancel the original design rested mostly on the cycle counts which had not been tested as the simulator she had developed had not been ported.{{sfn|Conway|2011|p=20}} Likewise, Amdahl's claim of an 8 nanosecond cycle was accepted by the Conti review although Mark Smotherman suggests it is not realistic.{{sfn|Smotherman|Sussenguth|Robelen|2016|p=67}}