From: tkoenig@netcologne.de   
      
   Dan Cross  schrieb:   
   > In article <106uqki$36gll$4@dont-email.me>,   
   > Thomas Koenig   wrote:   
   >>Dan Cross  schrieb:   
   >>> In article <44okQ.831008$QtA1.573001@fx16.iad>,   
   >>> Scott Lurndal  wrote:   
   >>>>[snip]   
   >>>>We tend to be spoiled by modern process densities.   The   
   >>>>VAX 11/780 was built using SSI logic chips, thus board   
   >>>>space and backplane wiring were significant constraints   
   >>>>on the logic designs of the era.   
   >>>   
   >>> Indeed.  I find this speculation about the VAX, kind of odd: the   
   >>> existence of the 801 as a research project being used as an   
   >>> existence proof to justify assertions that a pipelined RISC   
   >>> design would have been "better" don't really hold up, when we   
   >>> consider that the comparison is to a processor designed for   
   >>> commercial applications on a much shorter timeframe.   
   >>   
   >>I disagree.  The 801 was a research project without much time   
   >>pressure, and they simulated the machine (IIRC at the gate level)   
   >>before they ever bulit one.  Plus, they developed an excellent   
   >>compiler which implemented graph coloring.   
   >>   
   >>But IBM had zero interest in competition to their own /370 line,   
   >>although the 801 would have brought performance improvements   
   >>over that line.   
   >   
   > I'm not sure what, precisely, you're disagreeing with.   
   >   
   > I'm saying that the line of though that goes, "the 801 existed,   
   > therefore a RISC VAX would have been better than the   
   > architecture DEC ultimately produced" is specious, and the   
   > conclusion does not follow.   
      
   There are a few intermediate steps.   
      
   The 801 demonstrated that a RISC, including caches and pipelining,   
   would have been feasible at the time.  It also demonstrated that   
   somebody had thought of graph coloring algorithms.   
      
   There can also be no doubt that a RISC-type machine would have   
   exhibited the same performance advantages (at least in integer   
   performance) as a RISC vs CISC 10 years later.  The 801 did so   
   vs. the /370, as did the RISC processors vs, for example, the   
   680x0 family of processors (just compare ARM vs. 68000).   
      
   Or look at the performance of the TTL implementation of HP-PA,   
   which used PALs which were not available to the VAX 11/780   
   designers, so it could be clocked a bit higher, but at   
   a multiple of the performance than the VAX.   
      
   So, Anton visiting DEC or me visiting Data General could have   
   brought them a technology which would significantly outperformed   
   the VAX (especially if we brought along the algorithm for graph   
   coloring.  Some people at IBM would have been peeved at having   
   somebody else "develop" this at the same time, but OK.   
      
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