Path: csiph.com!weretis.net!feeder9.news.weretis.net!panix!.POSTED.spitfire.i.gajendra.net!not-for-mail From: cross@spitfire.i.gajendra.net (Dan Cross) Newsgroups: comp.arch Subject: Re: VAX Date: Sun, 10 Aug 2025 12:06:46 -0000 (UTC) Organization: PANIX Public Access Internet and UNIX, NYC Message-ID: <107a20m$1k7$1@reader1.panix.com> References: <0c857b8347f07f3a0ca61c403d0a8711@www.novabbs.com> <1070cj8$3jivq$1@dont-email.me> <10772v8$pml$1@reader1.panix.com> <107768m$17rul$1@dont-email.me> Injection-Date: Sun, 10 Aug 2025 12:06:46 -0000 (UTC) Injection-Info: reader1.panix.com; posting-host="spitfire.i.gajendra.net:166.84.136.80"; logging-data="1671"; mail-complaints-to="abuse@panix.com" X-Newsreader: trn 4.0-test77 (Sep 1, 2010) Originator: cross@spitfire.i.gajendra.net (Dan Cross) Xref: csiph.com comp.arch:113086 In article <107768m$17rul$1@dont-email.me>, Thomas Koenig wrote: >Dan Cross schrieb: >> [snip] >> If you're just talking about RISC design techniques generically, >> then I dunno, maybe, sure, why not, > >Absolutely. The 801 demonstrated that it was a feasible >development _at the time_. Ok. Sure. >>but that's a LOT of >> speculation with hindsight-colored glasses. > >Graph-colored glasses, for the register allocation, please :-) Heh. :-) >>Furthermore, that >> speculation focuses solely on technology, and ignores the >> business realities that VAX was born into. Maybe you're right, >> maybe you're wrong, we can never _really_ say, but there was a >> lot more that went into the decisions around the VAX design than >> just technology. > >I'm not sure what you mean here. Do you include the ISA design >in "technology" or not? Absolutely. >[...] > >> While it's always fun to speculate about alternate timelines, if >> all you are talking about is a hypothetical that someone at DEC >> could have independently used the same techniques, producing a >> more performance RISC-y VAX with better compilers, then sure, I >> guess, why not. > >Yep, that would have been possible, either as an alternate >VAX or a competitor. > >> But as with all alternate history, this is >> completely unknowable. Sure. >We know it was feasible, we know that there were a large >number of minicomputer companies at the time. We cannot >predict what a succesfull minicomputer implementation with >two or three times the performance of the VAX could have >done. We do know that this was the performance advantage >that Fountainhead from DG aimed for via programmable microcode >(which failed to deliver on time due to complexity), and >we can safely assume that DG would have given DEC a run >for its money if they had system which significantly >outperformed the VAX. My contention is that while it was _feasible_ to build a RISC-style machine for what became the VAX, that by itself is only a part of the puzzle. One must also take into account market and business contexts; perhaps such a machine would have been faster, but I don't think anyone _really_ knew that to be the case in 1975 when design work on the VAX started, and even fewer would have believed it absent a working prototype, which wouldn't arrive with the 801 for several years after the VAX had shipped commercially. Furthermore, Digital would have understood that many customers would have expected to be able to program their new machine in macro assembler. Similarly for other minicomputer companies. >So, "completely unknownable" isn't true, "quite plausible" >would be a more accurate description. Plausiblity is orthogonal to whether a thing is knowable. - Dan C.