Talk:DEC PRISM

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The narrative blurs significantly beginning at the third paragraph.

The PRISM specification was developed over a period of many months by a five person team: Dave Cutler, Dave Orbits, Rich Witek, Dileep Bhandarkar, and Wayne Cardoza. Existing RISC architectures influenced this team, as did the Cray instruction set, MIPS not more to my knowledge than any other. This work was 98% done 1985-1986 and was heavily supported by simulations (written and run by Pete Benoit) on a large VAXcluster at DECwest.

The MIPS R3000 came out three years later, in 1988. Sample silicon was likely not available until late 1987, if then. The Advanced Computing Environment consortium was two to three years after that (1990-91?).

DEC struggled throughout the mid-to-late 1980s with how best to respond to RISC, UNIX,and workstations. One group advocated sticking with the VAX, and taking it into mainframe OLTP; others to adopt something standard (and generic) like MIPS for short-term sales, others to develop a proprietary RISC-Y VAX successor, like PRISM or Alpha. The R3000 contingent had their own "next big thing" effort -- when it did not save the company (due largely to DECnet imposed incompatibilities with non-DEC MIPS-based systems) and the VAX 9000 was underwhelming, PRISM morphed into Alpha.

The PRISM team was pulled this way and that throughout 1985 to 1988 by the debate within the company. From one week to another PRISM was ECL or CMOS, 32-bit or 64-bit, a vector-oriented system, a cluster-centric database accelerator, or something else as the factions within the company tried to make it fit into a common world view (as well as existing VAXclusters.)

I believe Dave's frustration with this period at DEC led to his decision to go to Microsoft.

The seriousness of DEC's situation later in the 1980s created the concensus that allowed Alpha to emerge.

 John Coombs
 PRISM Hardware Product Manager
 DECwest / Digital Equipment Corporation 1985-1988

In retrospect I see how the wording is unclear in terms of the "MIPS influence", which seems to be what I was saying. However it does seem that some sort of comparison between PRISM and MIPS is needed, because the two archetechtures are very similar -- and contrast, for instance, with the other well known system of the era, RISC/SPARC.

By the way, does the Alpha Implementations book have GOOD details on the history of PRISM and earlier attempts? I'd love to flesh this article out a lot more, but the book is about $120 so... Maury 23:18, 12 July 2006 (UTC)

Maury, I believe the Alpha Implementation book (we're both referring to Dileep's book right?) offers a good balanced history as well as some good comparisons of Alpha vs. other RISC architectures. Perhaps you could get it through your local library or interlibrary loan? John