[TUHS] MicroVAX architecture (was: Linux is on-topic)

[TUHS] MicroVAX architecture (was: Linux is on-topic)

[Paul Winalski]

On 7/19/20, emanuel stiebler <emu@e-bbes.com> wrote:
>
> That's why DEC made also the MicroVAX. I had once a MVII/BA23 in my
> samsonite. Weird look at customs, but worked ;-)
>
By the early 1980s it was apparent that some of the more complicated
VAX instructions weren't worth the space they took up in firmware.
Especially POLY and EMOD, which turned out to be both slower and less
accurate than coding them up as subroutines.  And the PL/I and COBOL
compilers were implementing packed decimal using decimal shadowing.
Chucking out those instructions and doing them by emulation in the OS
freed up enough chip real estate to allow the remaining VAX
architecture to be implemented on a chip.  All the later VAXen
supported only the MicroVAX subset architecture in hardware/firmware.

I don't recall which was the last VAX to support the whole
architecture in hardware/firmware.  Perhaps the VAX 8200/8300
(Scorpio)?  That was a single-board implementation.  It could be
paired with a high-end Evans & Sutherland 3D graphics monitor.  DEC
tried unsuccessfully to use that combination to compete with Apollo in
the workstation market, but it was too little too late.  One reviewer
said that coupling the E&S graphics to the VAX 8200 was like
turbocharging a lawn mower.  Did Unix support that configuration, or
was it VMS-only?

-Paul W.

Re: [TUHS] MicroVAX architecture (was: Linux is on-topic)

[John Cowan]

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On Sun, Jul 19, 2020 at 4:43 PM Paul Winalski <paul.winalski@gmail.com>
wrote:

And the PL/I and COBOL
> compilers were implementing packed decimal using decimal shadowing.
>

What is decimal shadowing?  I see a few references to the term on line, but
no explanations.  Thanks.



John Cowan          http://vrici.lojban.org/~cowan        cowan@ccil.org
There are books that are at once excellent and boring.  Those that at
once leap to the mind are Thoreau's Walden, Emerson's Essays, George
Eliot's Adam Bede, and Landor's Dialogues.  --Somerset Maugham

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