
History of the ISA: Digital Equipment Corporation - rbanffy
https://www.allaboutcircuits.com/news/history-of-the-isa-digital-equipment-corporation/
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gumby
This article really barely touches on the issue, even with regard to earlier
influential architectures by DEC alone (plenty of others contributed as well,
though in this regard the most influential were DEC, Intel and IBM in no
particular order). It also ignores Gordon Bell, possibly the inventor of the
ISA as an idea with his profound design choices in the early DEC
architectures.

The most important machines to DEC were PDP-1->PDP-6->PDP-10->DEc-20", PDP8,
and PDP-11->VAX, and from an ISA perspective the -10 and -11/Vax sequences had
pervasive influence until today.

The 36-bit PDP6 architecture (unfairly called a "dead end" by another poster
on this discussion) was highly influential: it was highly orthogonal and what
we would consider today almost RISC, but was easy to program in both assembly
and with a compiler. This is the architecture that gave us the Internet, Lisp
machines, the bitblt instruction (ever used a bitmapped display?) and other
technologies that led to today. The PDP-11 gave us C[+] -- there's a little
PDP-11-like machine in every C and C++ compiler, and pretty much every other
CPU-targeting compiler these days, and as a result, almost every modern ISA
looks like a PDP-11 if you squint a little.

(The article also ignores what a barn burner Alpha was. Its biggest misfortune
was to be born at the wrong time into a family that had fallen on hard times).

~~~
payne92
>The article also ignores what a barn burner Alpha was.

Indeed. 300mhz, dual-issue...in ~1991! Of course, that was before low-power
was "cool" and the first chips were very nice space heaters.

Source: worked on the Alpha team before it was "Alpha" ("EVAX").

~~~
rasz
dont you mean 150MHz in 1992-3?

~~~
payne92
Ah, you are right. 300 “mips” (peak), 150mhz.

The cryo guys had something faster running in the back lab, but I don’t think
they got 2x.

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kabdib
Nothing about the PDP-11 (direct ancestor of the VAX, which the article starts
with). No details of how one ISA influenced another. I guess we can forgive
the relative dead-end of the PDP-8 and PDP-10 architectures.

Good picture of Ken Olsen, though :-)

(I'd forgotten about PRISM, which was canceled through some nasty politics and
caused Dave Cutler to move to Microsoft -- and Cutler's Windows NT was a heavy
contributor to DEC's failure).

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mpweiher
Hmm...is that one article in a series on ISAs, with this article the one on
DEC. Or is it an article on ISAs, using DEC as the example?

The thing is, I can't find an article on IBM's 360, and while I like DEC's
ISAs, the 360 is really the seminal example.

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bogomipz
The article states:

>"VAX was a 32-bit Complex-Instruction-Set-Computer (CISC) ISA designed for
DEC’s VMS operating system."

Is it unique that they designed the ISA for OS? Was this common back then? It
seems the norm for some time now been to write an OS that targets an ISA and
then possibly port it to other ISAs.

EDIT I guess its easy to forget that virtual memory was new and so you needed
to design an architecture that had the concept of paging before you could have
virtual memory support in your OS(VMS)

~~~
davidgould
The VAX and VMS were designed for each other. Many features in the VAX were
created specifically to support VMS. That said, just as the PDP-11 was the
parent of the VAX, the RSX-11 operating system was the parent of VMS.

BTW, the original article is annoying unsubstantial.

~~~
bogomipz
Thanks.

I agree that the original article here is annoying and unsubstantial. Might
you have some better references or links on the the history of VAX/VMS
development and some of the lineage you mentioned such as the RSX-11? Cheers.

~~~
davidgould
Search for a copy of "VAX VMS Internals and Data Structures". I have the
version 4.4 book, but it appears later editions are available at Amazon and
online as pdf. This is pretty dense reading and really goes into detail on the
design and rationale for the design. I'd say it's a whole CS education in one
volume. DEC had some pretty clever people and it shows in this book.

You might find some more historical information at
[https://williambader.com/museum/vax/vaxhistory.html](https://williambader.com/museum/vax/vaxhistory.html)
for VMS or for RSX-11 and PDP-11 here
[https://williambader.com/museum/vax/pdphistory.html](https://williambader.com/museum/vax/pdphistory.html).
Wikipedia has a good article on RSX-11 too.

Apparently you can even legally run RSX-11M on a simulator. Check
[http://simh.trailing-edge.com/](http://simh.trailing-edge.com/) and
[http://rsx11m.com/](http://rsx11m.com/).

I loved PDP-11s, particularly to write assembly, they were elegant. But it was
always a struggle to fit a larger application into a 16 bit address space.

I'd be tempted to try the simulator, but my current hobby computing is doing
embedded firmaware on the STM8 which satisfies my desire to puzzle solve
fitting a lot of function into too small resources.

~~~
bogomipz
Thank you these are great links, I appreciate it. Cheers.

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kbob
This article is fluff. If you're looking for substantive information on the
earlier half of DEC's history, I recommend this book.

Computer Engineering: a DEC View of Hardware Systems Design C. Gordon Bell, J.
Craig Mudge, John E. McNamara

[http://www.computerhistory.org/collections/catalog/102630383](http://www.computerhistory.org/collections/catalog/102630383)

