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[10092558]
    Liam Proven ([userinfo_v]liam_on_linux) wrote,
    2021-07-07 22:45:00
    Liam Proven
    [userinfo_v]liam_on_linux
    2021-07-07 22:45:00

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  * Location: Prague
  * Mood: ooooooold
  * Music: Gid Coe on 6music

The historical significance of DEC and the PDP-7, -8, -11 & VAX

Earlier today, I saw a link on the ClassicCmp.org mailing list to a
project to re-implement the DEC VAX CPU on an FPGA. It's entitled
"First new vax in ...30 years? "

Someone posted it on Hackernews. One of the comments said, roughly,
that they didn't see the significance and could someone "explain it
like I'm a Computer Science undergrad." This is my attempt to
reply...

Um. Now I feel like I'm 106 instead of "just" 53.

OK, so, basically all modern mass-market OSes of any significance
derive in some way from 2 historical minicomputer families... and
both were from the same company.

Minicomputers are what came after mainframes, before microcomputers.
A microcomputer is a computer whose processor is a microchip: a
single integrated circuit containing the whole processor. Before the
first one was invented in 1974 (IIRC), processors were made from
discrete logic: lots of little silicon chips.

The main distinguishing feature of minicomputers from micros is that
the early micros were single-user: one computer, one terminal, one
user. No multitasking or anything.

Minicomputers appeared in the 1960s and peaked in the 1970s, and cost
just tens to hundreds of thousands of dollars, while mainframes cost
millions and were usually leased. So minicomputers could be afforded
by a company department, not an entire corporation... meaning that
they were shared, by dozens of people. So, unlike the early micros,
minis had multiuser support, multitasking, basic security and so on.

The most significant minicomputer vendor was a company called DEC:
Digital Equipment Corporation. DEC made multiple incompatible lines
of minis, many called PDP-something -- some with 9-bit logic, some
with 12-bit, 18-bit, or 36-bit logic.

One of its early big hits was the 12-bit PDP-8. It ran multiple
incompatible OSes, but one was called OS-8. This OS is long gone but
it was the origin of a command-line interface with commands such as
DIR, TYPE, DEL, REN and so on. It also had a filesystem with 6-letter
names (all in caps) with semi-standardised 3-letter extensions, such
as README.TXT.

This OS and its shell later inspired Digital Research's CP/M OS, the
first industry-standard OS for 8-bit micros. CP/M was going to be the
OS for the IBM PC but IBM got a cheaper deal from Microsoft for what
was essentially a clean-room re-implementation of CP/M, called
MS-DOS.

So DEC's PDP-8 and OS-8 directly inspired the entire PC-compatible
industry, the whole x86 computer industry.

Another DEC mini was the 18-bit PDP-7. Like almost all DEC minis,
this too ran multiple OSes, both from DEC and others.

A 3rd-party OS hacked together as a skunkworks project on a disused
spare PDP-7 at AT&T's research labs was UNIX.

More or less at the same time as the computer industry gradually
standardised on the 8-bit byte, DEC also made 16-bit and 32-bit
machines.

Among the 16-bit machines, the most commercially successful was the
PDP-11. This is the machine that UNIX's creators first ported it to,
and in the process, they rewrote it in a new language called C.

The PDP-11 was a huge success so DEC was under commercial pressure to
make an improved successor model. It did this by extending the 16-bit
PDP-11 instruction set to 32 bits. For this machine, the engineer
behind the most successful PDP-11 OS, called RSX-11, led a small team
that developed a new, pre-emptive multitasking, multiuser OS with
virtual memory, called VMS.

(When it gained a POSIX-compliant mode and TCP/IP, it was renamed
from VAX/VMS to OpenVMS.)

OpenVMS is still around: it was ported to DEC's Alpha, the first
64-bit RISC chip, and later to the Intel Itanium. Now it has been
spun out from HP and is being ported to x86-64.

But the VMS project leader, Dave Cutler, and his team, were
headhunted from DEC by Microsoft.

At this time, IBM and Microsoft had very acrimoniously fallen out
over the failed OS/2 project. IBM kept the x86-32 version OS/2 for
the 386, which it completed and sold as OS/2 2 (and later 2.1, 3, 4
and 4.5. It is still on sale today under the name Blue Lion from Arca
Noae.)

At Microsoft, Cutler and his team got given the very incomplete OS/2
version 3, a planned CPU-independent portable version. Cutler et al
finished this, porting it to the new Intel RISC chip, the i860. This
was codenamed the "N-Ten". The resultant OS was initially called OS/2
NT, later renamed - due to the success of Windows 3 - as Windows NT.
Its design owes as much to DEC VMS as it does to OS/2.

Today, Windows NT is the basis of Windows 10 and 11.

So the PDP-7, PDP-8 and PDP-11 directly influenced the development of
CP/M, MS-DOS, OS/2, Windows 1 through to Windows ME.

A different line of PDPs directly led to UNIX and C.

Meanwhile, the PDP-11's 32-bit successor directly influenced the
design of Windows NT.

When micros grew up and got to be 32-bit computers themselves, and
vendors needed multitasking OSes with multiuser security, they turned
back to 1970s mini OSes.

This project is a FOSS re-implementation of the VAX CPU on an FPGA.
It is at least the 3rd such project but the earlier ones were not
FOSS and have been lost.
Tags: dec, os-8, os/2, pdp, vax, vms
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