Re: Hi! What's a PDP-11? Anyone know?

Subject: Re: Hi! What's a PDP-11? Anyone know?
From: Richard Mateosian <srm -at- C2 -dot- ORG>
Date: Tue, 23 Jan 1996 13:29:23 -0800

>PDP's were a line of mini computers from DEC, on
>which Unix was born. On which C was born. BBN began work on what is now
>called Internet with them.

>In fact calling them "a" line of mini-computers does them a disservice.
>They were *the* line that established mini-computers. No one knew it was
>possible before them. They began the march away from a room full of iron
>and batch processing. They spawned a new paradigm in computers, that of
>"interactive computing."

There's a little selective recall here, old timer. It's like looking back
and saying that the Intel line was "the" line of microprocessors, when in
fact others were quite capable and popular and could just as easily have
wound up where the Intel line is today.

First of all, the "PDP line" was all of DEC's machines -- tied together by
the Programmed Data Processor (PDP) label, but little else. Some of the
machines were similar, but there wasn't much similarity of architecture, or
even scale, between a PDP-8, PDP-10, or PDP-11.

There were plenty of other lines of minicomputers too. The Data General
Novas, the Varian 620 series, and the HP 2100 series were all widely used in
the 1970s, and were about as capable as a PDP-8 or PDP-11. The PDP-11 was
the newest of those architectures and had important features that the others
didn't, but it wasn't substantially better. For example, stack management
was easier with the PDP-11's instruction architecture, but not difficult to
accomplish in software on an HP, Nova or Varian. [Believe me, I know,
because I did substantial amounts of systems programming on all of these

The PDP-11 ultimately evolved into something quite powerful, but so did the
Data General and HP lines. Unix grew up on the DEC machines, but it could
have developed just as easily on the other lines. In fact, its greatest
development occurred in the early 1980s, when it migrated to systems based
on Motorola 68000s and other microprocessors.

So -- great as Gordon Bell and his followers were -- let's not overstate the
relative importance of the PDP line. ...RM

Richard Mateosian President, Berkeley STC
Freelance Technical Writer srm -at- c2 -dot- org Review Editor, IEEE Micro

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