From mboxrd@z Thu Jan  1 00:00:00 1970
From: dmr@plan9.bell-labs.com (Dennis Ritchie)
Date: Wed, 4 Sep 2002 00:21:40 -0400
Subject: [pups] Unix and PDP11/20 (was PDP9?)
Message-ID: <73e9d00b78a22185b7b9d6b6c5a183b7@plan9.bell-labs.com>

As Billquist, Wilson and others pointed out, the first
versions of Unix did run on machines with no memory
mapping or protection, and indeed context-switching
was accomplished by swapping.  By 1973 we had the luxurious
11/45, to considerable relief.

I'm not positive about the logo on our first PDP-11.
On the earliest handbook I have, the front panel photo
just shows "PDP11", though inside the handbook
it does talk about the two models (11/10 and 11/20).
Both had the same KA11 processor, but the basic
11/10 sported 1024Kw ROM memory plus a generous
128 words of RAM, while the 11-20 had
4096Kw core RAM, and the ASR33 Teletype was included.
You could add more RAM to the 11/20.

Incidentally, the machine's handbook was a wonder.
In 104 pages (each 5.25x8 inches), it described the whole
system: not only the instruction set but the theory
of the Unibus (including some logic diagrams) together with
programming specifications for the TTY, the clock,
and the paper tape reader.

	Dennis