[pups] Unix and PDP11/20 (was PDP9?)

Dennis Ritchie dmr at plan9.bell-labs.com
Fri Sep 6 16:08:02 AEST 2002

Holden's link,


reinforces my guess that our first -11 probably did
have just "PDP11" on the bezel.  The one in my photo
(which has the 20) is doubtless our second -11.
I've looked at this page before, but it slipped my mind.

Our first -11 was very early, and its disk took several
months to arrive: it had TTY33 and high-speed paper tape
as its only peripherals besides the clock.

Early on, for fun, we tried assembling the DEC-supplied
assembler, which came on at least one (maybe more) long
fan-folded paper tapes.  I don't think we ever succeeded; it had to
be fed in twice for the two passes, and enough characters
were dropped that phase errors occurred.

Incidentally, B programs could be run on this first pre-disk
-11, using cross-compilation from GECOS.  There was
a stand-alone predecessor of dc!

BTW, apologies for the units slip in the earlier posting.
Indeed 128 words of RAM on the 11/10, 4096 words
standard on the 11/20 (we splurged with 12K).

Also BTW, the young woman on p. 104 of the first
manual has a just-so-1969 hairdo!  She has her
index finger on one of the console switches, is
holding a Unibus jumper in the other hand, and
the caption is "The PDP-11 provides Direct Device
Addressing...."  The Unibus address pin assignments
that replaced herwere probably more useful, but not
so redolent of history.


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