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

Carl Lowenstein cdl at mpl.ucsd.edu
Sat Sep 7 10:36:52 AEST 2002

> From: Dennis Ritchie <dmr at plan9.bell-labs.com>
> Subject: [pups] Unix and PDP11/20 (was PDP9?)
> Date: Fri, 6 Sep 2002 02:08:02 -0400
> Holden's link,
> http://www.psych.usyd.edu.au/pdp-11/11_20.html
> 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.

I was there once myself.  The problem was fuzzy holes in the DEC-punched
fan-fold paper tape.  So I toggled in a small utility program
"wait, read, wait, punch, loop" to copy from the TTY reader to the
high-speed punch.  The sensing pins of the TTY had no trouble with the
fuzzy holes, and I got paper tapes that worked in the high-speed reader.

    carl lowenstein         marine physical lab     u.c. san diego
                                                 clowenst at ucsd.edu

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