[TUHS] Teletypes used for early Unix

[Theodore Ts'o]

On Wed, Jul 30, 2025 at 04:12:51PM +1000, Serge Burjak wrote:
> KSR 33 did NOT have a paper tape reader/punch. The Paper Tape punch and
> reader were on the ASR33 model exclusively.

KSR == Keyboard Send and Receive
ASR == Automatic Send and Receive

The paper tape is much like the paper roll used for player pianos,
where the paper roll "automatically" plays the piano without a human
at the keyboard.  The concept predates the computer era by quite some time.

> The paper tape reader was used to bootstrap the OS to most minicomputers of
> the era. There was a limit as to how much paper tape could be fed by the
> internal feed mechanism and would often fail with a CRC check for larger
> punched tape rolls. The reader and punch could be controlled by a key
> sequence sent from the computer. Tape also ran at 110 Baud.

The PDP-8 RIM bootstrap loader:

7756 <Load PC>
6014 <deposit>
6011 <deposit>
5357 <deposit>
6016 <deposit>
7106 <deposit>
7006 <deposit>
7520 <deposit>
5357 <deposit>
7006 <deposit>
6011 <deposit>
5367 <deposit>
6016 <deposit>
7420 <deposit>
3776 <deposit>
3376 <deposit>
5357 <deposit>
0000 <deposit>
0000 <deposit>

<Load paper tape containing the BIN loader into ASR-35 teletype>

7756 <Load PC> <Run>

I got *really* good at toggling in the binary RIM loader into a
PDP-8/i.  (I still have it mostly memorized after all of these
decades.)  The RIM loader was less efficient (it used two characters
for each 12-bit word), and had no checksums.  This could be used to
load the more sophisticated BIN loader that would use the full paper
width and with checksums, and which could read from the high-speed
paper tape reader, if you had that peripheral....

      	   	      	      	   - Ted