Photoelectric readers! Yes, that is probably the reason.
(I knew there had to be a reason)

Thanks, 

Duncan 
K2OEQ 



Sent from my Kleinschmidt TT-4/TG, the US Army's first portable digital communications device, 1950-1980




-------- Original message --------
From: "Jones, Douglas W" <[email protected]>
Date: 6/4/25 22:07 (GMT-05:00)
To: Duncan Brown <[email protected]>, Daniel Jones <[email protected]>
Cc: Green Keys <[email protected]>
Subject: Re: M28 reperfs

From: Duncan Brown <[email protected]> -- Wednesday, June 4, 2025 8:45 PM

> What is strange (to me) is that they started out chadless and then went to full perf ...
> Does this imply a problem with the chadless tape?

I am only guessing, but the high-speed photoelectric paper-tape readers that were commonly used with computers starting in the 1960s were really bad at reading chadless tape.  Any time you had a TTY punching tape that was then read by a computer, you probably wanted full-perf tape.

I have or have had several photoelectric readers from the 1960s and 1970s.  None could read chadless tape.  The ones made in the 1970s tended to mechanically trivial, just a stepping motor directly driving the feed sprocket, a tape guide and LED/phototransistor read head.  Way simpler (and cheaper) than Teletype's complex mechanisms that pushed sensing fingers up through the holes in the tape.

              Doug