I came across this blog post while researching the history of the `roff` family of type-setting systems: the Graphic Systems’ C/A/T phototypesetter was the output device that Joe Ossanna’s troff was written for.

I love the hacker spirit of by-passing the paper tape input that they were supposed to use though I can only begin to imagine the frustration the early Unix developers might have felt when they had to do so much work – only to see a typeset error message.