IBM 610 workstation computer 3439

Joe Morris

I don't recall that on a printer (doesn't mean, of course, that it didn't happen), but there was a similar issue with the IBM 407 Accounting Machines. The boxes (hideously expensive) were available in several models which differed in which, and how many, pieces defined in the architecture were actually present, but there was apparently a limited number of actual hardware configurations. If you ordered a model that had such-and-such features (e.g., one digit selector) it might come with two digit selectors but one of them would have its common hub connection disconnected and the wire taped up. It was common practice (especially in educational shops) for the taped-up wires to magically find their way back to the plugboard interface. And then there was the model E8, marketed primarily (AFAIK) to the education industry. It was the lowest-level machine with the fewest (nominal) features, but it also ran at only 100 cpm, compared to the 150 cpm for other models. It didn't do this by changing the speed; that would apparently have been too much of a design change. Instead, it ran at standard speed but skipped every third cycle, so instead of going grumFF grumFF grumFF grumFF (etc) the E8 went grumFF grumFF (silence) grumFF (etc) I never was responsible for an E8 so I don't know how easy it would have been to disable the third-cycle suppression.

All it took was to stick a "punch card" (or a piece of one) into a particular relay that caused the extra cycle to happen. Gerard S.