On 4/12/19 10:00 PM, Dave Babcock via cctalk wrote: > Chuck, > > The Group Mark key was on later IBM 1620 Model 1 typewriters as well as > the Model 2 Selectrics. > > See: > https://www.dropbox.com/s/p2b1449zr6uqh6p/IBM_1620_Console_Typewriter.png?dl=0 > > > The flagged numeric blank was accidentally left out of the print sample > I made. > > Thanks, > Dave
Thanks for that--I guess the CADETs that I fooled with way back when didn't have the group mark on the typewriter keyboard. Didn't matter much, as I mostly used cards, which allowed for some additional bit patterns (e.g. 821 for a record mark). I could see Dijstra's gripes with the machine--characters that you can only move, not test for or do arithmetic on. Characters that you could read, but not write. One thing that I never tried was to insert numeric blanks, record marks and group marks into the addition table and see what happened. Did you ever try that? Would you simply get an error stop if one of the non-numerics showed up in an addition? Egad, I haven't touched one of the things in something like 50 years and yet I can remember the numeric opcodes for much of it. It's amazing that the machines were as popular as they were. Ah, memories... --Chuck
