10

I've found a BESM-6 binary of a Pascal program which plots pretty pseudo-random pictures, like this Flying lines

A date is given as the seed for the RNG, in a "horoscope"-like fashion.

After decompiling, it became clear that the commands to the plotter are 6 bit wide and are, in octal:

  • 11 - pen up
  • 12 - pen down
  • 00-07, 30-37 - king-wise movements, knight-wise movements (as dealing with them is in an assembly block, it's not immediately obvious which is which, and what directions they correspond to)

I've produced the picture by replacing the pen movement routine with

if penDown then writeln(dx, dy, ' rlineto') else writeln(dx, dy, ' rmoveto');

and sending the result to GhostScript.

My question is, what plotter was accepting those commands? One likely target would be a Calcomp, probably Calcomp 565

Calcomp 565

but it could be another Calcomp model, or a Benson (those two brands were known to have been used with the BESM-6).

(The date used in the picture is the build date of the program which appears in the binary.)

Update: I've found that it was Calcomp 763 or 765 and a reference page, but I could not find an English-language reference manual for those devices.

5

There is at least some indication that these are Calcomp commands. The Calcomp Software Reference Manual is available at bitsavers.org and covers the 'Direct Commands' sent to the device. On page 5.24 (page 130 in the linked pdf), it shows:

enter image description here

showing that octal 11 and 12 are indeed Pen Up and Pen Down commands.

3
  • Thank you! It also follows that the program was expecting a later model of Calcomp.
    – Leo B.
    Jan 5 at 17:29
  • @LeoB. - at least for Pen Up/Down, it would not surprise me if those particular commands were in place in an earlier version. Might need to dig deeper into the Calcomp manuals on bitsavers to find an earlier model.
    – Jon Custer
    Jan 5 at 18:44
  • On page 138 there is a similar, even simpler, table for Calcomp 836 and a mention that a minimum of 6 pen movement commands are needed for reliable operation. In the program, 32 are used just in case. So it is all very close, but some details are missing.
    – Leo B.
    Jan 5 at 19:44
4

It was Calcomp 763, or its narrow variant Calcomp 765. I've got a scan of a page from "Машинная графика для системы БЭСМ-алгол" ("Computer graphics for the BESM-ALGOL system" by V. V. Kobelev).

Calcomp 763 commands

Apparently the king-wise commands were 20-27, and 01-07 were twice those.

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