Another turnkey application was a ticketing system, whose customers included Arsenal Football Club.
G is a dummy index register whose value is always zero, and hence causes the offsets to be treated as absolute addresses in the zeroth (global) segment.
More complex subroutine calls involve the use of the PREP instruction, which saves the return information in the first bytes of the current memory segment.
This tape, which was stored in a small cardboard box on a shelf near the computer, would be entered from the left of the tape-reader.
The tape-reader was an integral part of the front panel of the computer, and would spill out the tape that it had read, on to the floor, on the right-hand side.
Though having changed little in effect over the decades, editing has changed enormously in feeling: only one line of the program was 'displayed' at a time (physically printing it out on the paper); inserted text was printed below the point in the line where it was being inserted, and the rubout key merely crossed-out the text that was to be deleted; the string-find and string-substitute facilities were very rudimentary; and the teleprinter worked at 110 baud (making an enormous clunking and whirring racket as it did so).
At the end of the edit session, the new version of the source program would be output: both as a typed listing, and as a new punched tape.
The linking-loader program, LINK, could then be called from the keyboard, at the Minisystem's prompt, and the object tape fed through the reader.
Both tapes would eventually need to be wound up, but this tended not to be done immediately, because of the programmer's eagerness at finally being in a position to run the program.