Hmmm; you’re closer to correct than I. Actual details are covered in http://ed-thelen.org/comp-hist/lgp-30-man.html#R3.16 http://ed-thelen.org/comp-hist/lgp-30

Hmmm; you’re closer to correct than I. Actual details are covered in http://ed-thelen.org/comp-hist/lgp-30-man.html#R3.16 http://ed-thelen.org/comp-hist/lgp-30-man.html#R3.16 where it explains that the “R” instruction would store away the address part of what was typically an unconditional branch. So, it was only by convention that this would be kept at $FOO, and that FOO would return by branching to $FOO. A super-smart compiler (they existed) would know the address of the last instruction of each routine, and be able to R into that location directly before calling (actually, just jumping) to $FOO. One other cute thing was that all memory was on a spinning drum, and you could really speed up your program’s execution by placing variables at addresses that were just about to be under the read head when the current operation was being performed. Otherwise, everything had to wait for up to a whole drum rotation. Kind of the original “pipeline stall”.