Well, I started coding on an 8 bit machine, 3.5 ~~GHz~~ MHz, up to total 64 kB of memory (static and dynamic together) - but keyword here is "up to", initially it was less than that. I had all the "OS" pretty clearly mapped out in my head, by address no less. My programs did contain sometimes jumps to physical addresses.

So I think I've some idea how the AGC operated.