Old RPN w/ discrete components and acoustic memory

[Dave Britten]

The funny thing is that the program memory in the HP 65 is very conceptually similar, except that it's a very long shift register rather than a mechanical/acoustic device. Technically, the 65 doesn't have "RAM" in that regard, since it isn't "random access", and there are no absolute addresses. It just reads/inserts/swaps bits as they pass by the window. (I imagine there's a bit more to it to allow the calculator to do things like inserting and swapping steps for moving the program pointers around, but that's the general idea.)