[elsjaako]

In the story it says:

> The new computer had a one-plus-one addressing scheme, in which each machine instruction, in addition to the operation code and the address of the needed operand, had a second address that indicated where, on the revolving drum, the next instruction was located

Is this correct? The manual you have seems to have a diagram with a +1 operation on the "counter register", which loops back down.

All instructions seem to use a memory address, but they use this for doing the instruction thing (adding, subtracting etc).

Maybe I'm just not understanding the format.

[drfuchs]

The RPC-4000 (the "big brother" of the LGP-30) had each instruction specify the next instruction address. I believe this was to allow for optimizing your program such that the next instruction would always be right under a read head on the drum when the processor was ready for it, because if you missed it, it took a whole revolution of the drum to get back to it (kind of like a cache miss).

In any case, it seems that while Mel wrote lots of code for the LGP-30, the actual hack in the story involved code that Mel was porting from LGP-30 to RPC-4000.