Peter Farley asked about why the mixed operand order among (1) The PoP, (2) HLASM, and (3) generated instructions.
I'm afraid I don't know, but I suspect it's due to (a) time -- the basic architecture is over 50 years old, and (b) the great number of processor architects who have designed instructions over that time. (As my grandmother said, "It just growed that way.") I learned recently that STM was not included in the initial instruction set, but was added closer to System/360 availability. As Peter said, maybe others may have insight as well. John Ehrman
