After learning more about the PALM processor in the IBM 5100, it has a
similarity to the 6502 in that the first 128 bytes of RAM is a "register
file." All its registers (R0 to R15, across 4 interrupt "layers") occupy
those first addresses. In addition, they are physically on the processor
itself
Interesting discussion, but don't forget software was free until on June 23,
1969, when IBM announced its unbundled offerings! The computer manufacturers
then separately priced their software but at it is what sold the hardware for
some time thereafter.
It was, for quite some time, always
