My first computer had an Intel 8080 so when I got a 6502 it seemed so backward. How could you do anything with that? Then when the 68000 came along it was wonderful and put both the others to shame. I never understood why IBM didn't use it. I still have a hard copy of a preprint of the 68K manual dated 1979.
> 68000 was carefully considered. "AN excellent architecture chip, it has
proven to be a worthy competitor to the Intel-based architecture."
there wer four major concerns:
> 1) 16 bit data path would require more bus buffers, therefore a more
expensive system board.
> 2) more memory chips for a minimum configuration.
> 3) while it had a performance advantage, the 68000 was not as memory
efficient.
> 4) Companion and support chips not as well covered as Intel.o
> He also felt the the 68000 didn't have as good software and support tools,
and the similar register model allowed the porting of 8080 tools
to the 8086/8088.
> "In summary the 8088 was selected because it allowed the lowest
cost implementation of an architecture that provided a migration path to a
larger address space and higher performance implementations. Because
it was a unique choice relative to competitive system implementations, IBM
could be viewed as a leader, rather than a follower. It had a feasible
software migration path that allowed access to the large base of existing
8080 software. The 8088 was a comfortable solution for IBM. Was it the
best processor architecture available at the time? Probably not, but history
seems to have been kind to the decision."
I don't remember where I read about it, but I remember reading about that IBM ditched the 68008 (8 data bit bus version, like the 8088) because some problem with it... availability of it, perhaps.
The beauty of the 6502 is page 0, that gets pretty close to having a 256 byte register file. The 6809 one-upped the 6502 in this respect by allowing the 'direct page' to be set anywhere in memory, as long as it is on a 256 byte boundary.
