Re: architecture, The Design of Design

Michael S <already5chosen@yahoo.com> schrieb:

My impression is that until S/360 there was no such thing as different
by 100% SW compatible models.

I think the important thing was that S/360 was designed and built,
right from the start, as a _series_ of compatible computers, which
were upward- and downward-compatible.  They had the challenge
of designing an architecture where the instructions for the
high-end supercomputers still needed to work (although slowly)
on the low-end bread and butter machines, and what was efficient
on the low-end bread and butter machines should not constrain the
high-end supercomputers.

Most other computer series were built one at a time, with successors
usually extending the previous ones (which IBM also did with the /370,
series).  The VAX may have been another such line - DEC did not release
several models all at once, but they did release the cheaper and slower
11/750 after they had released the 11/780.