16 Nov
2019
16 Nov
'19
4:42 a.m.
On Fri, 15 Nov 2019, Arthur Krewat wrote:
How did Amdahl get away with making 360 clones? I
would have thought
that IBM would have crushed his bones into dust.
Clones in the way that they were able to run OS/360; that's about all that
I can remember. Hitachi also came out with a clone, as did no doubt many
other manufacturers; after all, the instruction set was public
knowledge...
I dimly recall that some opcodes had undocumented side-effects, so in
theory (and likely in practice) OS/360 could detect whether it was running
on a clone, and "fail to proceed" (in Rolls Royce terms).
My favourite /360 instruction on our customised system was "SVC 254" which
got you supervisor mode (long story, depending upon the statute of
limitations). The operators and I had a love-hate relationship i.e. they
loved to hate me :-) Soon after I got a job with them i.e. better to keep
me inside the tent than out...
-- Dave