[COFF] In Memoriam: Jay W. Forrester, happy birthday Gene Amdahl, and LSD

[dave at horsfall.org (Dave Horsfall)]

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