16 Nov
2019
16 Nov
'19
10:25 p.m.
Btw the way diagnose instruction worked was it used jumps into the
microcode. Very cool. I still have a TILT deck that is a 4 card program
written using mostly 360/67 diagnose instructions.
FYI. The “DAT” (data address translation-aka the vm unit) was a separate
box attached to the side of the CPU which was filled with incandescent
lamps. Also remember that the console bell on the 360 was a large fire
alarm style bell
This program spelled TILT on the lights of the DAT box and sent a bell char
to the console every .5 sec like a large pinball machine. Sadly it was a
standalone program that we could only run at night but very cool none the
less.
Clem
On Sat, Nov 16, 2019 at 2:24 AM Peter Jeremy <peter(a)rulingia.com> wrote:
On 2019-Nov-16 09:42:47 +1100, Dave Horsfall
<dave(a)horsfall.org> wrote:
--
Sent from a handheld expect more typos than usual
On Fri, 15 Nov 2019, Arthur Krewat wrote:
that
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 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...
More than just the instruction set - IBM published a formal description of
the S/360 (in APL in the IBM Systems Journal issue that announced the
S/360). The S/360 was (I believe) the first case where a company announced
a computer architecture (rather than an implementation) and implementations
were expected to precisely comply with the architecture (no more finding
undocumented instructions and side-effects and writing code that depended
on them). This meant that clone makers could build a clone that accurately
emulated a S/360.
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).
AFAIR, the only "implementation defined" instruction was DIAGNOSE, OS/360
could presumably tell what it was running on by checking particular
DIAGNOSE function. (VM/370 was paravirtualised and used DIAGNOSE to
communicate with the hypervisor - CP).
In the early PC era, it was not uncommon for applications to verify they
were running on a genuine IBM PC by looking for the copyright notice in the
BIOS - which clone makers countered by placing a "not" before an equivalent
copyright notice.
--
Peter Jeremy
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