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

[Dave Horsfall]

On Sat, 16 Nov 2019, Peter Jeremy wrote:

> 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.

Ah, I'd forgotten about the APL documentation; thanks!  Talk about giving 
away the keys to the kingdom: Amdahl, Fujitsu, Hitachi...

> 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).

Another point I had forgotten :-(  Yep, the DIAG instruction was utterly 
implementation-dependent, and thus OS/360 could tell whether it was 
running on a clone or not.

Cut me some slack; I turned 67 last month :-(

> 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.

I remember the days of the "grey imports" (or "gray" for the Americans); 
if it ran Flight Simulator and not labelled "IBM" then it was technically 
illegal; shortly afterwards if it did *not* run FS then nobody would buy 
it :-)

How things change...

-- Dave