From mboxrd@z Thu Jan 1 00:00:00 1970 From: peter at rulingia.com (Peter Jeremy) Date: Sat, 16 Nov 2019 18:23:54 +1100 Subject: [COFF] In Memoriam: Jay W. Forrester, happy birthday Gene Amdahl, and LSD In-Reply-To: References: <99f46273-e2a4-4a82-f827-8c00fb48f633@kilonet.net> Message-ID: <20191116072354.GA74610@server.rulingia.com> On 2019-Nov-16 09:42:47 +1100, Dave Horsfall wrote: >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... 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 -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 963 bytes Desc: not available URL: