From: peter at rulingia.com (Peter Jeremy)
Subject: [COFF] In Memoriam: Jay W. Forrester, happy birthday Gene Amdahl, and LSD
Date: Sat, 16 Nov 2019 18:23:54 +1100 [thread overview]
Message-ID: <20191116072354.GA74610@server.rulingia.com> (raw)
In-Reply-To: <alpine.BSF.2.21.9999.1911160930080.408@aneurin.horsfall.org>
On 2019-Nov-16 09:42:47 +1100, Dave Horsfall <dave at horsfall.org> 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: <http://minnie.tuhs.org/pipermail/coff/attachments/20191116/18c1df3c/attachment.sig>
next prev parent reply other threads:[~2019-11-16 7:23 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-15 21:54 dave
2019-11-15 22:26 ` krewat
2019-11-15 22:42 ` dave
2019-11-16 7:23 ` peter [this message]
2019-11-16 16:25 ` clemc
2019-11-17 5:14 ` dave
2019-11-18 16:42 ` clemc
2019-11-18 18:45 ` bakul
2019-11-18 19:19 ` clemc
2019-11-19 20:21 ` peter
2019-11-19 23:17 ` cym224
2019-11-21 19:48 ` dave
2019-11-15 23:19 ` clemc
2019-11-15 23:47 ` krewat
-- strict thread matches above, loose matches on Subject: below --
2018-11-15 22:33 dave
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191116072354.GA74610@server.rulingia.com \
--to=coff@minnie.tuhs.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).