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From: news@ism780c.isc.com (News system)
Newsgroups: comp.arch
Subject: Re: Is handling off-alignment important?
Message-ID: <46171@ism780c.isc.com>
Date: 9 Aug 90 18:44:40 GMT
References: <104037@convex.convex.com> <8840014@hpfcso.HP.COM> <2357@crdos1.crd.ge.COM> <25900@mimsy.umd.edu> <2392@crdos1.crd.ge.COM> <MCGRATH.90Aug7220232@homer.Berkeley.EDU> <1990Aug8.212255.3555@zoo.toronto.edu>
Reply-To: marv@ism780.UUCP (Marvin Rubenstein)
Organization: Interactive Systems Corp., Santa Monica CA
Lines: 15

In article <1990Aug8.212255.3555@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
>In article <MCGRATH.90Aug7220232@homer.Berkeley.EDU> mcgrath@homer.Berkeley.EDU (Roland McGrath) writes:
>>On machines that "don't handle misaligned accesses", what do they do when one
>>happens anyway?...
>
>Mostly they trap.  There are probably one or two design groups that were
>foolish enough to just ignore the low bits.

There was at least one design group (an SEL machine) that noticed that they
could encode the operand width using the low order address bits.  In this
way they were able to save a bit in the instruction thus providing an
additional address bit.  Of course, there was no such concept as misaligned
access reference using this scheme.

    Marv Rubinstein