Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!edcastle!aiai!richard
From: richard@aiai.ed.ac.uk (Richard Tobin)
Newsgroups: comp.arch
Subject: Re: 64 bits--why stop there?
Message-ID: <3259@skye.ed.ac.uk>
Date: 22 Aug 90 13:57:32 GMT
References: <5539@darkstar.ucsc.edu> <13285@yunexus.YorkU.CA> <30728@super.ORG> <9660@ganymede.inmos.co.uk> <224@csinc.UUCP> <1263.26cdaecc@waikato.ac.nz> <6106@vanuata.cs.glasgow.ac.uk> <2437@crdos1.crd.ge.COM>
Reply-To: richard@aiai.UUCP (Richard Tobin)
Organization: AIAI, University of Edinburgh, Scotland
Lines: 18

In article <2437@crdos1.crd.ge.COM> davidsen@crdos1.crd.ge.com (bill davidsen) writes:
>  While we're all talking about 64 bits, where is it writ' that word
>size shall be a power of two bits? Outside of the prevalence of the
>eight bit byte, is there a good technical reason for it?

As you note, the existence of eight bit bytes makes a difference.  A
risc-like machine on which the number of bytes (by which I mean the
smallest addressable unit) in a word was not a power of two would be
very strange.  How big would the pages be?  What would the alignment
restrictions be? ("doubles must start at an address which is a multiple 
of six"?).

-- Richard

-- 
Richard Tobin,                       JANET: R.Tobin@uk.ac.ed             
AI Applications Institute,           ARPA:  R.Tobin%uk.ac.ed@nsfnet-relay.ac.uk
Edinburgh University.                UUCP:  ...!ukc!ed.ac.uk!R.Tobin