Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!rutgers!sri-unix!sri-spam!ames!oliveb!sun!scherzo!lyang From: lyang%scherzo@Sun.COM (Larry Yang) Newsgroups: comp.unix.wizards,comp.arch Subject: Re: Power-of-2 (Was : *Why* 8-bit bytes?) Message-ID: <23967@sun.uucp> Date: Wed, 22-Jul-87 13:21:54 EDT Article-I.D.: sun.23967 Posted: Wed Jul 22 13:21:54 1987 Date-Received: Fri, 24-Jul-87 05:54:05 EDT References: <142700010@tiger.UUCP> <2792@phri.UUCP> <8315@utzoo.UUCP> <2807@phri.UUCP> Sender: news@sun.uucp Reply-To: lyang@sun.UUCP (Larry Yang) Organization: Sun Microsystems, Mountain View Lines: 21 Xref: mnetor comp.unix.wizards:3362 comp.arch:1661 In article <2807@phri.UUCP> roy@phri.UUCP (Roy Smith) writes: > > Second (sort of the inverse of question #1), why do modern machines >have such a strong trend towards having power-of-2 word and byte lengths? One reason I can think for having power-of-2 sizes is in terms of addressing. If a word = 4 bytes, then I can address a word by masking out the lower 2 bits. If a word were 5 bytes, this would be more difficult. I can fill a 64-byte cache line by masking out the lower 6 bits of the address. And so on. This doesn't explain why a byte size has to be 8 bits, however. Of course, this touches off the issue of word-aligned and double-word aligned, which I don't even *want* to think about... ================================================================================ --Larry Yang [lyang@sun.com,{backbone}!sun!lyang]| A REAL _|> /\ | Sun Microsystems, Inc., Mountain View, CA | signature | | | /-\ |-\ /-\ Hobbes: "Why do we play war and not peace?" | <|_/ \_| \_/\| |_\_| Calvin: "Too few role models." | _/ _/