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From: pf@diab.UUCP (Per Fogelstrom)
Newsgroups: comp.arch
Subject: Re: *Why* do modern machines mostly have 8-bit bytes?
Message-ID: <239@diab.UUCP>
Date: Fri, 24-Jul-87 03:45:26 EDT
Article-I.D.: diab.239
Posted: Fri Jul 24 03:45:26 1987
Date-Received: Sat, 25-Jul-87 18:06:37 EDT
References: <142700010@tiger.UUCP> <2792@phri.UUCP> <8315@utzoo.UUCP> <2807@phri.UUCP> <4957@milano.UUCP>
Reply-To: pf@.UUCP (Per Fogelstrom)
Organization: Diab Data AB, Taby, Sweden
Lines: 13
Summary: Use power of two for anything larger than the smallest object.


WHY 8-bit bytes..  The smallest ammount of data modern machines can deal with
is a bit, and to simplify address computation it is best if the next larger
addressable objects size is of any power of two size above. Take for example
the trivial task to compute the address to the n'th element in an array. So
an 8 bit "byte" (eight bits is a byte, aint it) is a power of two size object
that is larger than a bit. (Imagine bit processing with a machine having 12 bit
words. (using mod/div instead of and/shift).)  But, on the other hand take a
graphic engine with 24 bits as the smallest addessable object (8 bits each for
red,green and blue). So all object sizes is "right" in their own context but
for general processing, power of two's are most suitable. (I think.)

per