RE: 8 bits preference?

To over simplify: Early computers were all over the map. Most Univac, DEC and Control Data machines had 6 bit characters and were typically 12, 36, or 60 bit word lengths. IBM used 6-bit EBCDIC. Human readable representation was octal. Teletypes still used 5-bit Baudot.

IBM changed the game with the System/360. IBM introduced 8-bit ASCII in the mid 60's, it having been developed by ANSI x3.2, first published in 1963. It was a superset of 5-bit Baudot and 7-bit ISO 646.See http://en.wikipedia.org/wiki/ASCII Part of the reason was to equally support accented Latin characters used in European languages. Today it is known as ISO 8859/1.

Since the communications channel width was 8 bits, it made since to organize the computer memory into 8-bit bytes. The System/360 and revolutionary DEC PDP-11 set the new 8-bit multiple standard. The stack oriented PDP-11 led to the single chip microprocessors. Today's Microprocessor are 8, 16, 32 or 64 bits wide. For scientific computing, 64 bits is lovely!

Clive P. Hohberger, PhD
Consultant to
Zebra Technologies Corporation
333 Corporate Woods Parkway
Vernon Hills, IL 60061-3109 USA

-----Original Message-----
From: unicode-bounce_at_unicode.org [mailto:unicode-bounce_at_unicode.org] On Behalf Of Doug Ewell
Sent: Monday, June 27, 2011 2:01 PM
To: unicode_at_unicode.org
Subject: RE: 8 bits preference?

<anbu at peoplestring dot com> wrote:

> Why are codes preferred in multiples of 8?

Because computers read, process, and write information 8 bits at a time
(or 8 times some power of 2).

To read, say, 3 bits, a computer must read in one or two 8-bit bytes,
depending on context, and rotate and mask the unwanted bits. This is
inefficient and makes random-access tasks like searching much more
difficult than if code units are aligned on 8-bit boundaries.

This sort of thing is useful when data size is at a premium, but once
you go there, there are many general-purpose compression techniques that
will provide better efficiency than a straight variable-width encoding.

--
Doug Ewell | Thornton, Colorado, USA | RFC 5645, 4645, UTN #14
www.ewellic.org | www.facebook.com/doug.ewell | @DougEwell ­
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