Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!seismo!husc6!hao!ames!ptsfa!ihnp4!ihlpl!jhh
From: jhh@ihlpl.ATT.COM (Haller)
Newsgroups: comp.unix.wizards
Subject: Re: Size of SysV "block" (really: byte != 8 bits)
Message-ID: <2425@ihlpl.ATT.COM>
Date: Thu, 23-Jul-87 16:42:12 EDT
Article-I.D.: ihlpl.2425
Posted: Thu Jul 23 16:42:12 1987
Date-Received: Sat, 25-Jul-87 11:11:53 EDT
References: <857@bsu-cs.UUCP> <326@hubcap.UUCP>
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 43
Summary: Non-eight bit bytes should die

In article <326@hubcap.UUCP>, beede@hubcap.UUCP (Mike Beede) writes:
> Seriously--different machines serve different purposes, and so are designed
> differently.  That is why it is foolish to freeze some design parameter
> arbitrarily.  I don't see that there is, for instance, a clear argument
> against 36 bit words and 9 bit bytes as opposed to 32 bit words and 8 bit
> bytes, especially if your application works well with 9 bit quantities.

The clear argument against 36 bit words and 9 bit bytes is data
communications.  Like it or not, data communications have virtually
standardized the 8 bit byte.  Just try to generate TCP/IP headers
on a 9 bit machine, packing all of the data contiguously.  Oh,
you want to use a communications processor to do that?  How
many bits is its byte?

Look at some of the higher level ISO protocols, and you will
find that the basic unit of data is, surprise, surprise, an octet.
Oh, sure, there is support for arbitrary bit strings, but
even they are padded to octet boundaries.

Back in the 60's, and possibly up to the mid 70's, when 7 track
mag tape wasn't considered hopelessly obsolete, there was room
for argument on what size provided the best 'byte'.  However,
the de facto standard is an 8 bit byte, which is becoming more
and more institutionalized as time progresses.

Given that a byte is an important measure, byte addressability
becomes important in hardware architectures.  Given that
our machines operate with binary logic, word sizes are going
to be powers of two bytes long, just so that byte addresses
can be easily converted into word addresses, which is typically
related by a power of two to the memory and bus architecture.
Look at the Harris/6 if you want to see what kind of
contortions were necessary to provide byte addressability
with a 24 bit word size.

In summary, I agree that while there was no good technical reason
to have an eight bit byte originally, anyone designing a new
computer that does not have an eight bit byte will be doomed
to market failure.  If Univac's 1100 series had taken off better than
IBM's machines, I would probably be saying that six bit bytes
are the wave of the future.  That is not the case.

John Haller