FW: [LINK] Is it Gb or GB?

[Glen Turner]

Roger Clarke wrote:

> My memory is that the word 'byte' arose with the IBM 360 c. 1964, and 
> referred and always has referred specifically to an 8-bit block.

That's not right.  A byte is the smallest unit a CPU can
individually address -- a "bite of data" if you like.

There can be any number of bits in a byte, and even these
days specialist processors can have bytes with 128 or more
bits.

The question of "how many bits should a byte of a general
purpose business/scientific computer have" took a long time
to converge to 8 bits per byte.  Eight was eventually the
preferred number since it was the nearest power of two which
could hold a reasonably sized set of English characters.
But those two criteria were not at all recognisably the
important criteria at the time. [1]

Even the distinction between a "byte" and a "word" took a
long time to develop. Computers designed for scientific
computing often had the byte size the same as the word
size. This wasted a lot of memory, but since the purpose
of the computer wasn't to manipulate characters this
didn't matter.

One of the triumphs of the PDP-11, and later VAX, designs
was that they offered a workable compromise between the
demands of business and scientific computing; and part
of that compromise was to distinguish "bytes" (which contained
mainly characters) from "words" (which contained numbers)
and to have the word as an integral number of bytes.  That
compromise worked so well that it is used on all general
purpose CPUs today.

To avoid confusion RFCs invented the term "octet" to refer
to an 8 bit byte rather than using the term "byte".  That's
a somewhat redundant distinction these days.

We're now stuck with an 8-bit byte. No computer which uses
another size is going to be competitive. It would mean
throwing away all your third-party peripherals and it
would prevent the manufacturer from achieving economies
of scale by using standardised designs like the PCI and
USB busses.  No one is going to pay $400 for a keyboard.

The last manufacturer to try something different was DEC
with the original Alpha AXP. It could only address memory
on word boundaries (but used 8-bit bytes as the addressing
unit). The very next revision of the silicon corrected that
and you could address memory using any address, not just
those on word boundaries.

-- 
  Glen Turner         Tel: (08) 8303 3936 or +61 8 8303 3936
  Australia's Academic & Research Network  www.aarnet.edu.au