6 Jan
2019
6 Jan
'19
11:46 a.m.
On Jan 6, 2019, at 2:34 PM, Bob Smith via cctalk
<cctalk at classiccmp.org> wrote:
With the advent of wide spread introduction of 16 bit machines the
definition of a byte as an 8 bit unit was accepted because ASCII
supported character sets for multiple languages, before the 8bit
standard there were 6 bit, 7 bit variations of he character sets.
Gee, what were teletypes, like the model 15, 19, 28, oh yeah 5 level
or 5 bit..with no parity.
I think some of this discussion suffers from not going far enough back in history.
"Byte" was a term used a great deal in the IBM/360 series, where it meant 8
bits. Similarly "halfword" (16 bits). But as was pointed out, mainframes in
that era had lots of different word sizes: 27, 32, 36, 48, 60... Some of them (perhaps
not all) also used the term "byte" to mean something different. In the PDP-10,
it has a well defined meaning: any part of a word, as operated on by the "byte"
instructions -- which the VAX called "bit field instructions". 6 and 9 bit
sizes were common for characters, and "byte" without further detail could have
meant any of those. In the CDC 6000 series, characters were 6 or 12 bits, and either of
those could be "byte".
"Nybble" is as far as I can tell a geek joke term, rather than a widely used
standard term. "Halfword" is 16 bits on IBM 360 and VAX, 18 on PDP-10, and
unused on CDC 6000. Then there are other subdivisions with uncommon terms, like
"parcel" (15 bits, CDC 6000 series, the unit used by the instruction issue
path).
ASCII was originally a 7 bit code. There were other 7 bit codes at that time, like the
many variations of Flexowriter codes; 6 bit codes (found in typesetting systems and
related stuff such as news wire service data feeds), and 5 bit codes (Telex codes, again
in many variations).
paul