[ih] bytes [Re: "network unix"]

[johnl at iecc.com (John Levine)]

>    > I think the question was really settled in April 1964 when the IBM 360
>    > was announced.
>
>I too was going to mention the 360. I'm not sure we can elucidate _precisely_
>what led to the focus on 8-bit bytes, so questions like 'would the 360 _on
>its own_ have done it' may be forever unknowable. But I do think the 360 was
>one of the biggest factors.

Well, yeah.  In the 1970s I think IBM was still as big as all the other
computer makers combined.

>The other one I'd point to is ASCII. Technically, one only needs 7 bits for
>ASCII, but 7 is odd (although there's no particular reason one couldn't have
>odd-length bytes, but it just feels, well, odd), and so I think ASCII was a
>big driver to 8-bit bytes; it certainly knocked out 6-bit bytes.

So say Amdahl et al in their article on the design of S/360.

https://pdfs.semanticscholar.org/3b9b/2cc9c0ce79aa3995a9b65f4a05c57bcb4efc.pdf

By 1970 it was obvious that the 360's approach of byte addressed words
worked a lot better than the various byte addressing kludges on the 36
bit mainfames (ILDB et al on the PDP-6/10 and some amazingly complex
address modes on the GE 635.)  If you're going to do that, making the
size a power of 2 rather than a multiple of 6 greatly simplified the
logic.  4 bits was too little, 16 was at the time way too big, so 8
bits it was.

The biggest complaint about the 360's 32 bit words was floating point
precision, but that was at least as much due to the well known design
mistakes in 360 hex floating point as the word size.

>    > I think the byte stabilised at 8 bits in my mind because of the PDP-11,
>    > rapidly followed by the Intel 8080 and Motorola 6800.

In Bell's article on the design of the PDP-11 he just says the the
character size is 8 bits, which suggests that at the time that was
obvious.  He mentions the 360 which probably made the choice of byte
addressing obvious, too.  There was a competing 16 bit word addressed
design by the designer of the PDP-8, which after DEC rejected it
became the DG Nova.  DG did OK but I think it's fair to say that the
PDP-11 and Vax did a lot better than the Nova and the Eclipse.

R's,
John