character codes, was RE: Really stupid PDP assembler question

From: Tom Jennings <tomj_at_wps.com>
Date: Sun Jun 27 02:36:43 2004

On Sat, 2004-06-26 at 13:10, der Mouse wrote:
> >> "What significant advantage did octal have over hex notation
> >> (especially in the late '60s timeframe)?"
> > I'm a bit skeptical of the printer-hardware answer. Printing
> > calculators don't care about notation, only humans do.
>
> Right. But:
>
> - A power-of-two base is important because it maps trivially to and
> from binary.
> - A base less than ten is important so you can use existing printing
> calculator mechanisms (capable of only 0-9) for output.
>
> That leaves bases 2, 4, and 8. Which one would _you_ pick?

You're extrapolating modern ideas backwards. It doesn't work.

I would like to see some evidence for "existing printer mechanisms"
being the basis for entire notational systems.

2, 4,, 8... is "logical" but that's immaterial -- bi-quinary was used a
lot, 1 2 4 8 representations of BCD were not the only ones used, and
people insisted on decimal internal representations when it's "obvious"
that binary is better.


> Another reason to group bits in threes: three divides six, so character
> boundaries fall on digit boundaries (ie, the question that started this
> thread off would not arise under such a system).

Well yes, 6-bit characters, octal is convenient, was my (unstated)
intent...


I defer to Hans on IBMs history, and he may be right on the 5-bit thing
too (I deleted before I got to reply), but Emike Baudot's code was
manually entered, and variations of the code sure look like they ended
up in ITA2 aka Baudot teleprinter code.
Received on Sun Jun 27 2004 - 02:36:43 BST