On 2018-05-11, Dennis Lee Bieber <wlfr...@ix.netcom.com> wrote:
> On Fri, 11 May 2018 01:55:58 +0100, bartc <b...@freeuk.com> declaimed the
> following:
>
>>On 11/05/2018 01:25, Marko Rauhamaa wrote:
>>> Chris Angelico <ros...@gmail.com>:
>>>
>>>> Octal makes a lot of sense in the right contexts.
>>>
>>> I think octal is a historical relic from a time when people weren't yet
>>> comfortable with hexadecimal.
>>
>>It's a relic from when machines had word sizes that were multiples of
>>three bits, or were divided up on 3-bit boundaries.
>
> The Intel 8080a was 8-bit bytes, but octal was actually more usable
> when interpreting op-codes. 3-bits encoded the processor registers
> (including the "M"emory access via HL address). A(7), B(0)-C(1),
> D(2)-E(3), H(4)-L(5), M(6): MOV H,E => 143 octal is easier to decode
> than 63 hex
The first 8080-compatible "computer" I owned was a Heathkit terminal
with an 8085 CPU. The firmware listings used "split octal":
0x0000 = 000 000
0xffff = 377 377
IIRC, PDP-11 assembly listings and machine documentation generally
used octal for the same reason: the 16-bit instruction word was
internally divided into a number of 3-bit fields.
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