[ih] byte order, was Octal vs Hex, not Re: Dotted decimal notation

[Bill Ricker]

On Wed, Dec 30, 2020 at 11:20 AM Dave Crocker via Internet-history <
internet-history at elists.isoc.org> wrote:

> On 12/30/2020 7:46 AM, Clem Cole via Internet-history wrote:
> > His two main grad students at CMU were Harold McFarland and Bill
> Strecker,
> > and much of the original work on the PDP-11 was done there.
>
> So 3 people did the work.  No wonder they settled on octal.


:-D

3 people ... At least one of whom had been lead on 18-bit and 36-bit
processors previously.

The competing 16-bit design team (Edson DeCastro et al) likewise came from
a 12-bit processor (PDP-8).

Prior to the PDP-11, the entire DEC product line had wordsize divisible by
3.

Octal was in solidly in DEC's DNA before the PDP-11's 16-bit wordsize might
have hinted at something else.

And as previously noted, having 8 registers and 8 addressing modes made for
nice Octal view.
(The lonely leading bit allowed the smallest opcode to be 4 bits while
maintaining octal alignment for the operands!)

So there was no incentive to switch to Hexadecimal to fit the PDP-11
wordsize, at least not for the machine-language coders who are first-in and
set the culture to follow.
(And yes, Octal is easier mental arithmetic than Hexadecimal.)

Bell Labs' Unix and C brought Octal/Decimal/Hex parity to the PDP-11 (and
Vax11/780 thereafter).
(Whether 'B' on the PDP-7 proto-Unix had Hex constants, I haven't a clue.)
(And IDK if any DEC OS or Language products gave Hex first-class standing
before that?)

To bring things full circle and to DARPA history, Dennis Ritchie lived at
the home a Boston-area Aunt while he was Bell's rep at the
DARPA/MIT/Bell/GE=Honeywell Project MAC and Mike Padlipsky (MAP)'s
officemate there. That said-same Aunt was also a volunteer at TCM
Boston/Marlboro with Gordon Bell and myself !