octal was also a good fit for a lot of the other dec systems of the time, notably the 8 and the 10. I actually found octal to be a pain in the neck on the -11: values and addresses were 377, or 177777 and 377777 and ... bleah. I was glad when hex came along.

On Mon, Jan 16, 2017 at 1:04 PM Lars Brinkhoff <lars@nocrew.org> wrote:

Warren Toomey wrote:
> I understand why other DEC architectures (e.g. PDP-7) were octal: 18b
> is a multiple of 3. But PDP-11 is 16b, multiple of 4. After all, Unix
> had its own assembler, so was there a need/reason to use octal?

Octal is a natural fit for the instruction set encoding.