[TUHS] [tuhs] PDP-11 and early Unix

Clem Cole clemc at ccc.com
Tue Mar 15 04:00:32 AEST 2022

On Mon, Mar 14, 2022 at 12:59 PM Noel Chiappa <jnc at mercury.lcs.mit.edu>

> Not a bad artcle, but it had a number of minor errors, which I found
> irritating.
> They should have gotten an expert to proof it.
Sure - but usually these are way more bad than good.  Usually way too
much urban legend, so I'm thrilled to see the 11 kept alive.

> And a tip of the hatly hat for getting this:
>   Although the ++ and - operators in C are equivalents of DEC and INC
>   instructions, they were inspired by an addressing mode in the PDP-7.
As I said, the authors seem to have done a little homework, although I was
under the impression ??Ken?? had created them for B independently (which,
of course, was first on the PDP-7).  The ++/-- for increment and decrement
was just a nice notation since they are such a common occurrence in real
code, it's handy to have. But, I did not think the PDP-7 ISA includes
addressing modes in the same manner as the 11.  I'm probably confused, but
I thought PDP-7  is a very simple instruction (and small) with an AC,
Link/Indirection and a PC - it reminded me of the PDP-8 more than anything
else [although, IIRC it could do both 1's complement and 2's - depending
the type of AND instruction].
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