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From: Clem Cole <clemc@ccc.com>
To: Noel Chiappa <jnc@mercury.lcs.mit.edu>
Cc: tuhs@minnie.tuhs.org
Subject: Re: [TUHS] [tuhs] PDP-11 and early Unix
Date: Mon, 14 Mar 2022 14:00:32 -0400	[thread overview]
Message-ID: <CAC20D2OMk1F9hNFfvEfETa4J_Y54HNLr54v8QPZax+VnA2cdeA@mail.gmail.com> (raw)
In-Reply-To: <20220314165604.4889918C075@mercury.lcs.mit.edu>

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

>
>
> 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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  reply	other threads:[~2022-03-14 18:03 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-14 16:56 Noel Chiappa
2022-03-14 18:00 ` Clem Cole [this message]
2022-03-14 19:03   ` Angelo Papenhoff
  -- strict thread matches above, loose matches on Subject: below --
2022-03-14 20:38 Noel Chiappa
2022-03-14 20:22 Noel Chiappa
2022-03-14 12:58 Nelson H. F. Beebe
2022-03-14 14:59 ` Ron Natalie
2022-03-14 15:13   ` Clem Cole

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