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* Re: [TUHS] One's complement (was: reviving a bit of WWB)
@ 2020-09-25 15:21 Noel Chiappa
  2020-09-25 15:30 ` Warner Losh
  0 siblings, 1 reply; 6+ messages in thread
From: Noel Chiappa @ 2020-09-25 15:21 UTC (permalink / raw)
  To: tuhs; +Cc: jnc

    > From: Warner Losh

    > I'm pretty sure PDP-10 wasn't 1's compliment / was 2's compliment..

Just to confirm, I pulled out my PDP-10 Hardware Reference Manual; Vol I - CPU
(EK-10/20-HR-001), and it does indeed say (pg. 1-12): "The fixed-point
arithmetic instructions use 2's complement representations to do binary
arithmetic." Selah.

	     Noel


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [TUHS] One's complement (was: reviving a bit of WWB)
  2020-09-25 15:21 [TUHS] One's complement (was: reviving a bit of WWB) Noel Chiappa
@ 2020-09-25 15:30 ` Warner Losh
  2020-09-25 16:10   ` Ronald Natalie
  0 siblings, 1 reply; 6+ messages in thread
From: Warner Losh @ 2020-09-25 15:30 UTC (permalink / raw)
  To: Noel Chiappa; +Cc: The Eunuchs Hysterical Society

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On Fri, Sep 25, 2020, 9:22 AM Noel Chiappa <jnc@mercury.lcs.mit.edu> wrote:

>     > From: Warner Losh
>
>     > I'm pretty sure PDP-10 wasn't 1's compliment / was 2's compliment..
>
> Just to confirm, I pulled out my PDP-10 Hardware Reference Manual; Vol I -
> CPU
> (EK-10/20-HR-001), and it does indeed say (pg. 1-12): "The fixed-point
> arithmetic instructions use 2's complement representations to do binary
> arithmetic." Selah.
>

Back in school, we had our machine organization course. When we learned
about 1's complement, the professor said "I've used a lot of machines that
had this. You will likely never see one with it. There are no operational
machines on campus with that." It stuck with me. We had a TOPS-20
machine...  the odd turn of phrase was due to a professor that had a board
of unknown origin hanging on the wall that was a rumored to be a CDC or
similar... ah, the mid 80s...

Warner

>

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^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [TUHS] One's complement (was: reviving a bit of WWB)
  2020-09-25 15:30 ` Warner Losh
@ 2020-09-25 16:10   ` Ronald Natalie
  0 siblings, 0 replies; 6+ messages in thread
From: Ronald Natalie @ 2020-09-25 16:10 UTC (permalink / raw)
  To: Warner Losh, Noel Chiappa; +Cc: The Eunuchs Hysterical Society

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The DECSystem20 (and the PDP-10 before) were 36 bit two's complement 
machines.  You had to go back to the PDP-1 if you want one's complement 
in the DEC line.    The CDCs and UNIVACs were the only ones that were 
still kicking around in my era.


>>
>>Just to confirm, I pulled out my PDP-10 Hardware Reference Manual; Vol 
>>I - CPU
>>(EK-10/20-HR-001), and it does indeed say (pg. 1-12): "The fixed-point
>>arithmetic instructions use 2's complement representations to do 
>>binary
>>arithmetic." Selah.
>
>Back in school, we had our machine organization course. When we learned 
>about 1's complement, the professor said "I've used a lot of machines 
>that had this. You will likely never see one with it. There are no 
>operational machines on campus with that."It stuck with me. We had a 
>TOPS-20 machine...  the odd turn of phrase was due to a professor that 
>had a board of unknown origin hanging on the wall that was a rumored to 
>be a CDC or similar... ah, the mid 80s...

Warner

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^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [TUHS] One's complement (was: reviving a bit of WWB)
  2020-09-25  0:22             ` Warner Losh
@ 2020-09-25  1:39               ` John Cowan
  0 siblings, 0 replies; 6+ messages in thread
From: John Cowan @ 2020-09-25  1:39 UTC (permalink / raw)
  To: Warner Losh; +Cc: The Eunuchs Hysterical Society

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On Thu, Sep 24, 2020 at 8:22 PM Warner Losh <imp@bsdimp.com> wrote:

Don't know about the others, but I'm pretty sure PDP-10 wasn't 1's
>> compliment / was 2's compliment..
>
>
Correct.  The PDP-1 (18 bits) was DEC's 1's complement machine.  Its direct
successors the 4/7/9/15 had both 1's and 2's complement arithmetic.  The
12-bit 5/8/12 machines had only 2's complement, but retained the PDP-4
mnemonic TAD (Two's-complement Add).  By the time the 36-bit 6/10/20 line
was designed, it was clear that 1's complement was history, and the
mnemonic was changed to ADD.

(The PDP-3 was a PDP-1 with a 36-bit data path, and only one ever went into
production; the PDP-2 was to be a 24-bit machine, perhaps a compromise
between 6-bit and 8-bit byte systems, but was never even designed.)



John Cowan          http://vrici.lojban.org/~cowan        cowan@ccil.org
I marvel at the creature: so secret and so sly as he is, to come sporting
in the pool before our very window.  Does he think that Men sleep without
watch all night?    --Faramir

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^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [TUHS] One's complement (was: reviving a bit of WWB)
  2020-09-25  0:18           ` [TUHS] One's complement (was: reviving a bit of WWB) Greg 'groggy' Lehey
@ 2020-09-25  0:22             ` Warner Losh
  2020-09-25  1:39               ` John Cowan
  0 siblings, 1 reply; 6+ messages in thread
From: Warner Losh @ 2020-09-25  0:22 UTC (permalink / raw)
  To: Greg 'groggy' Lehey; +Cc: The Eunuchs Hysterical Society

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On Thu, Sep 24, 2020 at 6:20 PM Greg 'groggy' Lehey <grog@lemis.com> wrote:

> On Wednesday, 23 September 2020 at 22:33:38 -0400, Clem Cole wrote:
> > Dave: Seymour used ones complement on the 3000 and 6000 series.
> > Maybe there?   The primary HLLs I used on the CDC boxes were FTN and
> > Pascal, but I would not be surprised if that was were you saw it.
>
> I think most of the bigger pre-IBM 360 machines used one's complement.
> Didn't the PDP-10?  I knew it not only from the CDC 3200 and 3800, but
> primarily from Univac (1108 and 494).  The Univac techies explained to
> me that the primary arithmetic function was subtraction; addition was
> subtracting the complement.  And that worked faster with one's
> complement.
>

Don't know about the others, but I'm pretty sure PDP-10 wasn't 1's
compliment / was 2's compliment..

Warner

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^ permalink raw reply	[flat|nested] 6+ messages in thread

* [TUHS] One's complement (was: reviving a bit of WWB)
  2020-09-24  2:33         ` Clem Cole
@ 2020-09-25  0:18           ` Greg 'groggy' Lehey
  2020-09-25  0:22             ` Warner Losh
  0 siblings, 1 reply; 6+ messages in thread
From: Greg 'groggy' Lehey @ 2020-09-25  0:18 UTC (permalink / raw)
  To: Clem Cole; +Cc: The Eunuchs Hysterical Society

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On Wednesday, 23 September 2020 at 22:33:38 -0400, Clem Cole wrote:
> Dave: Seymour used ones complement on the 3000 and 6000 series.
> Maybe there?   The primary HLLs I used on the CDC boxes were FTN and
> Pascal, but I would not be surprised if that was were you saw it.

I think most of the bigger pre-IBM 360 machines used one's complement.
Didn't the PDP-10?  I knew it not only from the CDC 3200 and 3800, but
primarily from Univac (1108 and 494).  The Univac techies explained to
me that the primary arithmetic function was subtraction; addition was
subtracting the complement.  And that worked faster with one's
complement.

Greg
--
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See complete headers for address and phone numbers.
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^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2020-09-25 16:17 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-09-25 15:21 [TUHS] One's complement (was: reviving a bit of WWB) Noel Chiappa
2020-09-25 15:30 ` Warner Losh
2020-09-25 16:10   ` Ronald Natalie
  -- strict thread matches above, loose matches on Subject: below --
2020-09-19  1:51 [TUHS] reviving a bit of WWB Doug McIlroy
2020-09-20 18:42 ` arnold
2020-09-20 19:28   ` Will Senn
2020-09-20 20:12     ` Steve Nickolas
2020-09-24  2:25       ` Dave Horsfall
2020-09-24  2:33         ` Clem Cole
2020-09-25  0:18           ` [TUHS] One's complement (was: reviving a bit of WWB) Greg 'groggy' Lehey
2020-09-25  0:22             ` Warner Losh
2020-09-25  1:39               ` John Cowan

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