[TUHS] One's complement (was: reviving a bit of WWB)

[Warner Losh]

On Fri, Sep 25, 2020, 9:22 AM Noel Chiappa <jnc at 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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