CDC 6600 - Why so awesome?

Eric Smith spacewar at
Wed Jun 22 21:26:10 CDT 2016

On Wed, Jun 22, 2016 at 7:45 PM, Swift Griggs <swiftgriggs at> wrote:
> People who
> complain about twos-compliment being a weird hack

Encode negative integers using this one weird trick!

By the way, it's two's complement.  A twos compliment would be
something like, "Hey, nice twos!".  #overlypedantic  :-)

>> ADJBP (ADJust Byte Pointer, which can back up as well as move forward).
> I find that weird, but possibly useful once I figured out how to implement
> it.

It's just pointer arithmetic to add a signed integer to a character
pointer, to move the pointer forward or backward some number of
character positions.

Of course, it can be used on anything represented in a PDP-10 byte,
which can be any number of bits up to 36; it doesn't have to be a
character per se, but character handling is possibly the most common
use of the PDP-10 byte instructions.

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