>>> What is " 2's compliment [sic]" ?

>> 2's complement is a way of representing negative numbers. It is just 1's
>> complement + 1, that is all bits changed to the opposite, then add 1.

> 2's complement is used because it is the most 'natural' way of
> representing signed binary numbers on a machine with a bitwise adder.
> The only possible deficiency of 2's complement is that there is one
> more negative number than there are positive numbers.

On the flip side, 1's complement is symmetrical and has the same
number of values on each side of zero.  Downside is that there are
2 representations of zero.  Postive zero has all bits clear;
negative zero has all bits set.

> In fact, out of all the CPU architectures which I have ever seen,
> not one of them used anything other than 2's complement arithmetic.

Then you just don't go back far enough. :-)  I recall some early
machine used 1's complement.  CDC feels right but maybe it was Univac
or RCA or GE; I'm sure someone else will correct me on this.  Anyway,
a manufacturer that's not in business any more).  But all the machines
I've ever worked on were based on 2's complement as well.

                                                Lee Jones