Sign magnitude, one's complement, two's complement

Jon Elson elson at
Sat Aug 22 17:42:14 CDT 2015

On 08/22/2015 04:23 PM, Sean Conner wrote:
>    For my own morbid curiosity, and because it came up on another mailing
> list I'm on [1], what machines commercially avaialble were sign magnitude
> and one's complement?  Every machine I've encountered was two's complement
> (okay, IEEE 754 [2] is a sign magnitude format but I'm talking about integer
> implementations here, not floating point).  I've only found reference to one
> sign magnitude computer (the IBM 7090, release in 1959) and a few one's
> complement machines (mostly the PDP series from DEC).
The LINC (Laboratory INstrument Computer) was one's 
complement, with a 12-bit word.  Several derivative machines 
were the same.  The most confusing, of course, were the 
LINC-8 and PDP-12, which had the PDP-8 instruction set with 
two's complement, and the LINC instruction set, with one's 
complement, all in the SAME machine. SHEESH!


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