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

On Thu, Sep 24, 2020 at 8:22 PM Warner Losh <imp(a)bsdimp.com> wrote: Don't know about the others, but I'm pretty sure PDP-10 wasn't 1's 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(a)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