Both. Unix Version 1 was written in PDP-11 assembler, for the -11/20; although that was a re-write of an earlier version written in PDP-7 assembler. C was developed from B in good part because the word address model of B (inherited from its ancestor BCPL) wasn't a good match for the PDP-11's byte addressing model. More here: https://www.bell-labs.com/usr/dmr/www/hist.html https://www.bell-labs.com/usr/dmr/www/chist.html I read that the networking code in 2.x uses Supervisor mode (apparently it needed more address space than was available with only kernel, even with split I/D). Noel