That's why I qualified it with "exceedingly slow" I would think in most cases a "bare metal" implementation would be quicker (and kernel for most intents is that), but user space is good enough for the vast majority of cases not involving direct bit twiddling in hardware. I know that user space is for simplicity and for safety (memory and security). I'm not a newb :) . I'm a developer, I'm just not a kernel dev (although I have written some very simple linux drivers for fun and to get a feel for it and tweaked existing drivers as well).