>>1 here.
Actually I'm writing a kernel and I came across it. I've never seen that before and had a hunch it would just stop everything, but I couldn't imagine why anyone would use that.
Yes, I'm writing an OS to help me learn C. Yes, I know they say don't do that. But I'm going to do it and learn a shit-ton more than I would in my classes, or I'll give up in frustration and become an hero.