Huh. Didn't realize that. I guess after all of the (mostly negative) material I've read here about Perl threads I had assumed that they were totally in-process. Then it's possible I was doing something wrong to produce the clunky thread behavior I was seeing (with the timeslices not being distributed very well), or else Windows threads just do that. BTW, Java can be built with what they call "green" threads which are totally in-process but these days the default build uses native threads including NPTL on Linux.