Here's some light reading on this topic: http://homepage.mac.com/gaggan/mosx.html http://www.macnn.com/feature.php?id=10 http://www.daemonnews.org/200011/osx-daemon.html The upshot seems to be that Mach is a microkernel that can be substituted for the standard kernel in the various flavors of BSD. Apple took FreeBSD, dropped in a Mach microkernel, added some NetBSD commands and a few other things, and they named this amalgam Darwin and released it as open source. I have OS X GM if any ISU'ers want to take a look. TVB ====================================================================== Observation attributed to Prof. Robert Wilensky of the University of California at Berkeley: "We've all heard that a million monkeys banging on a million typewriters will eventually reproduce the works of Shakespeare. Now, thanks to the Internet, we know this is not true."