There actually is no difference when you apply case-sensitivity to UNIX (or Unix). However, you're the first person I've ever heard using the term 'unixoid' although it's common to see people refer to Linux, BSD and others as *nix or UNIX-like over the years that I'd worked in and out of Silicon Valley. Where I was entertained by Copernicus, your posting is just eye-rolling silly. Here, let me help you a little bit with some light reading material: http://en.wikipedia.org/wiki/Unix How can you tell the difference? Well, if you're a coder you MIGHT be able to tell the difference when your code has to differentiate between libraries. If you're a system admin, you MIGHT be able to tell the difference when various devices are referred to differently (i.e. eth0 versus hme, eri, or any number of names depending on the driver). If you're a simple command line user, you might also notice when your commands work very differently in UNIX versus using GNU utilities (i.e. df lacks -h or using 'ps -ef' instead of 'ps aux' and so on). They're similar enough to get used to both--but they're clearly different. Thankfully, the GNU stuff can easily be brought in to replace the pure UNIX stuff in most of these UNIX OS's like Solaris, AIX, IRIX, HPUX, and the various array of actual UNIX OS's that I've had to work with over the years. They're different enough to really KNOW the difference when you try to work with them--especially on a day-to-day basis--but thanks to POSIX and to the GNU, they CAN be similar enough to mitigate those differences pretty easily if you try. BTW: Trivia fact for you to ponder in case you didn't learn this along the way... GNU is an acronym for 'GNU is Not UNIX', thusly making my point EVEN more painfully obvious. Here's their website where they even state as much, JUST in case you questioned my accuracy: http://www.gnu.org/ ...you'll note they call their operating system 'UNIX-like' instead of calling it a UNIX or using that weird 'unixoid' term you made up. heheh.. AT&T purist. You're a funny guy. Eventually, with enough practical experience and knowledge, someday you too will know enough to hold up your own end of a conversation, though. Keep learning, lad!