from: http://en.wikipedia.org/wiki/RSTS/E "Mentec would later publicly grant a no-cost license to anyone for non-commercial hobby purpose use of the operating system software developed for the PDP-11, and as the result of the release (for non-commercial use) of a PDP-11 emulator for the IBM-PC, as well as image copies of disk drives of RSTS which exist on the Internet, it is possible for a hobbyist to run RSTS/E on a personal computer in software emulation as fast or faster than it originally ran on the real hardware." It's on the web, so it must be true!