Timesharing systems like Unix(tm) are designed to allow multiple users to contemporaneously invoke multiple processes using the same hardware. In the early days of timesharing, files, processes, and users simply coexisted without any protection, but as a result, systems were very unreliable, and users often lost all of their information due to an error in another user's program. Eventually, operating systems were changed so as to protect users, processes, and files from each other, so that each relates to a virtual computer that is independent of other factors in the environment to a large degree.