Very simplistically, the UNIX operating system is a program that manages and controls computer resources and peripheral resources for users. The UNIX operating system was originally written at the Bell Laboratories in the United States. Today there are various `flavours' of UNIX supplied by different vendors. The `flavour' of UNIX on the School's machines is GNU-Linux. Although each `flavour' is slightly different from the other, and you have used more than one, their differences should be transparent (you should not notice any differences) to you as a user.