One of most important operating environments in the computing history is Multics. It influenced many following operating systems, at least in the unixoid world. 15 years after the last versions (in the seventh year since the shutdown of the last Multics site), Bull now opened up the source code of Multics. When you was born in the mid-eighties (thus knowing nothing than operating systems with a gui), you should read the history page of Multicians.