It fitted into 310K of disk space. References and Further Reading A Quarter Century of UNIX by Peter Salus is the book to read for a historical look at Unix, its ethos and its communal spirit. Old newsletters from AUUG, EUUG and Usenix are fascinating. They also have several tutorials and papers, including the 1974 CACM paper. If you can get it, John Lions Commentary on the UNIX OS is a great read.
Many users regard an operating system's user interface as the operating system itself.
This view is increasing as users become GUI-dependent. What made Unix so great was not the user interface. Unix is good because it embodies a set of powerful concepts in a flexible environment. Users could change their user-interface. Programmers had access to a small but sophisticated set of OS APIs.