Time-Sharing

The first electronic computers in the 1950s where enormous mainframes that occupied a whole room and to which the programmer had no direct access at all. The vision of interactive computing led to the development of time-sharing systems, where the whole computing power was put at the fingertips of an individual to assist him in his creative work. You can read the history of this vision at The Dream Machine (2001). At the following video (9 Min., about 1964) Robert Fano from MIT explains this vision and demonstrates the CTSS.

Download this video: fano-on-ctss.mp4

Compare here the high ideals of Robert Fano — pushing the mankind forward — with the poor means available to him — the teletype as console. Compare this with todays much more powerful means but our much more near-sighted fanciless dreams.

Time-Sharing Operating Systems

The Time-Sharing initative produced these operating systems: CTSS, Multics, Unix.

Multics (Multiplexed Information and Computing Service) introduced many important innovations such as a hierarchical file system and a flexible command language.

Multics originated the concept that what you type at command level should be the name of a program that you want to call; a whole flock of ideas such as search rules, working directories, the shell, and redirectable I/O accompanied that innovation, and again this set of innovations is found in virtually every operating system that followed. (In CTSS and earlier systems, all commands were owned by the system, which had to be recompiled to add one; you ran your own programs by executing a system command that loaded and ran them.)

[From article Multics Software Features]

Multics was born as a second generation time-sharing system after the successful CTSS. The Compatible Time Sharing System was build on an IBM 7094. Both systems where developed at MIT between 1961 and 1973 lead by Fernando J. Corbató.

The Unix Shell has its origins in the CTSS shell invented by Louis Pouzin. You can read the story about this invention at his own article The Origin of the Shell. From the last paragraph of this article:

Time sharing, as it became popular, is a living organism in which any user, with various degrees of expertise, can create new objects, test them, and make them available to others, without administrative control and hassle. [...]

Unix was created from 1969 on at Bell Labs by Ken Thompson and Dennis Ritchie as a time-sharing system for their personal use, when the Bell Labs dropped out of Multics development. The main design principle was to create a simple and well-thought-out Multics successor.