Multics

Multics (Multiplexed Information and Computer Services) was an experimental time-sharing operating system developed in the mid-1960s as a joint research project by Massachusetts Institute of Technology (MIT), General Electric (GE), and Bell Labs.

It was designed as a time-sharing system that allowed multiple users to access a mainframe simultaneously.

Multics introduced many innovations, such as the use of a single-level store (virtual memory), hierarchical file system with arbitrarily nested subdirectories, concept of the command interpreter being a regular program, with additional commands provided as separate programs

Despite its ambitious goals and innovations, the Multics project was too big and too complex. The Bell Labs team concluded that the system was unlikely to deliver a functional or performant operating system in the near future.

AT&T Bell Labs withdrew from the Multics project in 1969. This left key researchers, including Ken Thompson and Dennis Ritchie, looking for a new endeavour.