Related Clues:
- Ma Bell invention
- System whose support ended in 2019
- Venerable operating system
- Alternative to Linux
- Operating system from Bell Labs
- Operating system invented at Bell Labs
- Linux predecessor / 1995 historical drama ..
- Longtime operating system
- Education centre supported by variable software system
- Bell Labs development of the 1970s
- Computer operating system first developed in the 1960s
- Common operating system for supercomputers, once
- Operating system written in C
- Linux predecessor