Related Clues:
- Operating system for many Internet servers
- Operating system in many servers
- System used by servers
- Linux forerunner
- Lifetime, e.g
- Greek characters retire operating system
- NBC or ABC
- Chain of television stations
- Early computer operating system
- Common operating system
- What macOS is based on
- Operating system type
- Rail or road system
- Oft-cloned operating system
- Operating system since the '70s