OS/Z

OS/Z is a modern, efficient and scalable Operating System. It is designed to be small, elegant, portable, and capable of handling huge amounts of data in a user-friendly way.

To achieve this, author snooped as much limitation as he could, making it just POSIX-like, but not POSIX-standard. For example, only the storage capacity limits the number of files that can be stored, and only the amount of RAM determines how many competing programs can run at one time. If author failed to drop a limit, he turned it into a boot option so the system could be redesigned without recompilation. Because of this, OS/Z has become a highly scalable system.