Plan 9 is an operating system from AT&T's Bell Labs. It was created by the same group which developed UNIX. Their intent was to design a new operating system that incorporated new developments since UNIX's creation, such as networking and graphical user interfaces.
The kernel is written primarily in C, with a minimum of assembly for greater portability. The user-level applications are mostly in C or the rc shell.
Plan 9 is designed in such a way that the "everything is a file" metaphor extends very well. Network connections can be accessed through /net/tcp, for example, and mouse events are written in plain text to /dev/mouse. Every process has a separate namespace.
Available languages include:
- C (Plan 9 dialect)
- sh (POSIX emulation)
- Assembly (all platforms share the same syntax; less machine-specific)
The creators of Plan 9 took the opportunity to build graphics capabilities into the system from the ground up, unlike UNIX. The most frequently-used "window manager" for Plan 9 is called rio, as seen in this image.
Plan 9 is not POSIX-compliant, although it shares similarities with POSIX systems. The architects decided to create a new operating system without backwards-compatibility baggage, which allowed them greater freedom in implementing whatever they thought was important. There is, however, a POSIX emulation layer which allows compilation of some POSIX programs.