The OS-9 operating system is a multi-user multi-tasking real-time operating system produced by Microware Systems Corporation that is largely intended for embedded applications. It currently exists in four forms:
One of the best characteristics of OS-9 is its incredibly efficient use of system resources (memory/CPU power) an example of this is that OS-9 Level I can support multiple users on a machine with 64k without resorting to virtual memory. Even in OS-9 68k the kernel is under 64k in size. Another useful characteristic is that the kernel is modular enabling one to load device drivers any time one pleases. Everything in memory is either a module or the property of a module, and resource sharing is done through this concept.