I was cleaning out my old email, and I ran across this old message to myself from from December 3, 2003. I was telling myself to remember some of the great things about OS 9. If I remember correctly, I even ran an old Dragon emulator to run a copy of the OS image that someone put up.
Thanks to Wikipedia, there is now a good page about OS 9. I highly recommend reading it because I still consider this OS to be a good design.
From what I remember, the OS was much more elegant than any other system. All of the modules were very small, yet still powerful. Re-use was a hall mark of the system. It didn’t have a true MMU, but it was one of the first to support an MMU in the early 1980’s on a simple microprocessor.
Think about it: it supported true multitasking, a unix I/O model. Its ABI was very cool… it used the carry register for boolean returns. You could read the asembly description of a module and understand what was happening very quickly.
(Note to me: look at IDup in ioman.asm)
Where was it weak? It didn’t support threading, tcp, ethernet, large memory sizes, and improved linker technology. For some reason, they had a lot of innovation and then it sort of stopped. I wonder if the original engineers left early in the process.