[Coco] Brother Jeremy's OS-9 Level 3 (are you out there, Jeremy?)

Allen Huffman alsplace at pobox.com
Thu Apr 12 18:52:28 EDT 2007

Microware did OS-9 Level 1 (flat memory model, everything in one  
address space), and OS-9 Level 2 (where memory could be remapped).   
CoCo 1/2 used Level 1 (64K) and CoCo 3 used the MMU to map in 512K or  
beyond in 8K blocks, thus Level 2 memory management.

I am not sure where Level 2 was used outside of the 6809 (original)  
version of OS-9.  Every other OS-9 and OS-9000 (today just called  
OS-9) made by Microware was Level 1 (flat memory model).

Level 3 was the NitrOS-9 gang's way to break up the 64K map a bit  
further, giving more memory for processes to use at one time. I ran a  
BBS (StG Net) and it REALLY helped -- the system could be loaded and  
I could run more commands from the same address space.  It took a hit  
on performance, but all the 6309 code and other optimizations  
probably made it come out similar speed-wise to a stock, unpatched  
OS-9 Level 2.

I do not know which "version" current NitrOS-9 uses, but I can't  
really think of any reason not to be using the Level 3.  I seem to  
recall that it split up, if I recall, memory so SCF and maybe other  
file managers had their own 64K block.  So, instead of all your  
drives, etc. having to fit in to 64K, only the base stuff (kernel,  
etc.) had to be there, then serial drivers, etc. had their own map. I  
forget what the magic was, but I seem to recall it letting me  
dynamically load up multiple hard drive drivers and use them, where  
before I had to merge them in to my bootfile to have any room left over.

The "Level 2 Upgrade" (which we may have called Level III wayback  
when) is a souped up MultiVue, basically.

		-- Allen

More information about the Coco mailing list