[Coco] 6309 microprocessor project - 10-24-2003

[KnudsenMJ at aol.com]

In a message dated 10/24/03 2:24:27 PM Eastern Daylight Time, 
jadonaldson at charter.net writes:

>    I thought there was a MAX size that a program could be
>  under OS9. Are you saying that now we can have a multi 
>  100K program running at the same time. I always was told that
>  64K was the max size a program could be.

Without dynamic bank switching, the max size application under OS9-L2 is 
63.5K (taking out the I/O addresses and 256 bytes of interrupt vectors and service 
routines).

Note that system graphics RAM is *not* charged against this 63.5K.  Whew!

If the app does its own dynamic bank switching (memory block mapping) of 8K 
blocks, the total program can approach 2 Megs.  UltiMusE and Roger Taylor's 
Projector-3 (I think he has a new name for it) do this.

Other OS-supported tricks like pipes and data modules, to coordinate an app 
broken up into multiple processes, can also make apps much bigger than 64K.  
UltiMusE is close to 256K total, and could be lots bigger.

The 2 Meg limit has to do with how OS-9 breaks up memory into 8K blocks and 
operates the memory-mapping bits.   It can do at most 256 such blocks.  I used 
to understand the hardware and bit-mangling better, but there is a definite 
limit why OS9 and the Coco3 cannot get over 2M without special new system calls.
--Mike K.