PE> Can you confirm the operation of dos extenders.  I can understand
PE> that once in protected mode you can access all memory and use 32-bit
PE> instructions.  Now presumably when an application (which I compiled
PE> with watcom c with a dos extender) needs to read from a file, it
PE> would normally call INT 21.

PE> However, the memory you want the data put in is too high, so I would
PE> presume that Watcom would be written so that instead of calling INT
PE> 21 itself, it calls a dos extender function.  The dos extender people
PE> would have a function for every single interrupt.

Not really, you can just pass stuff thru that you dont know needs special
action. You obviously need to do the cpu mode change first, but thats all.

PE> The dos extender people then go and retrieve the stuff into low
PE> memory, then copy it into high memory.  Is all that right?

Thats the general idea. Its considerably more complex than that at times
tho coz for example the drive IO may well be being done with a DMA
controller with its own virtual DMA driver which can DMA directly into
the ram in one go too.

Modern memory managers actually normally run in protected mode for
various reasons and sort of reverse the logic.

--- PQWK202