Hi Mateusz,

> Actually, by taking a closer look I did find the function 0Ch from both 
> the XMS 2.0 and 3.0 standards. This function returns the physical 
> address (called "base address" for the occasion) of the allocated XMS 
> block as a 32bits integer.
> Now, I could imagine an application (like DOS4GW) that gets such address 
> and puts it into a 24bit field. Such behaviour would effectively limit 
> an application to being able to use only the lowest 15MB of the XMS memory.

Wikipedia says:


* DOOM was the first game to make dos/4g or dos/4gw popular

* it was limited to 64 MB of memory

So I can imagine that Doom uses a really old version of dos/4gw,
which is even more likely to have issues with "too much RAM" ;-)

"We expect to be updating the DOS extender to use the extended XMS
and VCPI calls that allow access to greater than 64MB"

That sounds as if it is in any case limited to XMS 2. Have you made
some comparisons between XMS-only and EMM386-style behaviour of DOOM?


Version 2.01 (1996) mentions some fixes for systems with above 64 MB
of memory and even for properly supporting 64 MB in the first place.

I repeat my advice of using DOS32A instead of working around DOS/4G.

DOS32A is free open source while DOS/4G came in version 1.97 with
old Watcom compilers while 2.01 was only available as paid update:


Which version does your copy of DOOM use?

Cheers, Eric

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