From: Charles Sandmann <sandmann AT new-orleans DOT neosoft DOT com>
Subject: Re: V2 and commercial level programs
To: dj AT stealth DOT ctron DOT com (DJ Delorie)
Date: Wed, 14 Dec 1994 15:06:25 -0600 (CST)
Cc: rossi AT cs DOT unibo DOT it, djgpp AT sun DOT soe DOT clarkson DOT edu

> > A question about that: in VBE paging can be done usign both interrupt and
> > a far procedure call (an interrupt gives you the address to call).
> > Are there any tourble calling such a thing from DPMI?
> 
> The interrupt is OK but slow (mode switch).  The far call won't work
> from protected mode, so there's another mode switch.  1.X added a
> special option to map selector 0x40 to segment 0x40, but you can't
> often do that in DPMI because 0x40 is a ring zero selector, and DPMI
> often gives you lesser rings.

This actually isn't true, all tested DPMI providers allow you to use
selector 0x40 in protected mode.  The DPMI spec says don't rely on it
being that way, but if it is a big speed improvement, I would make it
an option.