5.2. DOS and Windows
Most DOS extenders come with some interface to DOS services.
Read their docs about that,
but often, they just simulate int 0x21 and such,
so you do "as if" you are in real mode
(I doubt they have more than stubs
and extend things to work with 32-bit operands;
they most likely will just reflect the interrupt
into the real-mode or vm86 handler).
Docs about DPMI (and much more) can be found on
ftp://x2ftp.oulu.fi/pub/msdos/programming/
(again, the original x2ftp site is closing (no more?), so use a
mirror site).
DJGPP comes with its own (limited)
glibc derivative/subset/replacement, too.
It is possible to cross-compile from Linux to DOS,
see the devel/msdos/ directory
of your local FTP mirror for metalab.unc.edu;
Also see the MOSS DOS-extender from the
Flux project
from the university of Utah.
Other documents and FAQs are more DOS-centered;
we do not recommend DOS development.
Take our 
