Date:	Wed, 16 Feb 2000 08:55:02 +0200 (IST)
From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
X-Sender:	eliz AT is
To:	Florian X <dos DOT fire AT aon DOT at>
cc:	djgpp AT delorie DOT com
Subject:	Re: extender/DPMI host/ DPMI surver
In-Reply-To:	<38a9b77a$0$85200@SSP1NO17.highway.telekom.at>
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On Tue, 15 Feb 2000, Florian X wrote:

> What is the difference betweenan extender, a DPMI host, and a DPMI surver?

This is a subject for a book, not for a short message in a news
group...

In a nutshell, a DOS extender and a DPMI server are two ways for
letting protected-mode programs to run on top of DOS.  An extender
does this in a more transparent way: it catches DOS/BIOS calls made
from protected mode and reissues them in real mode after moving the
buffers between conventional and extended memory.  Since the
application never knows its calls were intercepted, the application
code can be the same one as in a real-mode program.

In contrast, the DPMI way provides only primitive services for running
PM code on DOS.  Thus, it needs more processing from the application
which needs to call these services explicitly.  (In DJGPP, this added
processing is mostly handled by the low-level library functions such
as __dpmi_int and dosmemput).

See the "DJGPP Overview" page, accessible from www.delorie.com/djgpp/,
for more about this.

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