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<h2>21.2 DJGPP environment in v2.x</h2>

<p><em><strong>Q</strong>: There's been this talk about v2 and about <code>go32</code> going away
in that version, but I'm confused on what the new setup will be.  Could
you clarify the details of this change?</em>

<br><p>
<p><strong>A</strong>:  In v1.x of DJGPP, the <code>go32</code> extender was responsible for the
following:

<ul>
<li>Loading and running the application in protected mode.

<li>Managing protected-mode and virtual memory.

<li>"Extending DOS" so that protected-mode programs could issue calls to
real-mode DOS and BIOS services and still run.  (This is mostly done by
switching to real mode and reissuing the interrupt, but some services
require special handling by the extender.)

<li>Handling of hardware interrupts which happen while the CPU is in protected
mode.

<li>Loading 387 emulator (if required).

<li>Loading the graphics driver and working with VGA bank-switching to create
an illusion of a linear video memory.

<li>Command-line and wild-card expansion in a Unix-like fashion. 
</ul>

<p>In v2.x, a minority of these functions are done by a DPMI host, which is
a memory-resident software required to run protected-mode programs under
MS-DOS.  There are a few commercial DPMI hosts (like Quarterdeck's
<code>QDPMI</code>, Qualitas <code>386Max</code>, MS-Windows 3.X and Windows 9X, OS/2,
even Linux), but DJGPP v2 comes with a free DPMI host called
<code>CWSDPMI</code> for those who don't have one already.  Loading the
application into protected-mode memory (a function done in v1.x by
<code>go32</code>) is handled by a 2KB-long real-mode stub which runs at
start-up, before the application's <code>main</code> functions is called
(the stub will also load <code>CWSDPMI</code> if no other DPMI host is
detected).  All the other custom code required to process BIOS- and
DOS-related calls from protected-mode is now built into the library
functions which your program calls, so there is no need for a special
extender, because the application just issues DPMI calls serviced by the
DPMI host.

<p><code>CWSDPMI</code> can be loaded as a TSR, even loaded <code>HIGH</code> into the
HMA/UMB, which will make applications load much faster.

<p><hr>
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