Alan Clifford wrote in a message to Mike Bilow:

 MB> It is a design decision, not a problem to be fixed.  DOS progams which
 MB> write directly to the hardware in any form cannot be allowed to run
 MB> in background.  OS/2 will allow such programs to run in foreground,
 MB> but will then preserve and restore the state of the VGA hardware when
 MB> switching to or from the task.

 MB> DOS programs which go through BIOS or the VESA video interface can be
 MB> allowed by OS/2 to run in background or in a window, provided that
 MB> the particular video hardware driver is compatible with such
 MB> operation.

 AC> I have a text mode Dos program that updates a time display 
 AC> using a pointer into video memory.  It is running in a window 
 AC> as I write this.

We need to define some terms.  First of all, your DOS program is not
writing into video memory in a window.  That simply cannot happen under
OS/2.  As obvious proof of this, try to explain why your DOS program is in
a window in the first place!

What happens when a DOS program running in a window tries to write to
hardware is that OS/2 will trap the attempt.  In some cases, such as
attempts to write into video memory, OS/2 will virtualize the operation and
let the program think it is writing into memory, but what is really
happening is that OS/2 is maintaining a logical buffer that it maps into
the program's video memory address space, and OS/2 figures out how to
display things from that buffer.  This is why OS/2 can hide, redraw,
resize, move, and change fonts in such windows.

The kind of writing to hardware I was talking about in the above quote,
however, was with regard to programs which attempt to reconfigure the video
card itself, usually by writing to registers.  Like attempts to write to
memory, OS/2 will trap these attempts to write to registers.  Instead of
virtualizing the attempts, however, OS/2 will simply disallow them.
 
-- Mike


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