Q38726: Finding Out what Video Adapters Are Installed and Active

Article: Q38726
Product(s): See article
Version(s): 5.10
Operating System(s): MS-DOS
Keyword(s): ENDUSER | video display monitor color monochrome black white b/w mono | mspl13_c
Last Modified: 14-DEC-1988

Question:

I am writing a program that has to determine what adapter boards are
installed in a machine. In addition, it must also determine which
board is active. How can I use the functions supplied with C to get
this information?

Response:

There is no way using the functions we supply to find out what type of
video adapters are installed in your system. There is, however, a
book entitled "Programmer's Guide to PC & PS/2 Video Systems,"
published by Microsoft Press, which has an appendix that has a MASM
example of finding out what adapters are installed. (This example
could be translated into C.)

However, even if you write code to find out what adapters are
installed, there is no simple way to tell the graphics library to
use an adapter other than the one it wants to use. The library will
pick an adapter according to the following rules:

1. If there is a VGA in the system, it uses it regardless of what
   other adapters are installed and regardless of what adapter is
   currently the default adapter. The only way to change this is to
   hook the BIOS INT 10h interrupt as described below.

2. If there is no VGA, it uses the current adapter. This can be set
   with the MODE command in DOS before you start your program.

If you hook INT 10h, you can change the behavior with the VGA to pick
the current adapter. The _setvideomode function makes a call to INT
10h function 1Bh to determine whether a VGA is installed or not. You
can write code to change the return value if the VGA is not the
current adapter, leaving it alone if the VGA is the current adapter.

The _getvideoconfig function only gives information on the current
video mode, as set by _setvideomode. It is not helpful for finding out
what adapters are installed in your system.

You can find out what adapter the library would use by making calls to
_setvideomode. If the mode cannot be selected, _setvideomode will
return zero. For example, if you tried to select a VGA mode and
_setvideomode returned zero, you would know that no VGA was present in
the system. You then could attempt to select an EGA, etc.

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