Hello,

I tried to go back and reconstruct this thread, but I can't tell who
started it anymore, so I am no longer certain what the original question
was.

In fact, however, there are a number of possibilities of having and
using more than one graphic card in a PC. It is, however, necessary to
know WHY you would want to do so, i.e. what you plan to do with two
separate video output channels.

The oldest use was for CAD applications (e.g. AutoCad) in which a
drawing was made and observed on a (usually very high quality and large
diagonal) SVGA monitor attached to a high-end SVGA or XGA or proprietary
graphic card. The mathematical coordinates and other numeric output were
shown on a (usually small and simple monochrome) monitor attached to a
Hercules graphic card. Since the SVGA and Hercules live at different
addresses there is no conflict here. For this purpose it is fine
solution and is very inexpensive. It must be evident, however, that the
program being used must support this double graphic mode! Otherwise the
whole effort is for nil.

As a historical note, XGA cards could be assigned video addresses and
could therefore be combined as one wished. This is, of course no longer
of any interest because XGA cards have not been made (to the best of my
knowledge) for many years. IBM may still use them in specialized and
dedicated controller hardware. Again, the software you are using must
support this solution.

A newer and somewhat interesting use of multiple monitors is in
"stretching" the video signal over two or more screens. We use a system
like this on a Zeiss confocal scanning laser microscope. The PC uses 2
ELSA graphic cards (PCI) and a specialized driver that simply spreads
the WinNT desktop over two 21" monitors so that one can have a full
microscope image on one screen and a comparable pre-scanned image on the
other - or alternatively, show one 42"-wide picture of the scanned
image. There are many uses for this kind of setup and it requires no
special software. It takes some getting used to as the centre of the
desktop is between the two monitors. I don't recall how ELSA does this,
but I can find out if anyone is interested.

I believe that Matrox has just announced a dual-video output card, but I
don't know any details.

Beyond these "mundane" solutions, there are specialized graphic cards
and "splitters" that allow the use of up to 64 video outputs for huge
multimedia displays, etc. If you need one of these you probably know
where to find out about it.

I hope this is of help and of interest.

Best wishes,

Bruce

-------------------------------
Bruce Boschek - Giessen, Germany

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