[lug] question on Xorg server configuration

Michael J. Hammel mjhammel at graphics-muse.org
Mon Jan 31 13:54:34 MST 2005

On Mon, 2005-01-31 at 14:17, Phil Rasch wrote:
> I have a series of questions that you all may be able to help me with?
> 1) Can anybody tell me whether it is possible to display the same image 
>    simultaneously on an internal and external display  generically using the 
>    xorg server? And if so, can they offer me a generic xorg.conf file to
>    do so?

What exactly do you mean by "internal" and "external"?  On a laptop the
LCD and external VGA are often connected via hardware and all that is
required is to find the key sequence that points the video out both
ports simultaneously.  I do that on my old (very old) IMB Thinkpad when
I do talks using a projector.

> To put these questions into context, I am using the i810 driver, and I
> have no problems configuring it for a dual head machine when the two
> displays are logically adjacent to one another, but I havent found the
> answer when the screens are logically the same.

If you're using two video adapters in a single PC (not a laptop) then
what you describe is overkill - a single adapter with a Y-splitter would
be sufficient.  I'm assuming what you're trying to do is mirror the
content of the first display on the second display.  This is exactly
what happens on the laptop, and what you'd get with a Y-splitter on a

If you're trying to run dual head in the Xserver and are not running
Xinerama then you'll have two distinct desktops.  In that case your
application has to be able to do the image mirroring, which would be
very memory intensive.

If you're running dual head with Xinerama then you can have a single
logical desktop that spans multiple screens.  In that case your
application would still need to know how to display multiple copies of
itself but this time it would do it on the same desktop (which is
programmatically less difficult than the last situation).

However, using dual head in the server - with or without Xinerma - does
not mirror the desktop to both monitors.  Dual head is specifically made
so you don't mirror.  If you're trying to mirror the displays then use a
hardware solution in your laptop or a Y-splitter.  That is much simpler.

Not sure if that helps.  I probably didn't understand the problem
Michael J. Hammel           
The Graphics Muse              Chinese Proverb:
mjhammel at graphics-muse.org          Man who run in front of car get tired

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