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Nvida Dual Head Setup





<for now just pasting in the text of my post to the Linux sig of the LVCG>

I'm sure Jeff will be interested, but I thought I'd write to the whole list.

At last month's (not this month's, i.e., August, not Septemeber) lab meeting, Val brought her tower and two monitors so we could try to get her dual head setup working (using an Nvidia card, I'll try to find the model number--oops, couldn't find it--Val?).

Jeff had done some research and found both the Nvidia README and a thread on some forum talking about that kind of setup (and a guy that couldn't get it to work, due to one typo (a missing quote) and one wrong parameter (iiuc). Anyway, we didn't get it working at that meeting.

Joe and I met Val at her church school yesterday and spent some more time on it and did get it working (BTW, with generic monitors (random monitors available at the lab)).

Basically what we did was add 8 lines to the /etc/X11/XFConfig file (I might have the name wrong) (this comes basically from the thread that Jeff found), and change one parameter (see below) from 1024 to double that (2048) to make the virtual screen width twice the width of a single screen. (With that setting wrong, X failed to start.)

The thread came from http://groups-beta.google.com/group/alt.os.linux.mandrake/browse_thread/thread/17b9dc0a0bfb01d8/0f8e9a9d9477affa?lnk=st&q=nvidia++%2Blinux++%2B%22dual+head%22+%2B%22mandrake+10.1%22&rnum=1&hl=en#0f8e9a9d9477affa

I'll also mention that I once had a dual head setup on my son's computer using two video cards (one a Voodoo3, one either the motherboard's built in SiS730 or a very plain vanilla card (iirc, we may have tried both)). It was somewhat slow, jerky, and temperamental (one example--if you dragged a window between screens and left it partially on each screen, the computer would "hang" for a significant time (I forget how long, but long enough to make us think about rebooting ;-).

The Nvidia thing is a dream compared to that--scrolling is very responsive, leaving a window on both screens caused no problems, etc. (Joe Simpson may try a dual card Xinerama setup on one of his machines, I'll be interested to see how that works for him.)

The above ignores a few basics, not sure I know them all, but in general:

  • make sure the Nvidia card you're using does support dual head (this card worked in Windows XP, and there is a list of model numbers somewhere (in the README, iirc))
  • start by making the basic install of the Nvidia driver (i.e., for a single head)--Val had done this before we started working on the system, so I don't know any of the details. One way of confirming this is to look for a few specific lines (listed in the README), like driver nvidia and similar
  • a large number of Nvidia cards use a "common driver package" (iiuc)--there are a few older legacy Nvidia cards / chipsets that don't work with that driver package and must use legacy drivers--this card works with the common driver package

Also, I'll mention:

  • the Nvidia dual head setup does not use Xinerama, so one of the things to check for during installation is that Xinerama is not started (in the
  • but Nvida supplies sort of a Xinerama compatibility mode (that's not what they called it) so that applications that look for Xinerama (for whatever reason) will know the capability is there. (However, some combinations of hardware and this compatibility mode apparently barf as well, so sometimes this has to be disabled.
  • from the thread, somebody "wasn't able to get TwinView to work
until the '6629' driver came out, but I thought that was related to my hardware"

<Quotes from the thread> <8 lines to add, may possibly also need to add the BusID line, but we didn't (use lspci to get the parameters, we (I) couldn't quite figure out what they should be)>

Section "Device"
    Identifier "device1"
    Driver "nvidia"
    Option "NvAGP" "1"
    Option "DPMS"
    Option "UseEdidFreqs" "1"                       <- Added this line
    Option "TwinView" "1"                   <- Added this line
    Option "TwinViewOrientation" "Clone"    <- Added this line
    Option "DigitalVibrance" "0"            <- Added this line
    Option "SecondMonitorHorizSync" "30-65" <- Added this line
    Option "SecondMonitorVertRefresh" "50-90"       <- Added this line
    Option "ConnectedMonitor" "CRT, CRT"    <- Added this line
    Option "MetaModes" "1024x768 @1024x768,1024x768 @1024x768"      <-
         Added this line
    BusID  "PCI:1:5:0"


  1. You don't need a second monitor section as everything for the second
monitor has to be in the device section. It doesn't hurt anything, though, as you never use it.


I forgot to notice this before, but since you are using an orientation of 'RightOf', your virtual size is only half the width it needs to be. You have two 1280x1024 monitors side-by-side creating one screen 2560x1024. I assume this is what you want.

Section "Screen"
    Identifier "screen1"
    Device "device1"
    Monitor "monitor1"
    DefaultColorDepth 16

    Subsection "Display"
        Depth 8
        Virtual 2560 1024  <- Try this

    Subsection "Display"
        Depth 15
        Virtual 2560 1024  <- Try this

    Subsection "Display"
        Depth 16
        Virtual 2560 1024  <- Try this

    Subsection "Display"
        Depth 24
        Virtual 2560 1024  <- Try this
</Quotes from the thread>

Randy Kramer

PS: Val: Please confirm that the dual head thingie worked OK with your monitors at home. Also, please tell us the model number of your card, as I can't find a note about that.

PPS: Joe (especially), I don't know what I was thinking yesterday--I just tried moving a window offscreen on my single head setup and we get the same behavior that puzzled me yesterday--you can move a window offscreen to the left or right (or up and down)--that's normal behavior. (Sorry, sometimes I'm in a daze wink (So, in conclusion, the particular change we tried to make from the Mandrake setup screen did not work, but, as you noted, the XF86Config file was rewritten, so apparently some changes can be made from that panel.)


  • () RandyKramer - 05 Sep 2005
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Topic revision: r1 - 2005-09-05 - RandyKramer
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