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I have two Radeon 6450 graphics cards in my computer, with three screens. Only the screens plugged into the first graphics card are recognized and configurable in the displays setting panel. How can I use the displays plugged into my second graphics card?

Both cards are present in lspci:

01:00.0 VGA compatible controller: ATI Technologies Inc NI Caicos [AMD RADEON HD 6450]
01:00.1 Audio device: ATI Technologies Inc NI Caicos HDMI Audio [AMD RADEON HD 6450]
02:00.0 VGA compatible controller: ATI Technologies Inc NI Caicos [AMD RADEON HD 6450]
02:00.1 Audio device: ATI Technologies Inc NI Caicos HDMI Audio [AMD RADEON HD 6450]

I'm using the open source driver instead of the proprietary driver because the proprietary driver won't output 1440x2560.

enter image description here

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I don't think is possible –  Christian Vielma Apr 10 '12 at 18:59
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Can you post a screenshot of what you see in System Settings>Displays? The 6450 has three outputs AFAIK...VGA, DVI and HDMI, can't you connect your three monitors on one card? If your monitor doesn't have an HDMI port, can you try with a TV that does? –  titaniumtux Apr 10 '12 at 20:17
    
i've added an image of the displays panel. the HDMI port does indeed give me a third screen, but i would still like to find a way to use the second card as i would like to purchase another 27" screen and would need to use the second card for that. –  notatoad Apr 10 '12 at 20:55
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@ChristianVielma It's definitely possible. Look at USB-VGA adapters. Some of them work, some of them don't but saying using two cards is not possible is surely incorrect. –  hbdgaf Apr 12 '12 at 21:42

2 Answers 2

It is possible. Since Xorg (the Graphical user environment supports multiple separate and or different graphic cards displaying output)

But this feature is incompatible with Unity I've noticed. You will need to run a different desktop environment

Its also quite bothersome to configure, since you have to specify it manually in your /etc/Xorg.conf file.

this thread here has a quite detailed description of how to do it. Prepare for some work!

http://ubuntuforums.org/showthread.php?t=53966 Its old ,but Xorg.conf has been the same for ages.

Just that you will have to switch to a different desktop environment for this to work. maybe old gnome or something similar

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Someone made a similar thing with nvidia graphic boards: https://cornerstone.multitouch.fi/cornerstone-documentation/multiple-graphics-cards maybe some of the steps are of some help. Instead of nvidia-settings you may try aticonfig.

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