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I have an ATI Radeon HD 4850 graphics card in my computer. It has two DVI sockets and an S-Video / TV-OUT socket. There are alreay two monitors connected to the two DVI sockets.

I have a third (currently unused) monitor with DVI and VGA (Sub-D) connection.

  1. Is it possible to use this third monitor with this graphics card?

  2. If yes: How do I connect the monitor to the graphics card?

  3. Are there any adapters or cables between S-Video / TV-OUT and DVI or VGA?

I use Linux as OS with the fglrx drivers. While the configuration may become difficult, too, my current problem is the hardware connection.

graphics card specification: http://www.amd.com/us/products/desktop/graphics/ati-radeon-hd-4000/hd-4850/Pages/ati-radeon-hd-4850-specifications.aspx

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Here's a better question: Does that card have 3 RAMDACs? –  Ignacio Vazquez-Abrams Jan 17 '13 at 16:46
    
I added a link to the specification. From the spefication: Two integrated 400 MHz 30-bit RAMDACs. Each supports analog displays connected by VGA at all resolutions up to 2048x15362. –  user63835 Jan 17 '13 at 17:03
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That means even if you can attach a third display it can only mirror what one of the other displays is showing. –  Ignacio Vazquez-Abrams Jan 17 '13 at 17:10
    
Thx for your help. Just want to be sure. Aren't the DVI connections digital? If yes, why do they need the RAMDACs? And wouldn't be at least one of them availible for S-Video? I don't know how flexible the graphics card's architecture is. –  user63835 Jan 17 '13 at 17:22
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DVI-D is only digital. DVI-I and DVI-A both make use of a RAMDAC. –  Ignacio Vazquez-Abrams Jan 17 '13 at 17:28
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2 Answers

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Although I have not looked up your card specifically, most standard video cards will only support 2 video outputs. Even though there is a 3rd connection for s-video, you will not be able to use it concurrently with the 2 DVI outputs.

As for the second part of the question, there are adapters that will convert s-video to VGA, you probably wont want to. S-video is very old technology and is designed for TV. Images from s-video will not look very sharp on a modern LCD, nor will the resolution be very high.

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I did not buy an composite to VGA adapter, yet so I am not 100% sure, but seems like it is not possible to use a third monitor with independent resolution and display content with this graphics card.

Read the comments abhove and this is from the specification of the graphics card:

  • Two independent display controllers

Drive two displays simultaneously with independent resolutions, refresh rates, color controls and video overlays for each display

Thx to Ignacio Vazquez-Abrams

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