Laptop Dock Question - DVI Splitter?

notapcguru

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Aug 21, 2010
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Hi all,

I have a laptop for work that docks into the following station:

http://accessories.us.dell.com/sna/productdetail.aspx?c=us&l=en&s=bsd&cs=04&sku=331-6307

I am currently working with the laptop screen and one extra monitor that is hooked up through DVI. I would like to work off of two LCD monitors while the laptop is docked with the lid shut.

Of course I could use the VGA port, and that would probably work, but I want the highest resolution possible because I'm reading lots of text. Can I buy a DVI splitter cable? The only reason I think that might not work is because it would "mirror" the screen to both monitors, whereas I want them to be an extension of the desktop. Is there another option I am not thinking of that would work? So I don't have to use the laptop screen? (it's 1920x1080 and is somewhat hard to read.) Thanks everyone for any suggestions!

Thank you!
 

Pinhedd

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Hi there, I got your PM.

According to the specifications for that docking station it has built-in display outputs for DisplayPort, Dual-Link DVI-D, and VGA.

One of the beautiful aspects of DisplayPort is that it can drive two displays via a splitter or daisy-chain. There's a lot of resources out there about how to do this, so I'll leave it up to you to look into that. If your existing display supports DisplayPort you may very will be able to add a second display simply by chaining off of that one.

One of the limitations built into modern GPUs is a limited number of pixel clock generators. This limits the number of display outputs per GPU to two different output sources from any combination of DVI-D/HDMI (they are the essentially the same in this respect), VGA, or DisplayPort. Even if a GPU or station has 4 or more display outputs, only two of them can be used simultaneously. The fun fact is, DisplayPort can use a single pixel clock to drive both its main display and the chained display. In other words, any sort of Eyefinity setup require either the use of DisplayPort, or a professional grade graphics card that supports more than two different clock domains (AMD introduced more generators with the R290/R290X GPUs, but those are for desktops).

For comparison sake, a single HD 7970 can drive 4 displays by using two DisplayPort links with two displays per link.

Problem: Your laptop display counts as a display and will most likely chew up one of the pixel clocks at all times. This leaves one clock generator for any of the other outputs.

There are plenty of DVI-D and HDMI replicators which duplicate the signal to more than one display, but I do not know of any method which allows for a pair of displays to be ganged together into one large display. It may be possible, but Windows would still handle it as a single display and this would look incredibly ugly.

My suggestion would be to invest in a pair of monitors with DisplayPort support (they have to be identical) and chain them off. I've never done this myself and am not sure what else needs to be purchased, but it can be done and it should work.
 
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