ATi RadeonHD 4850 X2 Tri-Monitor Issue

A friend encountered an odd problem the other day. He has a RadeonHD 4850 X2 with three monitors hooked up. One via HDMI and two via the DVI ports (the monitors are actually just DSUB so he's using DSUB > VGA converters).

Anyway, Windows (7, 64bit) works fine with two of the monitors (the one HDMI and one DVI) but if he tries to enable a third, CCC tells him that he needs to choose one to disable. As far as I'm aware, the 4850 X2 is able to power 4 screens so why is it insisting on only allowing two?

I've spent some time looking this up and the only other incident I can find relating to this is back on the old version 9 drivers where people said you needed to disable Crossfire to get 4 monitors, but you can't disable Crossfire with the later drivers now so that's obviously not an option. It doesn't really make any sense either.

Any light that anyone can shed on this would be appreciated.

Has he only just set it up? Eyefinity requires a displayport monitor for any more than 2 monitors-this probably explains why 2 work and the third doesn't

The 4850 x2 doesn't support eyefinity - that's a 5-series and later thing. So if you're using it in crossfire mode it will only output to two monitors simultaneously.

To get 4 outputs off a 4850 you need to disable crossfire, as you've correctly identified - this allows the card to act as two single 4850s, each capable of powering two displays. If the latest drivers don't allow you to disable the crossfire between the two 4850 cores in the card, the only option would be to uninstall the new drivers, revert to an older set, then disable crossfire to allow using 3 or 4 monitors.

You can't output to three screens over DVI. You would probably need to use some type of active display adaptor to run one of the screens.

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Originally Posted by whobi

... Eyefinity requires a displayport monitor for any more than 2 monitors ...

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Quote:

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Originally Posted by jiggeruk

... You would probably need to use some type of active display adaptor to run one of the screens. ...

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ARGH! The first person getting this wrong I can kind of understand, but someone doing it after my post!?

Guys, please do some research before responding to a request for assistance. The 4850 X2 does not support eyefinity. AFAIK it doesn't even have displayport outputs. I assume the OP's friend has the sapphire version (which I believe was the only one produced) which has 4 DVI ports.

The card can support 2 DVI monitors running in crossfire mode, or it can be "uncoupled" and act as two separate 4850s, in which case you can run up to four monitors off it (but only in extended desktop or cloned desktop mode, *not* as an eyefinity single large surface). So eyefinity and active DP adapters are completely irrelevant to the OP. The OP's friend needs to work out a way to disable the crossfire mode of the board to be able to use it as two separate graphics cards, each supporting 2 DVI connections.

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Originally Posted by scaryjim

ARGH! The first person getting this wrong I can kind of understand, but someone doing it after my post!?

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No offence but I feel a little ARRGH to your response too. I wasn't talking about eyefinity and display port but adaptors like the matrox triple head. The OP would need to check but it should work fine.

Another option would be to buy a cheap second card to drive the 3rd monitor.

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Originally Posted by jiggeruk

No offence but I feel a little ARRGH to your response too. I wasn't talking about eyefinity and display port but adaptors like the matrox triple head. The OP would need to check but it should work fine.

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Ah, fair enough - apologies for the frustrated response! Might be worth clarifying / giving more details in cases like that though ;)

You can pick up allsorts of adaptors for running monitor arrays. A quick search on google for * Multi Monitor Display Adapter * list everything needed to run extended arrays.

I've run six screens over USB in the past and IIRC I used Display Link. Its a piece of cake to set up too.