DUAL ATI HD 4870

One 4870 can drive two 30" monitors. Connect one with DVI, and the other to mini display port with a *Mini Display Port -> Dual Link DVI* adapter. I suspect you were trying a regular Mini Display Port -> DVI adapter..

Have you got that to work, Smacman? The mini-display port on my 4780, with two adapters I bought from Apple, neither of them enable the Apple 30"s highest rez, only the DVI port.
With the 30" in the DVI port, my 20" display is easily handled by the MD port.
I have to wonder about what other sizes are being fully supported.

I haven't done it myself, but I know of people that are driving 30" ACDs in full res with Apple's MDP - Dual Link DVI adapter. Maybe this issue is specific to the 4870?

If you're asking if you can have two Radeon 4870's in your MP at the same time, such as something along the lines of ATI CrossFire, I'm pretty sure the answer is no. PCs can use cards like that, but not Macs as far as I know.
The lower end GT120 should be able to work alongside the Radeon, but I've heard some reports that the two cards don't mix well. What that means exactly, I don't know.
There is a company named Geffen, I believe, that sells a workaround unit for the mini-display port. It's pretty expensive last I heard and I don't know if it will ring out the last bit of power for the 30's highest rez either. But at least one company is making the best of a bad Apple invention. There's also a way now to enable displays via USB devices, but I have to wonder about that one.

Look up OWC Mac Sales in Google, I believe they carry both devices and a lot, lot more. Maybe you'll find another option there. Good luck.

You could be right, of course. But it's awfully coincidental to me.
Maybe the 99 dollar adapter would have worked. As it is I believe there were three I could have chosen, with a 30 dollar one being in the middle. When I discovered the Radeon with the two adapters worked fine on the 20", I just assumed that's the way the ports were. Underpowered compared to the DVI port. I didn't go for the 99 dollar card after just having bought two that were supposed to work. Or did one come with the Mac...
Anyway, I wasn't pursuing Apple this time to spend a hundred bucks on another adapter. The other two should have worked on the 30".
The other card I use from time to time, the 285, has two DVI ports and I don't think two 30 inch displays would tax it at all.

Edit: Oh, sorry, I get your thrust now. Just being the 4870. I thought I heard stories about the GT120's MD ports also, but i'm probably mistaken.

Message was edited by: Samsara

Hi,

I am running two (2) 30inch display at full resolution on Mac pro one (1)ATI 4870.

I believe there is not enough power to run two 4870s same for the latest nvidia GTX 285, both of these cards need to be connected to the mother board for more power, I believe I read that you cannot run two of those or add any other secondary video cards for that matter because there is not enough power to run both. I have a geforce 8800 GT in my mac pro and the ati radeon 2600 XT card that came with it is also installed and was thinking of upgrading to a new top of the line card but when I read you can only run one card I have been undecided because I have three monitors running now and I love it. I am using a 30 inch and two twenty two inch monitors. One way around not having a second video card is to get the new usb to dvi cables that sell for around 100 bucks . It does not use open gl acceleration but is good for having your email or other things that take up screen space out of the way of your main monitors. Otherworld computing sells them http://eshop.macsales.com/item/Newer%20Technology/VIDU2DVIA/
If you are looking to join the two cards for gaming purposes I am almost positive you can not because of the lack of power to run the two cards.

Hi Willp1 ,

Is that right? What kind of displays and what kind of mini-display adapter are you using? Thanks for writing in.
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Hi Lance,

I believe your right about the 4870 and 285,... the Mac not having enough power to use both. With the Gt120's though, I think you can fill every slot with one.

A drawback of both cards also is they overhang over the next slot. The cards that work in PCs, I wonder if they actually use both slots.

I think the cards only have one gold connector but have a cable that has to plugin into the mother board for more power, I don't know if they eat up a second slot by hanging over into the next one but I don't think they do. I think both the current top of the line cards Nvidia and ATI use up all the available power for graphics cards but the cheap ones do allow you to multiple slots and only get power from the slot itself.

Thanks, I'll check out the overhang next time I swap cards, which seems to be about every other week now. It kills me not to use the 285 but it's just not significantly better than the 4870, and in some ways worse...

That's the main reason I have not upgraded, I like to use three monitors but I also like having the fastest GPU for gaming but work is more important than play and the new GPU's are still very pricey. You can't have a third monitor without the usb to DVI adapter I mentioned earlier. That is as far as I know the only way to have three monitors while using the latest fastest power hungry GPUs.
Someone should make a third party power supply for the cards so you can run more than one.

I still believe I've heard of people using the GT120 in addition to their main card. I don't remember what the compatibility issues were or if some people didn't have them, but I know that card has been talked about as an option for installing a 3rd display.

As for Dual cards the ATI 4870 draws 75 watts and the PCI-E aux ports can support up to 300 watts.

So there must be a way, But this has solved my problem, Thanks smacman!

The ATI 4870 draws a lot more than 75 watts. Slots 1 and 2 are high-power PCI-e slots and each can provide 75 watts. There are two auxiliary power connectors than can provide 75 watts each. If the ATI 4870 didn't use more than 75 watts, it wouldn't use the auxiliary power ports. If it didn't need more than 150 watts, it would need only one auxiliary power connector. If fact it needs both auxiliary power connectors, so must use more than 150 watt. Since the total PCI power available (all slots plus both auxiliary power connectors) is only 300 watts, there is not enough PCI power for two ATI 4870s.

If you need two high performance cards, you are limited to NVIDIA Quadro FX 4800s. They don't use more than 150 watts each.
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