How to get 3 1900x1200 monitors working on a 2010 Mac Pro I have a new Mac Pro with a single ATI 5770 card installed. It has two mini-display ports, and one DVI port

I have tried the following configurations:


All 3 DVI connections: This results in one monitor always being black
2 Mini to 2 VGA and one DVI - This results in the VGA monitors having a max resolution of 1920x1080 but defaulting to 1600x1200 due to the aspect ratio. All monitors have a 1920x1200 resolution, but only the DVI port is giving this resolution
All 3 VGA with a DVI to VGA converter on the DVI port - Same result as #2. The monitor plugged into the DVI->VGA port has full resolution. The two Mini->VGA are limited to 1920x1080


My question:

Is this even possible without Apple's dual link adapters?
According to Apple's specs listed under Tech Specs for the Mac Pro it should be able to handle 3 displays at up to 2560 by 1600 pixels over the digital connections. I think the trouble is coming from a little known about techology from AMD called Eyefinity. Which seems to require &quot;Active&quot; Adapters in order to run more than 2 displays at a time.
According to AMD who makes the ATI 5770 card.

What are the basic requirements for connecting multiple displays?
Connecting multiple monitors for AMD Eyefinity technology couldn’t be simpler. There are four easy rules to remember:

The first two monitors can connect to the graphics card with any display output on your product: HDMI, VGA, DVI or DisplayPort.

The third (or greater) display must be connected to the graphics card via DisplayPort.

If your monitor does not have a DisplayPort connection, you will need an inexpensive active DisplayPort adapter for it. DVI to DP adapters can be had for less than $30 USD.2

Every family of GPUs supports a different maximum number of displays.



It looks like you may have the passive  adapters for  the MiniDP to DVI adapters. and hence the trouble and why only 2 displays work when all DVI. Note that the MiniDP to VGA are active adapters.
With the 1920 X 1200 resoultion you will be fine with Single Link adapters, you just need active mini display port to DVI adapters. For some guidance on obtaining compatible adapters see AMD Eyefinity Validated Dongles
As noted in a similar question in the Apple Store:

Q:To use three monitors, does this work with the recently-available active single-link DP to DVI adapters (NOT the simple passive one that Apple [sold])?
Late last year, active single-link DVI adapters became available that function in the same way as the active dual-link adapter that Apple sells, but is intended for use with smaller, single-link monitors. These provide the same added intelligence that the dual-link adapters provide, but only support single-link resolutions. This makes them much cheaper (typically around $30) and they don't don't require the extra power of a USB port.
Can these adapters be used with this card in a mid-2010 (5,1) Mac Pro to drive the second and third monitors in a three-monitor setup?
Answer: To run 3 monitors with this card - 2 of them need to be &quot;active&quot; on the display port connections.
I run the card with 2 display port monitors (an HP and DELL) and 1 DVI monitor - (A 1080p projector with an hdmi/dvi passive adapter). I'm doing this in both a 2010 and 2008 mac pro.
I assume because of this, you can buy the active dual-link dvi/dp adapter and get the same results.
But I can confirm you can't do this with a passive adapter.