If you look at the current 2010 Mac Pro specs, it says that with either one ATI 5770 or one ATI 5870 the Mac Pro can drive three monitors.  In a caveat at the bottom of the page, it says:

2. Connecting more than three displays requires installation of two ATI Radeon HD 5770 graphics cards.

This led me (and many others) to believe that connecting three displays was as simple as plugging them in.  The Mac Pro’s 5870 can display on three monitors, but that’s not all the story.  After spending several days working on this and an hour on the phone with two levels of tech support at AppleCare, I’ve learned the whole story (well, most of it).

If you read ATI’s specs on the 5870, it says (in a caveat at the bottom of the page):

Driver version 8.66 (Catalyst 9.10) or above is required to support ATI Eyefinity technology and to enable a third display you require one panel with a DisplayPort connector

Sure, Macs don’t use the PC Catalyst drivers, but this seemed like the 5870 should be able to display on three monitors without much headache.

After my Mac Pro was shipped, Apple posted a support article to their website that talked about supported display configurations of the new Mac Pro video cards.  This was the first indication from Apple that if you used DVI monitors, you were in for a few surprises.  In that article it states that to connect three monitors with DVI, you had to use two of Apple’s Mini DisplayPort to Dual-Link DVI Adapters (part number MB571Z/A).  Given the ATI spec on the 5870, it doesn’t make sense to me when you need two of these.  The folks at AppleCare verified this though.  You need two of them.  I asked AppleCare why this appears to differ from the ATI spec on the 5870 and they didn’t have an answer.

A new Apple Support article just showed up that further details the issues with three displays on the new Mac Pros.  In that article, Apple states that if you connect three monitors one of them “may turn black” or “no longer appear in the Graphics tab of System Profiler.”

… one of the following issues may occur:

• When using a DVI connection, a Mini DisplayPort, and an HDMI connection, the display connected via DVI may turn black.
• When using a DVI connection and two HDMI displays, the display connected via DVI may turn black.
• When using a DVI connection and a HDMI connection, adding an additional HDMI connection or a Mini DisplayPort connection may cause the initially-connected HDMI device to no longer appear in the Graphics tab of System Profiler.

The article goes on to say:

Resolution

When three displays are in use with Mac Pro (Mid 2010), only one DVI or HDMI device should be used.  Note: The Mini DisplayPort to DVI Adapter (different from the Apple Mini DisplayPort to Dual-Link DVI adapter) is considered a DVI device.

So, now we know.  It’s easy to connect three DVI monitors to your shiny new 2010 Mac Pro, but it’ll cost you.  The solution is to use two of the $99 Mini DisplayPort to Dual-Link DVI connectors.  There are several frustrating things with this however.  First, $200 is a (how shall I say this…) “silly” amount to spend on adapters when that’s roughly what an entire 5770 video card costs.  Because the 5870 uses both of the Mac Pro’s PCIe power adapters, you can’t add a 5770 to a system with an existing 5870.  When I asked AppleCare about adding a 5770, they told me it wasn’t a supported configuration and my system was already “maxed out.”  There may be a way to get power from a non-used SATA power connector to drive another graphics card, but that’s not a supported configuration by Apple.

The second frustrating thing is that Apple isn’t currently upfront about these limitations in their sales information. The only caveat about monitors on their sales pages tells you to buy the two 5770 option if you want more than three monitors.  Two 5770s and one 5870 are in the same order of magnitude in speed.  If you want to drive three (or four) non-DisplayPort monitors, the best way to spend your money is on two 5770s instead of a 5870 with a bunch of $99 adapters.

I sent Apple a request to update their sales information to be more clear.  It’d be much better customer relations if they were upfront about which Mac Pro configurations supported each display configuration.  If you’ve been bit by this, you should do the same.  You can leave feedback to Apple here: http://apple.com/feedback

In the grand scheme of things, this isn’t the end of the world.  I bought the new Mac Pro mostly for the power.  In my “real world” benchmark tests, the new 2010 8-core 2.4GHz Mac Pro is roughly 5 times as fast as my 2008 iMac at compiling my iPhone games Air Hockey and Doodle Hockey.  It’s loads faster at After Effects renders.  On OpenCL tasks that can jump on the GPU, the new Mac Pro with a 5870 should really shine.  It crushes my old computer in everything it does.  A new $4000 computer better crush an old $1200 computer though.  I won’t be taking back my Mac Pro.  Still, it’d be nice for everyone to know about all the caveats with new equipment before they drop the cash on it.

So, you still want to drive three DVI monitors with your single graphics card 2010 Mac Pro?  Get two Apple Mini DisplayPort to Dual-Link DVI Adapters for $99 each.  If you want to stray from Apple branded products, you can try similar adapters from MonoPrice at $67 each (these don’t have USB output though and I haven’t verified that they work).

Now you know.  Good luck!

Please send the cards to cards@acceleroto.com ASAP!