3 displays attached to a mid-2010 Mac Pro / ATI Radeon 5870

Last week, I sold my MacBook Pro, which means that I am finally back to running on a single machine (plus a MacBook Air for work)¹. I used to run the MBP on a 30″ monitor, using teleport to share a mouse and keyboard across machines, but when I sold the notebook, I decided that I’d like to connect all 3 of my monitors to my Mac Pro. This has proven to be more difficult than I thought it would be.

Apple officially supports connecting 3 monitors to an ATI Radeon HD 5770 or 5870 graphics card. In a knowledge base article, Apple outlines the various configurations that are supported. It’s strangely confusing, but I suppose a very small percentage of the market actually tries to connect 3 displays to a computer.

Here’s what Apple says:

• To connect up to two Mini DisplayPort displays and up to a 30-inch DVI display simultaneously, use the ports without any adapters.
• To connect two DVI displays, use the dual-link DVI port and the Apple Mini DisplayPort to DVI Adapter or the Apple Mini DisplayPort to Dual-Link DVI Adapter (sold separately).
• To connect three DVI displays at once, you must use two Apple Mini DisplayPort to Dual-Link DVI Adapters (sold separately).
• To connect up to three VGA displays simultaneously, use the Mini DisplayPort to VGA adapter and DVI to VGA adapters (sold separately).

Unfortunately, there are a bunch of problems that they also document.

I have the following displays:

• Dell 3008WFP 30″ LCD (DisplayPort, Dual-Link DVI)
• Dell 3007WFP 30″ LCD (Dual-Link DVI)
• Dell U2410 24″ LCD (DisplayPort, DVI)

Because there are two DisplayPort monitors, I thought I would fit into this category:

To connect up to two Mini DisplayPort displays and up to a 30-inch DVI display simultaneously, use the ports without any adapters.

Unfortunately, when I do this, my system goes haywire. The 24″ Dell, which is connected by a Mini DisplayPort to DisplayPort cable, simply goes dark. It turns off, and none of the buttons — not even the power button — do anything. I have to physically disconnect power from the monitor for it to behave properly again.

If I reboot the Mac Pro in this configuration, no monitors power on. When I VNC into the Mac Pro and run System Profiler, it does not even show that I have a graphics card. Removing one display, and the Mac boots up properly.

I have gotten all three monitors to work ONCE in this configuration (2 x Mini DisplayPort -> DisplayPort, 1 x Dual-Link DVI cable), but it failed upon rebooting.

Someone on a discussion thread at Apple Support wrote:

Windows will run the three displays in Mini-DisplayPort to DisplayPort (x2) and DVI without issue – until you need to reboot, and then the power draw makes the video card unrecognizable.

So maybe it’s a power draw issue. He also says that he managed to get everything to work by using 2 x Dual-Link DVI (adapters) and 1 x DVI, but the idea of using two $99 display adapters, each of which also uses a powered USB port, is insulting.

At the moment, I have all 3 monitors working — even upon rebooting — by using only one of the Mini DisplayPort to Dual-Link DVI adapters, replacing the DisplayPort cable leading to the 24″ display.

The final, working configuration:

• Dell 3008WFP 30″ LCD via Mini DisplayPort to DisplayPort cable (monoprice, cheap)
• Dell 3007WFP 30″ LCD via Dual-Link DVI cable
• Dell U2410 24″ LCD via Mini DisplayPort to Apple Dual-Link DVI adapter / DVI cable (adapter requires single USB port for power)

Getting this to work was harder than it should have been.