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I want to connect two 2560x1440 displays to a summer 2012 MacBook Pro Retina (MBP from now on). The best way to do it would be to buy two Apple thunderbolt displays, which would connect

Display2 → Thunderbolt → Display1 → Thunderbolt → MacBookPro

Unfortunately, those displays are too expensive, and I want to get two of the same 2560x1440 IPS displays by a cheaper maker, for 1/3 price, as described here:
CodingHorror: The IPS LCD Revolution

These displays connect over Dual-Link-DVI. The latest MBP has two Thunderbolt ports which should act as Mini-DisplayPorts, and I could theoretically just buy two Mini-DisplayPort → Dual-link-DVI adapters from Apple.

This adapter also uses a USB port. Apparently it's meant to provide additional power to the MBP in order for the display not to flicker.

  • Is this really necessary? The Apple product questions (>100 of them) have a single answer that touches on this and it says it "may be needed"? Is it necessary only when the MBP is on battery, or even when it's plugged in?

  • Why would a display's digital signal be using so much power? This MBP has two Thunderbolt ports.

Given all that:

  • Is it possible to add a display (using an adapter) to each of the two Thunderbolt ports for a total of 3 displays (1 internal, 2 externals)? Some video cards only support two displays, even though they have more ports.

  • Or is there a Thunderbolt → Dual Dual-Link DVI adapter of any kind? If I were to purchase Apple's Thunderbolt displays I could just connect everything over a single Thunderbolt port.

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2  
You are asking 5 different questions far to many in a single question. –  Ramhound Jul 30 '12 at 13:17
1  
I tried to reword your question a bit. It looked a little convoluted, but in its current form I guess it can stay like that. The questions you asked are strictly related to each other, so I probably wouldn't split them up. –  slhck Jul 30 '12 at 14:11
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The need for extra power via the USB plug is easily explained: The conversion between display port to [dual link] DVI is an actual conversion. It is not just a cable but it uses additional hardware. This hardware needs power. Some simple hardware can get by with the power from the display port, but most hardware suited for higher resolutions and need more power. Hence the additional USB plug. –  Hennes Jul 30 '12 at 14:58
    
@Hennes, so you're saying that all the power it needs comes from the MBP's USB plug? And the mother USB plug on the other side of the cable is just there so you don't lose on USB ports? Or is the mother USB port there because the MBP's output is not sufficient, which is what I found in a comment on the Apple product page, but in this case, why is it draining that much power? –  user13727 Jul 30 '12 at 16:18
    
It depends on the specific model of the convertor. I never saw one which needed more than one USB plug for (up to 500mWatt) extra power. The one you link you in your OP also shows only one male USB plug. I strongly suspect that the female USB connector next to the DVI connector is just pass-though. However that is guess work on my part. I never had that particular model, nor its manual. –  Hennes Jul 30 '12 at 16:38

5 Answers 5

The mini-displayport to DVI-D Dual Link is of cause possible as mentioned above, when you have a newer Mac Book and what to attach a hires monitor.

There are other options that might be applicable.

  • Using the HDMI output port as it will support up to 4K, but only at 24 Hz. Remember to ensure that the cable and monitor must be compatible with these high resolutions.
  • Using mini-displayport to displayport. No signal conversion is needed and Displayport 1.2 should support 4K at 60 Hz.

Keep in mind that currently the only Apple computer supporting 4K at 60 Hz is the Mac Pro. For some reason the Late 2013 Mac Book Pro Retina only support 4K at 30 Hz. Running Windows 8.1 on this MBPr, allows it to run at full refresh rate, so many threads thinks it's mainly related to a driver issues in OSX 10.9.

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I have a 13" MBP with two thunderbolt ports. I bought two mini display (same profile as thunderbolt) to dvi adaptors at the apple store, and use these for two 23" dell monitors in my office.

No problems at all. Simply open your system prefs to arrange which display should be "home" (left side or right side in my case) and it works as if I had one giant monitor with a black stripe (the two bezels) down the middle.

All for the price of the dell monitors plus the two apple adaptors (about USD 25 each.)

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I used an Altaz Mini DisplayPort to DisplayPort Adapter ($13 on Amazon) to connect a 27 inch (non-Apple) screen to my MBP. No additional USB cable needed for that, and it plugs into the Thunderbolt port. Sadly I have the non-retina MBP 2012, so unless I splurge on Thunderbolt displays, one external screen is all I get.

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Are you referring to the 27 inch Apple Cinema Display? –  PsychoDad Dec 19 '12 at 20:31
    
No, I own a 27" Acer screen. Edited comment above. –  tbrambor Dec 20 '12 at 23:01
    
is the Acer 2560x1440 or 1920x1200? –  PsychoDad Dec 20 '12 at 23:55

Im using a Crossover Gold with my MBP 13" which I connect using a mini DP to DP cable plugged into the thunderbolt out. No need for a dual DVI cable and Im running at full res

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up vote 7 down vote accepted

So, I've finally received my MBP and the Dual-link-DVI to Mini DisplayPort adapter (simply adapter from now on).

The Korean monitor has been more than worth it, it works superbly absolutely great over the digital link.

The adapter doesn't work at all if you don't plug the USB connector in also. If you plug it in, connect the display, then remove the USB plug, it will stop working instantly. So apparently that USB plug is 100% needed.

I happened to have a VGA to Mini DisplayPort adapter lying around, so I've connected a second external display on the second Thunderbolt port. Everything works fine, my MBP now has 3 displays. I plan to replace this with a HDMI cable, since the MBP also has a HDMI port, it should work.

@Hennes commented on my question above, his answer has been very helpful.

Apparently the adapter is an active component, and it needs to be powered. It draws that power from the MBP's USB plug. To avoid losing a USB port on the MBP, the adapter provides another USB port on the other end, where you can connect whichever device was using the USB port. It seems that the adapter piggybacks on the USB port's power line, while just forwarding the others.

I wander if you could plug two of these adapters one into the other's USB port, and both in each thunderbolt port.

Anyway, the setup works great, but it's a LOT of wires to plug in.

If I were to just buy two of Apple's thunderbolt displays, I would only ever have one thunderbolt cable to connect, and the monitors would act as USB hubs too. But that's $2000 compared to $500.

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Don't forget to self select your answer when it allows you to. And Damn, thats one hell of a display array. –  Journeyman Geek Jul 31 '12 at 23:09
    
Which monitor exactly did you get? I'm considering doing the same (two monitors on RMBP) –  Krzysztof Kozmic Aug 12 '12 at 7:35
    
What adapter are you referring to? I ordered an adapter for my 2012 Mac Air that was supposed to be mini display port to dual link DVI but it did not work with the Korean monitor. –  PsychoDad Dec 19 '12 at 20:30
    
this is really strange i have like 4 usb plugs in monitor itself, why i can't just connect minidisplayport->dvi->dvi cable->monitor and then connect usb->usb.. i mean wtf.. why to pay 100$ for bullshit??? IT world is bizarre.. =/ –  holms Mar 5 '13 at 23:25

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