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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.
2You are asking 5 different questions far to many in a single question. – Ramhound – 2012-07-30T13:17:10.107
1I 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 – 2012-07-30T14:11:40.777
2The 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 – 2012-07-30T14:58:59.770
@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 – 2012-07-30T16:18:09.163
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 – 2012-07-30T16:38:16.610
Hennes guess is correct. The USB host (that's the technical term for that female he describes) port on the adapter does work like a single port hub. It has lower power capability than the original port so it's best used for plugging into the monitor's built in powered hub/card reader if it has one (like my Dell monitor does). If your monitor does not have a USB hub, it could also be used for a thumbdrive or card reader directly, but not a phone, tablet, or bus powered 2.5 inch Harddrive. Data transfer rates should not be hindered because the adapter does not use USB data. – Bruno Bronosky – 2013-03-12T19:40:01.570