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I need to output to two screens from a Macbook Pro 17" I'm looking at buying. My current laptop has a VGA port and an HDMI port, and so it's pretty easy to run a dual-display setup with it. How would I connect my displays to my Macbook?

Both displays are 1080p HDMI computer monitors.

If I have to use Thunderbolt, will it work with Linux? I'm planning on dual-booting.

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4 Answers

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You've pretty much got two options for two external monitors on a MacBook Pro:

A) Two Apple Thunderbolt Displays

This is the least flexible, but highest performing solution. Obvious drawbacks are the cost, and not being able to use your existing displays. This only works on Thunderbolt equipped Macs with a discrete graphics card (i.e. not the 13" MacBook Pro or any MacBook Air, nor the base Mini).

B) DisplayLink adapter

You can use one display directly connected to the Thunderbolt/Mini Displayport with an mDP-HDMI adapter, and run the second one with a DisplayLink adapter. DisplayLink is essentially basic graphics card connected to your computer via USB. Because of the limitations of USB, it's not a high performance solution - don't expect to do any gaming on it. This does allow you to use your existing monitors, and at relatively modest expense. You may also want to check the current status of Lion support, as I remember seeing some posts about bugs relating to DisplayLink adapters - they may have been fixed by now however.

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A) Yeah, I don't really have two grand lying around to go out and buy new Apple displays. –  Naftuli Tzvi Kay Dec 15 '11 at 23:25
    
This is strange at best that I can't daisy chain HDMI converters off of Thunderbolt, but who knows... there seems to be same way of doing it. –  Naftuli Tzvi Kay Dec 15 '11 at 23:26
    
It has to do with how the Displayport signal is encapsulated within the Thunderbolt signal. To pass more than one Displayport signal at a time, it has to be passed via Thunderbolt, which requires a Thunderbolt device to read. In the future it might be possible to have Thunderbolt accessories to enable multiple external monitors, but at the moment, Apple's Thunderbolt Display is the only option. –  robmathers Dec 15 '11 at 23:28
    
Is there a way to use external video cards with my Macbook? I heard that there was a way to do it. If this is possible, then that'd be great. It's just depressing that a $500 laptop bought two years ago has better capabilities with multiple monitors than a brand new $2500 MacBook pro. –  Naftuli Tzvi Kay Dec 15 '11 at 23:47
    
Well, that's essentially what the DisplayLink devices are. There have been a couple products announced that offer an external PCIe slot via Thunderbolt, but expect them to be pretty pricey, targeted at the professional market. Unless you definitely need gaming capability, look into the DisplayLink option. –  robmathers Dec 16 '11 at 0:25
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Two important things will dictate if an arbitrary MacBook Pro will support two monitors:

  • Does your MBP have Intel integrated graphics or one of the nicer discrete graphics chips?
  • Does it have one or two Thunderbolt ports?

If you have Intel's graphics only (the Intel HD Graphics), as found in the 13" MacBook Pro (and the MacBook Air and some Mac minis), you can attach one monitor to the Thunderbolt/mini DisplayPort port.

If you have discrete graphics in addition to the Intel integrated graphics (as found on the 15" and 17" MacBook Pro models), you can attach multiple monitors even if you have only one Thunderbolt port. Remember, though, that all items on the Thunderbolt chain must be Thunderbolt devices until you get to the last item, which can be mini DisplayPort (this is because TB devices have a daisy-chain port; DisplayPort devices are not required to). All adapters for other display plugs that are currently (August 2011) sold are mini DisplayPort, not Thunderbolt, so they'll end the chain. Ergo, the only way to do multiple displays is to have Apple's Thunderbolt display (which has the TB daisy-chain port) and then have an adapter (or just another display) on that. When manufacturers start to make Thunderbolt display adapters, then you can get two of them and hook up whatever displays you want.

Additionally, two Thunderbolt ports allows you to use two Thunderbolt to DVI/DP/whatever adapters rather than buying a true Thunderbolt display that will allow a second non-Thunderbolt graphics adapter to be connected down the chain.

@EmmEff's answer is correct insofar as USB to DVI adapters and their performance issues and the Dual-Link DVI stuff.

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Thanks. This answer is really helpful. I have a 15" Macbook Pro so I'm assuming I have the discrete graphics card (how can I tell for sure?) Unfortunately my monitors are not Thunderbolt devices; just plain old Acer 24" LCD's so I think I'm stuck for now with the USB option for the second monitor. –  Tom Aug 5 '11 at 20:10
    
@Tom As you mentioned in your answer (which isn't really an answer - it should be a comment) you can see the graphics hardware in your machine by going to System Profiler (System Information on Lion) and choosing the "Graphics" or "Displays" option. –  CajunLuke Aug 5 '11 at 22:12
    
I think that was a different Tom that posted that as an answer. I found out that I do indeed have the discrete graphics chip. I'll be waiting eagerly for manufacturers to come out with the Thunderbolt display adapters. Until then I guess I'll be using the USB to DVI for the second monitor. Thanks! –  Tom Aug 6 '11 at 4:17
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I personally do not believe a USB to DVI adapter is acceptable if you're looking for any video performance on the second display. If you absolutely insist on having two external displays, this might be an option.

The Mini DisplayPort to Dual-Link DVI Adapter is for displays requiring a Dual-Link DVI input. AFAIK, it cannot be used for connecting multiple displays.

According to this article, it is possible to connect only one Thunderbolt display to the MacBook Pro, so daisy-chaining is out.

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If the MBP uses Intel integrated graphics, it can support only one external monitor. If it has a discrete graphics card, it may be able to support multiple monitors. –  CajunLuke Aug 5 '11 at 19:34
    
@Cajun My plastic MacBook with integrated graphics can support another monitor just fine with it's mini-dvi port. –  Nathan Greenstein Aug 5 '11 at 19:39
    
@CajunLuke, FWIW, I did not say anything on the contrary. A USB to DVI adapter does not use the built-in graphics support. –  EmmEff Aug 5 '11 at 19:42
    
@Nathan That's correct. One external monitor. In addition to the internal. –  CajunLuke Aug 5 '11 at 19:50
    
@EmmEff True. The article you linked to is wrong. –  CajunLuke Aug 5 '11 at 19:51
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This Anandtech article features a dongle that will convert a DisplayPort signal to two HDMI signals. The resolution is limited, but may be sufficient for what you want to do.

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