Multi-monitor with the Thunderbolt Display

The Thunderbolt Display has a single Thunderbolt port for daisy chaining additional devices. Each Thunderbolt port can support 7 additional devices, which means 6 devices once you connect the Thunderbolt Display. These devices can be anything Thunderbolt, however you cannot connect a DisplayPort monitor to the Thunderbolt Display directly. If you want to connect another monitor directly to the Thunderbolt Display it must be another Thunderbolt Display. To understand why, we need to look at the architecture of a Thunderbolt controller.

This is the first Thunderbolt controller Intel introduced, codenamed Light Ridge:

You see it has four Thunderbolt channels and two DisplayPort inputs. It also has a single DisplayPort output as well as a DisplayPort passthrough option. What's the difference? If there are only two devices in the chain, the computer and a DisplayPort monitor, you can use the DisplayPort passthrough option bypassing the majority of the logic entirely. This is how the 2011 MacBook Pro can connect directly to a DisplayPort display. Put a Thunderbolt device in between those two devices and you can no longer use the passthrough mode. You have to send a Thunderbolt signal to the Thunderbolt device, and it can then extract the DisplayPort signal and output it. Simply passing DisplayPort through won't work.

I originally believed Apple used the smaller Eagle Ridge controller in its Thunderbolt Display, but now believe that to be incorrect. Upon closer examination of our dissection photos it appears that the 27-inch panel is driven by an embedded DisplayPort (eDP) connection. If I'm right, that would mean the DisplayPort output from the Light Ridge controller is routed to the eDP connector in the display. With its sole DP output occupied by the internal panel, the Thunderbolt Display cannot generate any more DP signals for anything connected directly to its Thunderbolt Port. 

If you connect a Mac to the Thunderbolt Display what is sent is a Thunderbolt signal. DisplayPort is broken off and sent to the display but there's no way to propagate an additional DisplayPort signal to any other non-TB displays in the chain. The output on the Thunderbolt Display is literally a Thunderbolt output, it can't double as DisplayPort.

However, if you connect another Thunderbolt device that uses Light Ridge you can split any additional DisplayPort signals out of the chain. In other words, if you connect the Thunderbolt Display to a Promise Pegasus you can then chain on another DP panel. If you own a 27-inch Cinema Display and were hoping to add the Thunderbolt Display to it on the same Thunderbolt chain, you will need another TB device in between.

There are also the obvious GPU limitations. The 13-inch MacBook Pro only supports two displays (Ivy Bridge will up this to three). If you manage to connect two to the 13 however, Apple will just blank the display on the notebook and drive the two external panels. The MacBook Air is a different story. Not only does it only support two displays, but the Eagle Ridge controller only has a single DisplayPort input so you're not driving more than one external display via a MBA no matter what you do.

I tested multimonitor functionality with a 27-inch LED Cinema Display as well as a second Thunderbolt Display. In the case of the Cinema Display, as expected, I couldn't get video out of the port on the Thunderbolt Display. Connecting the Thunderbolt Display to a Promise Pegasus and then connecting a Cinema Display to it worked however. I also woke up the MacBook Pro's internal display and confirmed that I could get all three functioning simultaneously. There's a definite slowdown in UI frame rate with two 27-inch panels being driven by the MacBook Pro's integrated Radeon HD 6750M. It's not unbearably slow but kiss any dreams of 30 fps goodbye.

I also confirmed that two Thunderbolt Displays worked on the MacBook Pro regardless of the connection configuration.

Power Consumption Windows/Boot Camp Experience
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  • Anand Lal Shimpi - Friday, September 23, 2011 - link

    We do not accept payment for any review, this one included.

    Take care,
    Anand
    Reply
  • Anand Lal Shimpi - Friday, September 23, 2011 - link

    I needed to start somewhere :) The next video review won't be an Apple product ;) And we do try to take great photos of everything we review when possible. I believe some of the best photos to-date have been of Android smartphones imho done by Brian Klug.

    Take care,
    Anand
    Reply
  • Aikouka - Saturday, September 24, 2011 - link

    It's a good review overall, but I do have a comment or two:

    - When switching to a completely different view, I would recommend using a quick transition such as a fade. It's rather jarring to just suddenly switch to a completely different picture like that.

    - If you'd like to make video reviews a bit more common, it might be worthwhile to consider a slight site change to make them a bit more accessible. Some sort of thing (tabs, buttons, etc.) near the top to switch between a text review and a video review.

    I'm trying to figure out though... did you build that entire stage area for the review, or is that a blue screen behind you? The shadows on the lettering made me wonder.
    Reply
  • G-Man - Friday, September 23, 2011 - link

    I'm guessing they make the extra effort on Apple-products, simply because A LOT more people read those articles than the odd generic laptop review.

    If you've been following Anandtech for a while, you will see that they recap and explain (basic) technology and concepts in Apple review, because more people read them, and less tech savvy people read them.

    So it's only natural for them to put extra effort into Apple-reviews.

    PS: Anand, LOVE the video review. Please keep making them! :)
    Reply
  • gevorg - Friday, September 23, 2011 - link

    Anandtech just loves Apple products, hence the special treatment. :) Reply
  • MrX8503 - Friday, September 23, 2011 - link

    Maybe you're the fanboy. Its a good review just like any other, accept it. Reply
  • KoolAidMan1 - Monday, September 26, 2011 - link

    B3an is definitely the fanboy, there is massive bias when he posts in DT threads Reply
  • KoolAidMan1 - Friday, September 23, 2011 - link

    Part of it is that Apple products generally photograph better than others. It is hard to polish a turd, no matter how well you frame or light it. On the other hand, a beautiful object can photograph well under most circumstances.

    As for effort into reviewing Apple products, it is generally because they are on the leading edge of physical interfaces, form factors, and technologies. Three years after the debut of the Macbook Air and now there is a massive push from other companies to deliver comparable machines.

    The reasoning behind the Thunderbolt review is that it points to a very probable future for PCs, one in which your laptop is also your main computer. One option will be to have a laptop that plugs into a Thunderbolt hub (which may or may not be integrated into a display) which has all of your external devices and other things such as a dedicated desktop GPU, etc etc.

    It is interesting how much anti-Apple bias there is here. I'm typing this on my PC but I"m not blind to how vital Apple is to the industry.
    Reply
  • seapeople - Friday, September 23, 2011 - link

    You're comparing the reviews Anand does himself to what some of the other editors do for cheaper/less advanced products. Look at Anand's SSD reviews (especially when its for a new/unique controller) and you'll see the same detail. Reply
  • Kristian Vättö - Saturday, September 24, 2011 - link

    And at the same time, many SSD reviews consist of just benchmarks and a small introduction. Take for example the Samsung 830 SSD review, it's not that massive, mainly because Samsung isn't that big player. Reply

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