The Apple Thunderbolt Display Review
by Anand Lal Shimpi on September 23, 2011 2:56 AM EST- Posted in
- Displays
- Mac
- Apple
- Thunderbolt
- Thunderbolt Display
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.
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Ryan Smith - Friday, September 23, 2011 - link
We replaced the video a couple of hours ago with one that has better audio. You shouldn't be seeing any links to the old one (and if you are, please say where).KPOM - Friday, September 23, 2011 - link
Are there any technical reasons for using Eagle Ridge in the Thunderbolt Display instead of Light Ridge, or is it just Apple being Apple? Had they used the latter, it would have been possible to daisy chain a Cinema Display directly to the Thunderbolt Display, right?Also, on page 8, there is a slight error. You say "The MacBook Air is a different story. Not only does it only support two displays, but the Light 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 think you meant to say "Eagle Ridge" controller.
-=Hulk=- - Friday, September 23, 2011 - link
Why does Intel doesn't use the daisy chaining feature of DisplayPort 1.2 instead of encapsulating individual DP v1.1 streams???Ryan Smith - Friday, September 23, 2011 - link
If I had to go out on a limb, a single TB channel doesn't have enough bandwidth for DP 1.2.Trefugl - Friday, September 23, 2011 - link
I really really love the features that thunderbolt adds to the MBAs (e.g. FireWire and GigE), but I don't want to have to upgrade my entire monitor every time I want to upgrade to the next hub (for maybe USB3 support, or more ports, etc). This would only get worse if they started to put GPUs into the monitor, as GPU tech becomes significantly outdated every year or two, whereas a good monitor can last you 5+ years. Why can't they just release a sleek HUB that you can have sitting behind your monitor. Their approach just doesn't make sense if you already have a 27" or 30" monitor (nor for future upgrades).slashbinslashbash - Friday, September 23, 2011 - link
If you already have a 27" or 30" monitor, then yes, this doesn't make as much sense. If you are just now buying such a monitor, then the Thunderbolt Display makes perfect sense. There is nothing keeping you from buying a future box/hub that you describe, and using it between the MBA/MBP and the display (if the box/hub has a built-in GPU) or daisy-chaining it after the display (if you just want USB3 or other ports). That's the great thing about Thunderbolt, you can keep adding on to it. This display is not necessarily the final link in the chain, nor is it necessarily the first link in the chain. It provides useful functionality at a competitive price today, and the add-on capabilities of Thunderbolt will continue to be useful as new tech comes on line.Trefugl - Friday, September 23, 2011 - link
But what happens when the "next cool thing" comes out that we want in our monitors? Do you just replace a perfectly good monitor because you want to upgrade the addons? I suppose my feelings towards this stem more from the iMac, where you trash a good monitor every few years because you want a new all in one PC...slashbinslashbash - Friday, September 23, 2011 - link
Nobody trashes their old iMacs. The secondary market for Macs is huge. It's not like the PC world where your 3-year-old CPU and mobo would go for $100 so you just keep them as backup or put them into a machine for folding or something. With iMacs, if you upgrade at 3 years then you can probably still get around 40-50% of what you paid for it. 2008 iMacs are regularly going for $600+ on eBay. You buy a new one, transfer everything over, and sell the old one. It's almost like buying a car where you 'trade in' your old model.HMTK - Friday, September 23, 2011 - link
This must be a US phenomenon then.jecs - Friday, September 23, 2011 - link
Well, not a US exclusive or phenomenon.It happens worlwide because most Mac laptops or Pro Macs have been traditionally decent machines (not the best or the most specialized but sure not the cheapest). Some people like OSX but doesn't want to expend on new hardware.
And not a phenomenon because this is not exclusive to Macs but to many decent products that age well including speakers, cars, movies or albums and many more things.