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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mczak - Friday, September 23, 2011 - link
I'm wondering what the performance would be like? Looks to me like you'd get a far bigger performance hit in this case.Constructor - Friday, September 23, 2011 - link
That would be very interesting indeed.In a discussion over at ars I've been speculating about some of the possible complications with that setup:
http://arstechnica.com/civis/viewtopic.php?t=11558...
(Same user name there.)
Anand, it would be very interesting if you could find out more about the inner workings and the performance consequences of such a combination, possibly confirming or disproving my speculation on the matter.
Over at Macworld they even seem to have made a Cinema display work when plugged in to a Pegasus RAID daisy-chained to a Thunderbolt display. The implications of that and the potential impact on Thunderbolt throughput would be most interesting as well... ;-)
AlexCheng - Friday, September 23, 2011 - link
Sorry guys, but maybe I didn't quite catch it; what exactly is it using as its power supply source? Because it said that the MagSafe port could charge your MacBooks, then where the hell is the cable for its power??Constructor - Friday, September 23, 2011 - link
The display has an ordinary power cable which you'll need to plug into a wall outlet. And the display then powers and charges the MacBok Air/Pro.ltcommanderdata - Friday, September 23, 2011 - link
If Apple goes through with removing the optical drive for the MacBook Pro, hopefully they'll add an optical drive to the Thunderbolt Display. That would make the Thunderbolt Display very complete as a dock.dBoze - Friday, September 23, 2011 - link
Anand,When you mention there is "no analog audio out", I think the inclusion of even analog audio would be a bit of a slap in the face. All Macs in recent history include digital audio through the 1/8" jack via 1/8" TOSLINK, Us Mac users are far too cool for analog ;).
Another solution for digital audio without an extra cable to your MacBook would be using AirPort Express. This will give you a digital or audio connection to your speakers over the network, and you can even plug it into your network via ethernet if your wireless signal isn't too strong. If I recall correctly, you can choose your AirPort Express as the "device for sound output" under the "Output" tab in "Sound" under sys preferences. Of course, you're limited to using AirPlay-compatible applications (iTunes) on the Windows side of things.
Constructor - Friday, September 23, 2011 - link
All recent Macs have both analog (electrical) and digital (optical) audio ports in the same socket. Analog is for convenience, digital is for avoidance of ground loops and of analog signal degradation.An additional audio port (USB/FireWire/Thunderbolt) is possible, if inconvenient.
stanwood - Friday, September 23, 2011 - link
Nice review!A lot of comments about how Apple could have built this display is a way that made it more easily upgradable. This is a PC mentality (which I share). Apple rejects it. Don't waste your time asking for it. If you must have some Mac love, use these 3 simple rules:
1) Buy all your Apple gear in a single release cycle.
1a) Go ahead and upgrade the OS. Those are actually pretty cheap.
2) Use it until you hate it or can't resist getting the new shiny stuff.
3) Give it all to your grandfather, aunt, or Goodwill and return to step 1.
By the time you get to step 3 Apple will have replaced all the important I/Os. There will be no point in trying to upgrade.
mcnabney - Friday, September 23, 2011 - link
Large, high quality displays are expensive, but last a long time. The iMac and displays like this compell people to discard those expensive displays far ahead of their time and likely buy another display of the same size and resolution.My 27" display is on its third computer and it provides better color accuracy than this expensive new one. That is probably my biggest beef with Apple, sending so many nice IPS displays into the trash/closet long before they wear out or become outdated.
slashbinslashbash - Friday, September 23, 2011 - link
Not any more. Starting with the 2010 27" iMac, there was a DisplayPort which was both an input and an output. Now with all the 2011 iMacs having Thunderbolt, they can all be used as displays for other computers with Thunderbolt display output.