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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mcturkey - Friday, September 23, 2011 - link
I guess I really don't understand why they can't just make a non-integrated docking station. Use Thunderbolt to connect it if need be, but making it part of the display seems to just add a very unnecessary expense increase if you find yourself needing a new monitor or different/more/better ports in the future.Constructor - Friday, September 23, 2011 - link
As far as I'm aware there are already multiple external PCIe slot housings and other adapters on the way which will effectively serve that purpose.And all of them will be usable with any Mac or PC which has suitable PCIe drivers for the respective ports, so Thunderbolt can indeed provide the long-missing "universal dock".
The complication may be that these drivers should be able to survive hot plugging if you want to avoid having to reboot the machine every time you (dis)connect such an external box (or possibly risk a blue screen / kernel panic otherwise).
Apple just chose to make one specific bundle product; They're leaving all the other possibilities to third parties so far. Once such alternatives are on the market, it's simply your choice.
SameerRamesh - Friday, September 23, 2011 - link
My strong gut feeling suggests that apple will bring only USB 3.0 ports to all their next-gen Macs. Why?Intel's IVB chipsets have native USB 3.0 support. So apple needn't do any extra work there. Furthermore, not adopting an industry standard is a loss. Adding to that, they haven't gone against USB 3.0 now, have they?
Why only USB 3.0 in the next-gen Macs? That's Apple's style!
Constructor - Friday, September 23, 2011 - link
Current Intel chipsets don't have USB3 on chip, so it would take external USB3 controllers to add them to a Mac.The problem is that such external controllers consume precious PCIe 2 lanes which are comparatively scarce with the mobile Intel CPUs. I've not checked the data sheets, but there may simply not be enough PCIe 2 lanes with a mobile Intel CPU to supply both a full-speed-capable external USB3 controller and the Thunderbolt controller at the same time.
Given that choice, I'd say Thunderbolt is the far better option of the two (not least since you can connect USB3 externally through it, but not vice versa).
Desktop CPUs are less constrained, so the iMac and the Mac Pro could have both at the same time even with the current CPU generation (through PCIe plugin cards, if need be).
But I expect Apple to make the jump with the upcoming CPUs which simply provide them on chip with nothing to sacrifice for it.
JasperJanssen - Saturday, September 24, 2011 - link
Ivy Bridge generation Macs will obviously have USB3. Presumably enough of them so that there are no USB2 ports left, as Apple does not like mix and match. And when the Macs have USB3, the display will get it too.quiksilvr - Friday, September 23, 2011 - link
Can you use this Thunderbold Display on another Thunderbolt computer that isnt Mac?Anand Lal Shimpi - Friday, September 23, 2011 - link
Theoretically, yes. We won't know for sure until we see the PC implementations of Thunderbolt but according to Apple if a PC vendor were to integrate Thunderbolt and fully follow the spec the Thunderbolt Display would work.Take care,
Anand
the goat - Friday, September 23, 2011 - link
Somebody already solved this problem decades ago. It is called a laptop docking station. All those cables you are complaining about stay plugged into the docking station.Parhel - Friday, September 23, 2011 - link
That's what's confusing me about this too. Why is this better than, or even as good as, a docking station?With my docking station, I just have to put my laptop on it, and I'm connected to wired network, monitor, mouse and keyboard. I could add another monitor (2 dual link DVI ports), speakers, a printer, and I believe 4 USB devices to that.
I have one docking station at home, one at the office. The dock for home cost me under $100, and it's compatible with both my laptop and my wife's. This seems like a step down from that.
HMTK - Friday, September 23, 2011 - link
If you wan't a razor thin laptop like a MBA there's no room for a docking connector in the laptop. That's probably the main reasons why Apple makes this thing. For their customers it's good.Personally I prefer a docking station exactly for the reasons you stated. I would like to use a generic docking station that's not USB though because now docking stations can only be used with a limited number of machines and there's no compatibility between brands.
Laptop makers are being forced by the EU to make compatible power bricks. Why not do the same for docking stations? Or force them to make a single connector for data and power that's also compatible with a power supply only?