Thunderbolt cables are bidirectional

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The Intel/Apple "Thunderbolt" technology is sexy has heck. It's not the 10gbps speed (being only slightly faster than USB3 5-gbps), but the fact that it exports raw PCIe signals.

But it's a bit flaky. I just bought an Apple 27 inch "Thunderbolt" display to go with the new MacBook Air I just ordered online. Apparently, like many other people, I'm getting an intermittent failure with the screen frequently going black.

Tech-support was pretty clueless, with me explaining to them how to diagnose the problem, such as going to the "System Report" to see what the Thunderbolt controller thinks is attached.

Even worse, they didn't suggest the solution I came up with. Instead of using the built-in "input" cable in the display, I grabbed a normal Thunderbolt cable and connected to the "output" of the display (the output is for daisy chaining to a second monitor, or for hooking up other Thunderbolt devices like RAID arrays).

Had this been a normal display, or normal USB, then connecting to the output would not work. The electrical signals wouldn't work, and the connectors wouldn't match. But this is Thunderbolt, and this sort of thing actually works just fine. There's really no excuse for such interfaces not to be bidirectional.

The standard script when calling about a Thunderbolt display problem should be "Do you have a second cable? Can you connect it to the output port and see what happens?". It's the cable that is the most frequent cause of Thunderbolt problems, you'd think they'd have this worked out by now.

Even after a full year, tech support and the Apple "geniuses" are still pretty clueless about the technology. Two "geniuses" confirmed that the display would work even with non-Thunderbolt DisplayPort connections, which turns out to be false.

When I return it tomorrow, I'm still undecided what I'm going to do. Do I replace with another Thunderbolt display that's likely to have other flaky problems? Or do I just get the non-Thunderbolt display, which costs the same, but works over normal DisplayPort instead? I'm a sucker for sexy, new, but unstable tech, so I'm probably just going to replace it with a monitor that works.

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I resisted my techno-lust and ended up getting the non-Thunderbolt display in exchange (they cost the same). It came down to the fact that I couldn't think of a single good reason to have the Thunderbolt display, but good reason to have the plain DisplayPort version: it works with older computers. I'm typing this on the new monitor with my older Core2 pre-Thunderbolt MacBook Air, and the monitor also works with my Radeon HD 7970 password cracking box. While I'm using this monitor almost exclusively to dock the new MacBook Air arriving Monday, such backwards compatibility is important.

I mentioned to the "Geniuses" how I got the Thunderbolt display to work, using a separate cable to connected to the "output" port. They were all surprised at this. Seems like this is something that Apple should train people on, as it would help diagnose a lot of problems.