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I have a bunch of mini-Displayport to DVI adapters lying around. Some of them came from Macbooks, some came bundled with ATI video cards, and some I have no idea where they came from. How can I check if the adapters are active (converts DP to DVI signal) or passive (requires a TDMS signal, for example)? Would there be any hints or anything on the adapter that might suggest this?

An example of a specific use case: I have a Radeon 5870 Eyefinity 6 edition (6 miniDP outputs) and it only supports up to two passive DVI connections. I'm trying to figure out if one of the adapters I have is active, so that I could hook up 3 DVI monitors, without having to try out all combinations of them.

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Do you have the make/models of the ones that aren't Apple adapters? –  Alex Moore Apr 22 '13 at 22:04
    
I think the only way might be based on the vendors specs. Even given that I've seen debate on some forums claiming one adapter is passive or active despite a claimed spec to the opposite. –  Brad Patton Apr 22 '13 at 22:16

2 Answers 2

The standard Apple Mini DP to DVI adapter appears to be a passive adapter.

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The easiest way I can think of to know for sure is to find a 1920x1200 monitor laying around somewhere and connect it to that - (I've got two, so it's convenient :) )

In any case, a passive adapter only supports resolutions up to 1920x1080, where active adapters support up to 1920x1200. If you've got a monitor that's 1920x1200 handy, it will be easy to tell by checking what resolution it uses when you connect it.

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