How does Windows pick a resolution when mirroring different displays?

[JasonNVSD]

If you have two different displays connected, then Win+P to "duplicate", I thought it's supposed to select the lowest native resolution of the two. However, some computers don't, and this causes one display to not work. I confirmed that the computer is getting EDID information from both displays.

 

I'm asking this as a general question, but the specs for my particular situation is a HD+ monitor connected by DisplayPort and a XGA projector connected by VGA, both driven by Intel HD Graphics 4000.

[enjay]

I think it picks the lowest resolution common to both devices, assuming it can detect that. Is there a splitter or wall box in between the PC and the projector? If so, can you try connecting directly rather than through that and see what happens...

[JasonNVSD]

Is there a splitter or wall box in between the PC and the projector?

No, nothing like that.

 

It's difficult to google the topic. There must registry keys that control this, but nothing found yet.

[Arthur]

Does the PC have a second (DP, HDMI or DVI) port that you could connect up to the projector to rule out VGA issues?

[JasonNVSD]

Does the PC have a second (DP, HDMI or DVI) port that you could connect up to the projector to rule out VGA issues?

Yes, a second DP. Most XGA projectors are VGA only, but one of the "bad" setups has HDMI. If I can find an adapter, I will try it for curiosity sake.