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@ssamydla Thanks for your information. I think this not problem is, because benchmark score low than my 650m. I also run benchmark in external LCD, Score is perfect. Anyway, I'll try to search other possible answer. Under the current situation, 2012 iMac's can't use optimus. many thanks!

@ssamydla Thanks for reply. My iMac 2012 late spec: Link Some people believe this CPU has iGPU and apple just disable it. BTW, when I disable 650M "no" got black screen In nvidia experience only show GTX970, but benchmark score very low....

@Tech Inferno Fan thanks for reply! My iMac CPU is i5-3470s, I saw it have HD Graphics 2500 (Link) something I get wrong or the CPU for iMac is Special specifications? drag windowed app to internal LCD is good idea, thanks.

Hi All First, I'm from taiwan so please forgive my poor english....^^" I'm trying to build eGPU, but GTX 970 just can perfect display in external screen. even if I disable 650m(dGPU) still can't display in internal screen. (no black screen, but restart OS will get error need to repair) List my install step below 1.clean install win10 by bootcamp 2.install boot camp driver 3.windows update to newest patch 4.install newest nvidia driver 368.81 5.reboot after restart, I can see GTX970(eGPU) and GT650m(dGPU) at device manager In nvidia experience also can see 970&650m In nvidia control, 970&650m list in CDUA Question is 1.Is the optimus not working? 2.because boot Win10 in GPT not EFI? 3. any else Many thanks.