Why did my dual monitor set up stop supporting windows shared across both screens?

[fhopper]

Several OS' ago the new operating system stopped supporting windows across my iMac and my Samsung SyncMaster. Apps had always allowed it before now it is either or is my old Samsung 970P DVI monitor no longer "smart" enough?

 

[frou]

It's still supported, you just need to untick "Displays have separate Spaces" in SystemPreferences > MissionControl and then logout/reboot.

 

[fhopper]

It's still supported, you just need to untick "Displays have separate Spaces" in SystemPreferences > MissionControl and then logout/reboot.

Thank you, I have never opened the Mission Control assumed it was another launcher.