What registry key or windows file determines where monitors are placed in a multi monitor environment?

"Check out the various keys and folders in

HKEY_CURRENT_CONFIG\System\CurrentControlSet\Control\Video

Specifically in the innermost MonXXXXXXX sub-folders should be Attach.RelativeX and Attach.RelativeY values which are the monitors' location in relation to pixel 0,0.

Strangely when I check a Windows 7 machine here with two monitors, it doesn't seem to show the second monitor. But my XP machine shows all three of mine, so your mileage may vary.

If nothing else it's a place to start!"

"I wish I knew why this worked but I know it does:

To get the monitor to go UP (because negatives aren't allowed by the registry), you have to use values for attach.relativeY like this: 4294967040

Thanks to this forum for helping figure out that part - http://www.ureader.com/msg/164488.aspx

If you change the last 4 digits of that number down, the monitor goes down and vice-versa. This will also work for attach.relativeX. A little tweaking and my setup was back to normal.

Who needs functional drivers pshh"

"A quick update of this old thread for Windows 10.
The Attach.RelativeX and Attach.RelativeY keys are found here:
Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\UnitedVideo\CONTROL\VIDEO\
Below that there will be keys for the machine and sub-keys >00, >01, etc., for each display.
The same rules for negative positioning still apply."

"I found that to activate without logout, you could run
DisplaySwitch.exe /extend

to activate your updated profile in the register instantaneously.
So to one-click automated profile switching , you could batch it up your register settings before calling the above cmd.
For the detail use case, check this guide for creating hotkey or shortcut for extended displays"