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

Question

I have a laptop with a USB to VGA adapter which allows me to add a third monitor to my laptop (the second monitor uses the onboard slot).

It worked fine on Windows Vista - you could go into Windows' display settings and Windows would recognize the third monitor and let you drag it around accordingly. With Windows 7, the third monitor literally is not there in Windows' display settings. The driver allows you to display to the third monitor, but you can't move where it is. The display settings are misplaced relative to my other two (if you drag windows over to it, they end up on the bottom when it should be aligned).

I called tech support and they said that there isn't a driver with this functionality for Windows 7 yet. But here's my hunch. The monitor placement is still somewhat similar to where I had it on Vista, it's just off about 500 pixels or so. I think there is either a registry key or driver file somewhere that is telling this monitor where to exist. If I could just modify the number and move it up 500 pixels, it would be in the right place and I don't have to wait 6 months for the company to come out with a new driver.

Any ideas?

Answer 1

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!

Answer 2

For anyone that is looking for the key in Windows 7 it is in one of the folders in:

HKLM\SYSTEM\CurrentControlSet\Control\GraphicsDrivers\Configuration\

Look for Position.cx and Position.cy in each of the subfolders; you have to edit the hex string.

Binary / decimal / hexadecimal converter:

http://www.mathsisfun.com/binary-decimal-hexadecimal-converter.html

Answer 3

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

Answer 4

Subtract the amount you wish to make negative from 4294967296 to get the number you need for the registry. I.e., for 4294967296 - 250 = 4294967046.

For you geeks...

The annoyance here is due to the fact that the registry editor doesn't interpret the 32 bits as anything other than an unsigned decimal integer or a hexadecimal representation of binary data. However, when Windows retrieves that binary data when positioning your displays, it interprets it as a signed integer. In order for Windows to know that a 32-bit signed integer is negative, it sets the last bit to 1 (leftmost) and the rest of the bits are inverted. So -1 will have a binary value of 11111111 11111111 11111111 11111111 (hex: FF FF FF FF). If you translate that into an unsigned decimal integer (like the registry editor does), you get 4,294,967,295. So, for our purposes, 0 equates to 4,294,967,296 which you can simply add your negative number to in order to get the unsigned decimal integer you need that the registry editor saves in binary form and that the system will later interpret as a negatively-signed integer.

Answer 5

Instead of calculating negative values it may be easier to understand if you keep all values positive by making a logical 0,0 at the physical top left of a virtual box you would draw if you tried to surround all the monitors. Think like when you move a monitor up and left, that you are really pushing the others away to the right and down.

For example, I had 1280x1024 and 1920x1200 monitor with the first smaller one defaulting to the top right side of the second, not the bottom left of the first where it is physically positioned (left) and aligns-with (bottom edge is at same height, the top is lower of course because it's not as high).

So to start with the second 1920x1080 monitor was at position 0,0 and the first at 1920,0. Instead of trying to calculate negative -(1920 + 1280), (1200 - 1024) for the first monitor I just put the first monitor at all positive values 0,(1200 -1024) and the second at 1280, 0.

Logging off Windows then logging back on applied the settings for me. It's also useful to know that this works on Windows Hyper-V Server (I just did this on 2012 R2 which means these settings still work in Windows 8 and 8.1). That's really useful for people locked out of the screen resolution settings but trying to achieve a "bare metal" style host PC (you hardly ever have to update or reboot) and work purely with virtual machines inside via Remote Desktop (copy that from another machine).

Thanks to techie007 for the original answer, that was the key to work all this out. If you mark this variant useful don't forget to "up" his answer and the question too.