When using USB-attached monitor, display configuration may not be retained after reboot


Symptoms


On a computer running Windows 7, you attach a secondary monitor via a USB connection. For example, you may attach a USB Port Replicator device, containing a DVI or VGA port, to the USB port of a laptop computer.

After attaching the secondary monitor, the display configuration may default to "Extend" or "Duplicate." You may then change to a "Computer Only" configuration, in order to turn off the secondary monitor and use only the primary monitor. (You can select a different display configuration by pressing Windows + P keys on the the keyboard.)

If you select a "Computer Only" configuration, and then reboot your computer, you may find that after rebooting, the configuration is changed back to "Extend," "Duplicate," or "Projector Only."

Cause


This behavior occurs because the driver for the USB video adapter enumerates the attached monitor after Windows has already initialized the video subsystem. Therefore, Windows believes the external monitor was plugged in after the computer had already finished booting. When a new monitor is plugged into a running system, Windows 7 attempts to switch to a configuration in which the new monitor is enabled.

Resolution


This is a known issue when using USB-attached displays with Windows 7.

More Information


Windows 7 does not provide native support for video displays which are connected via USB. However, there are some proprietary systems available which enable this type of connection.