Unexpected delay when you set modes on a Windows-based system that has multiple monitors

Applies to: Windows 7 EnterpriseWindows 7 Home BasicWindows 7 Home Premium More

Symptoms


On a computer that's running Windows 7 or Windows 8, users may experience delays when they connect more than two monitors to the system.
The Windows architecture has been optimized for two-monitor scenarios. Typically, display devices support multiple resolutions. Additionally the WDDM graphics card has in built scalars that allow them to scale the desktop image to one of the resolutions that are supported by the display. Therefore, many combinations are possible.

When Windows changes the display configuration between the available monitors on the system and the modes used, it communicates with the WDDM driver to enumerate all these possibilities so that it can provide a rich set of options to the user. However, because of the large number of combinations, this operation may take a long time. Therefore, the user may experience a black screen or an unresponsive mouse pointer for as long as 30 seconds before the image on the desktop is redrawn. The length of this delay increases with the use of larger monitors that are capable of including many modes, as reported in their EDID structures.
Windows 7 and Windows 8 were designed to accommodate all monitors and drivers by giving them the freedom to include as many display modes as possible. Windows processes the mode sets from each active monitor to determine which monitor and which configurations can be displayed. However, there is a performance cost for including large sets of modes from each monitor, because the larger and more complex the mode sets, the more data the system must process to enumerate all the valid combinations.  

The driver can limit the number of modes that it supports, and this helps reduce the time required to complete enumeration of the mode sets. This is the recommended action to take if you decide that the display device enumeration delays are too lengthy. 

Note Drivers can allow enumerations of larger mode sets or of all available modes if you need that flexibility for specific applications.

More Information


Note the following high-level guidelines:
  • The driver must enumerate the native resolutions for each of the connected displays.
  • We recommend that the driver enumerate other lower resolutions that match the aspect ratio of the native resolution.
  • We recommend that the driver enumerate a resolution of 1024 x 768 dots per inch (dpi), because this is a common resolution that's used by many applications.
  • In duplicate mode, the driver must enumerate resolutions that are common to all the affected displays. At the very least, the driver must enumerate a 1024 x 768 resolution.
  • We recommend that driver not enumerate any resolutions that are lower than 1024 x 768 dpi.

    Note However, the following specs must be enumerated for backward-compatibility.

    • 800 x 600 dpi
    • 640 x 480 dpi
    • 32 bits per pixel (bpp) and 0 rotation

    You can also use a registry key to open more modes as necessary.