Windows Embedded CE has the following restrictions on the number, placement, and characteristics of multiple screens:

• You can connect up to four screens to a device. You must place these screens adjacent to one another and arrange the screens in a horizontal line from left to right.
  
  
• The primary screen is leftmost and contains the point (0,0) at the upper left corner. As a result, Windows Embedded CE does not use negative coordinates for locations on the virtual screen.
  
  
• Whether the primary screen is the same as the VGA or boot display depends on the implementation of the display driver.
  
  
• All screens must have the same bit depth.
  
  
• You cannot change the number of screens while the system is running. You can only change the positions of the screens by physically switching graphics cards.
  
  

To specify the number of screens present in a multiple screen system, set the HKEY_LOCAL_MACHINE\SYSTEM\GDI\MONITORS\TOTAL MONITORSregistry entry equal to the number of screens. You should only set this registry entry to a value between one and four.

To include multiple monitor support in the OS design, you must include Multiple Monitor support from the driver section of the Catalog. Also, under Display Based devices in the Shell and User Interface section of the Catalog, include Multiple Screen Support, which sets the Sysgen variable SYSGEN_MULTIMON=1 and includes Multimon.dll in the OS design.

The bounding rectangle of all of the screens is the virtual screen.The OS represents the coordinates of the virtual screen by signed 16-bit values because many existing messages contain 16-bit values. The following table shows the maximum and minimum values for the boundaries of the virtual screen.