Int 21 Fn EC  - Doubledos - Get Virtual Screen Address                     [T]

   AH = ECh

Return: ES = segment of virtual screen
Desc:  determine the address of the virtual screen to which the program
     should write instead of the actual video memory, so that the
     multitasked programs do not interfere with each other's output

Notes: screen address can change if task-switching is on!
   identical to AH=FCh

See Also: INT 10/AH=FEh,AH=FCh"DoubleDOS",INT FC"DoubleDOS"