Category: <b>DOS-based task switchers/multitaskers</b>
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<pre><b>INT 21 - DoubleDOS - GET VIRTUAL SCREEN ADDRESS</b>

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