Procedure SetVirtualScreen(XSize,YSize:Word)

    Updates VX and VY       : No
    Updates Cursor Position : No

    This creates a virtual screen on the  colour card.  The value of Card
    is ignored.

    Example

    SetVirtualScreen(160,50)

    sets up a virtual screen  of  160x50  in  the current text mode.  The
    virtual screen may be almost any size as long as

    XSize * YSize * 2 < 32768.

    That is, the screen may only use  32  kb  of memory.  The colour card
    will not display more than 32 kb of information.

    Note that the screen may  be  at  most  255  characters  long  and no
    more than (255 + <Screen Width>) wide.

    For example, if you are using a  80x25  screen,  the maximum width is
    335 (255+80) and the maximum  length  is 255.  Also, you may only use
    32 kb of screen display  memory  (hardware  limitation,  8 pages) and
    335*225*2 is 150 kb so may not  be  used  (even if a 2 Megabyte Super
    VGA is installed).