Int 10 Fn 4F07  - Vesa Supervga Bios V1.1+ - Get/set Display Start         [V]

   AX = 4F07h
   BL = subfunction
       00h,80h set display start
       CX = leftmost displayed pixel in scan line
       DX = first displayed scan line
       01h get display start

       Return: BH = 00h
           CX = leftmost displayed pixel in scan line
           DX = first displayed scan line
   BH = 00h (reserved)

Return: AL = 4Fh if function supported
   AH = status
       00h successful
       01h failed

Notes: this function is valid in text modes, provided that values are
     multiplied by the character cell width/height
   subfunction 80h waits until vertical retrace before changing the
     display start address (VBE v2.0+)

See Also: AX=4F01h,AX=4F05h,AX=4F06h