Int 21 Fn 64  - Dos 3.2+ Internal - Set Device Driver Lookahead Flag       [D]

   AH = 64h
   AL = flag
       00h (default) call device driver function 5 (non-dest read)
           before INT 21/AH=01h,08h,0Ah
       nonzero don't call driver function 5

Return: nothing (MS-DOS)
   CF set, AX=error code??? (DR DOS 5.0, which does not support this call)

Notes: this function is called by the DOS 3.3+ PRINT.COM
   under MS-DOS, this function does not use any of the DOS-internal stacks
     and may thus be called at any time, even during another DOS call

See Also: AH=01h,AH=08h,AH=0Ah,AX=5D06h