Int 13 Fn 4E  - Ibm/ms Int 13 Extensions V2.1 - Set Hardware Configuratio  [d]

   AH = 4Eh
   AL = function
       00h enable prefetch
       01h disable prefetch
       02h set maximum PIO transfer mode
       03h set PIO mode 0
       04h set default PIO transfer mode
       05h enable INT 13 DMA maximum mode
       06h disable INT 13 DMA
   DL = drive number

Return: CF clear if successful
       AH = 00h
       AL = status
       00h command was safe (only affected specified drive)
       01h other devices are affected
   CF set on error
       AH = error code (see #0166)

Note:  DMA and PIO modes are mutually exclusive, so selecting DMA disables
     PIO (for either the specified device or all devices on that
     controller), and selecting PIO disables DMA

See Also: AH=41h"INT 13 Extensions"