Int 15 Fn D100  - Later Ps/2s - Get Number Of Device Descriptor Table (dd  [B]

   AX = D100h
   DX = 0000h (reserved, must set to 0)

Return: BL = size of one DDT entry, in bytes
   CX = number of DDT entries
   AH = return code (see below)
   CF set on error
   CF clear on success

See Also: AH=C0h,AH=C7h,AH=C9h,AX=D101h,AX=D102h,AX=D103h,AX=D104h

Values for return code:
 00h   success
 01h   requested DDT entry not found
 02h   DDT data not valid
 86h   function not supported