Int 25  - DOS 1+ - Absolute Disk Read (except Partitions > 32m)            [D]

   AL = drive number (00h = A:, 01h = B:, etc)
   CX = number of sectors to read
   DX = starting logical sector number (0000h - highest sector on drive)
   DS:BX -> buffer for data

Return: CF clear if successful
   CF set on error
       AH = status
        80h device failed to respond (timeout)
        40h seek operation failed
        20h controller failed
        10h data error (bad CRC)
        08h DMA failure
        04h requested sector not found
        03h write-protected disk (INT 26 only)
        02h bad address mark
        01h bad command
       AL = error code (same as passed to INT 24 in DI)
       AX = 0207h if more than 64K sectors on drive
   may destroy all other registers except segment registers

Notes: original flags are left on stack, and must be popped by caller
   this call bypasses the DOS filesystem
BUGS:  DOS 3.1 through 3.3 set the word at ES:[BP+1Eh] to FFFFh if AL is an
     invalid drive number
   DR-DOS 3.41 will return with a jump instead of RETF, leaving the
     wrong number of bytes on the stack; use the huge-partition version
     (INT 25/CX=FFFFh) for all partition sizes under DR-DOS 3.41

See Also: INT 13/AH=02h,INT 25/CX=FFFFh,INT 26