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 (not FFFFh)
   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 (see #2235)
       AL = error code (same as passed to INT 24 in DI)
       AX = 0207h if more than 64K sectors on drive -- use new-style call
   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
   examination of CPWIN386.CPL indicates that if this call fails with
     error 0408h on an old-style (<32M) call, one should retry the
     call with the high bit of the drive number in AL set
   Novell DOS 7 decides whether the old-style or new-style (>32M) version
     of INT 25 must be used solely on the basis of the partition's size,
     thus forcing use of the new-style call even for data in the first
     32M of the partition
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,INT 21/AX=7305h

(Table 2235)
Values for disk I/O 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