Int 13 Fn 21  - Hard Disk - Ps/1 And Newer Ps/2 - Read Multiple Disk Sect  [d]

   AH = 21h
   AL = number of sectors to write
   CH = low byte of 12-bit cylinder number
   CL = starting sector (bits 0-5) and bits 8-9 of cylinder (bits 6-7)
   DH = head number (bits 0-5) and bits 10-11 of cylinder (bits 6-7)
   DL = drive number (80h,81h)
   ES:BX -> buffer for data to be read

Return: CF clear if successful
       ES:BX buffer filled
   CF set on error
   AH = status (see #0166 at AH=01h)
Desc:  read from the disk using the Multiple Block mode available on newer
     IDE drives and some hard disk controllers, which generates an
     interrupt only after the end of transferring a group of sectors
     rather than after each sector

Notes: must call AH=24h"PS/1" before using this function
   input values in CL and DH are not range-checked
   the byte at address 0040h:0074h is set to the status of the operation

See Also: AH=02h,AH=22h"PS/1",AH=23h"PS/1",AH=24h"PS/1"