[PC] [XT] [AT]
Expects: AH    02H
AL    sector count (see notes)
CH    track (cylinder) number (0-n)    
CL    sector number (1-n)                 (see notes)
DL    drive: 0-3=diskette; 80H-81H=hard disk
DH    head number
ES:BX caller's buffer address
0:078 Diskette Parameter Table  (for diskette operations)
0:104 Hard Disk Parameter Table  (for hard disk operations)
                                                                  
Returns: AH    BIOS disk error code if CF is set to CY
ES:BX caller's buffer will contain requested data (if no error)
                                                                  
Info: This reads the specified sectors into memory at ES:BX.

Notes:   CX is actually used as a 6-bit and 10-bit field to specify
sector and cylinder (this is important on hard disks with more
than 256 cylinders).  CX is laid out as:

        CH             CL        
1 1 1 1 1 1
 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 
CX:  c c c c c c c c C c S s s s s s 
                                 
        high bits of cylinder number

Note that this imposes a "hard stop" low-level limit on the
number of cylinders on a disk (1024).  Some BIOSs may support
larger values by simulating additional heads and translating
each request.

  On diskette reads, this function stops a multi-sector read at
the last sector in a track.

  On hard disks (with XT and AT BIOSes), a multi-sector read
continues on the next higher head of the same cylinder and if
necessary, advances to the next higher cylinder on the first
head.

  Parameters are the same as for INT 13H 03H (write sectors).

  Use INT 13H 0aH (extended read to read data+ECC).

See Also: INT 25H (read absolute sectors)
DOS fn 440dH 61H (IOCTL read track)
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INT 13H 02H: Read Sectors