Int 13h, 0Ah            Read Long                                 diagnostics

    Reads one or more long sectors into memory from a fixed disk. A
    long sector is a sector of information plus 4 bytes representing
    the ECC code for the sector. This service can be performed on
    fixed disks only.

        Entry   AH    = 0Ah
                AL    = Number of sectors to read  (1-127)
                CH    = Cylinder number (10-bit value; upper 2 bits in CL)
                CL    = Starting sector number
                DH    = Head number
                DL    = Drive number
                ES:BX = Address of memory buffer

        Return  AH = Status of operation (See Service 01h)
                AL = Number of sectors read
                CF   Set if error, else cleared

    The service reads the specified number of long sectors starting at
    the specified location (head, cylinder, and track) from a fixed
    disk into a buffer starting at ES:BX.


    Note
    This service is for diagnostics only. For a more generalized
    version of the read sector command, see Service 02h, which reads
    sectors for both diskettes and fixed disks. Also see Int 25h
    (DOS), which allows the reading of absolute sectors from any type
    of block device.

    The cylinder number is a ten-bit quantity (0 through 1023). Its
    most significant two bits are in bits 7 and 6 of CL; the remaining
    eight bits are in CH. The starting sector number fits in the
    low-order portion (lower 6 bits) of CL.

    The value returned in AL (number of sectors read) may not give the
    correct number of sectors, even though there no reading error has
    occurred. Use the results of the Carry flag and AH (status flag)
    to determine the status of the operation.

    The number of sectors to read (AL) can be 127 sectors at most.

    If an error is encountered while reading a sector, use Service 0h
    to reset the drive and retry the operation. It is recommended that
    at least 3 retries be attempted before an error is signalled,
    since the error may have resulted from the diskette motor not
    being up to speed.

    Because of the architecture of the DMA channel, an error will
    occur if the buffer in memory for the sectors overlaps a 64K page
    boundary. A 64K page boundary is a memory location which is one of
    the following (10000h, 20000h, 30000h, etc.). Ensure that no part
    of your buffer falls on this boundary. If it does, create a new
    buffer or start the buffer just after the boundary.

    If an error 11h is returned, the data is good but the BIOS is
    reporting that it was corrected via the ECC error-correcting
    algorithm. The error may not occur again if the information is
    written back out.

    For the AT, XT-286, and PC Convertible, the BIOS executes Int 15h,
    Service 90h (Device Busy), for the diskette (Type = 01h) and the
    fixed disk (Type = 00h) prior to waiting for the interrupt. Int
    15h, Service 91h (Interrupt Complete), is executed upon
    completion.