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    On PCs, PC/XTs, and PC/ATs with ROM BIOS dated earlier than 11/15/85,
    ES:BX should point to a valid buffer.
 
    On fixed disks, the upper 2 bits of the 10-bit cylinder number are
    placed in the upper 2 bits of register CL.
 
    This function can be used to test whether a readable media is in a
    floppy disk drive. An error may result from the drive motor being off at
    the time of the request, because the ROM BIOS does not automatically wait
    for the drive to come up to speed before attempting the verify operation.
    The requesting program should reset the floppy disk system (Int 13H
    Function 00H) and retry the operation three times before assuming that a
    readable floppy disk is not present.
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