Int 15h, C1h            Extended BIOS Data Area                          PS/2

    Returns the address of the Extended BIOS Area.

        Entry   AH = C1h

        Return  For PCjr and PC:
                   AH = 80h, CF = 1
                For PC XT, AT, XT 286, Convertible
                   AH = 86h, CF = 1
                For All Others:
                   IF CF is not 1, then ES = Extended BIOS
                                   data area segment address.

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    This service gives you quick access to the extended BIOS data area
    used in the PS/2. If the carry flag is set on return, the extended
    BIOS data area is not being used. If the carry flag is not set,
    the segment address of the extended data area is in ES.

    The ROM BIOS uses the extended data area as a storage area for
    transient data. For example, the addresses of device drivers are
    stored here.