Int 1Ah, 04h            Read Real-Time Clock Date                        many

    Reads the date from the computer's real-time clock.

        Entry   AH = 04h

        Return  CF   Set if clock not operating; else cleared
                CH = Century (19 or 20) (BCD)
                CL = Year (BCD)
                DH = Month (BCD)
                DL = Day (BCD)

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    All dates are in Binary Coded Decimal (BCD). For example, November
    15, 1987 will be reported as CX = 1987; DX = 1115.

    The real-time clock is the clock that runs even when the computer
    is turned off. A CMOS battery is used so that, even while the
    computer is off, the date, time, and alarm time are maintained.

    This service is available only for ATs, XT-286s, and PC
    Convertibles. Previous machines will report unpredictable results
    (including the state of the Carry Flag).

    The information returned from this service could differ from the
    system date. This is because the real-time clock is read once upon
    system startup, updating the system timer. All other references to
    date use the system timer. If either the real-time clock date is
    changed (via Service 05h) or the system timer is changed (via
    Service 01h), the other date is not changed accordingly.

    Even though the system uses the system timer for date information,
    both the real-time clock and the system timer are updated
    continuously.