INT 1Ah,  04h (4)        Read Real-Time Clock Date                       many

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

       On entry:      AH         04h

       Returns:       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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       Notes:         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.