INT 21 - DOS 1+ - SET SYSTEM DATE
        AH = 2Bh
        CX = year (1980-2099)
        DH = month
        DL = day
Return: AL = status
            00h successful
            FFh invalid date, system date unchanged
Note:   DOS 3.3+ also sets CMOS clock
SeeAlso: AH=2Ah,AH=2Dh,INT 1A/AH=05h

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