INT 2F U - DOS 4 only SHARE internal - TURN ON FILE SHARING CHECKS
        AX = 1080h
Return: AL = status
            F0h successful
            FFh checking was already on
Note:   DOS 4.x SHARE has dual functions: FCB support for large (>32M) media
          and file sharing checks.  The undocumented commandline flag /NC can
          be used to disable the sharing code.
SeeAlso: AX=1081h