Int 2F Fn 1000  - Share - Installation Check                               [f]

   AX = 1000h

Return: AL = 00h  not installed, OK to install
        01h  not installed, not OK to install
        FFh  installed
BUGS:  values of AL other than 00h put DOS 3.x SHARE into an infinite loop
     (08E9: OR  AL,AL
      08EB: JNZ 08EB) <- the buggy instruction (DOS 3.3)
   values of AL other than described here put PC-DOS 4.00 into the same
     loop (the buggy instructions are the same)

Notes: supported by OS/2 v1.3+ compatibility box, which always returns AL=FFh
   if DOS 4.01 SHARE was automatically loaded, file sharing is in an
     inactive state (due to the undocumented /NC flag used by the autoload
     code) until this call is made
   DOS 5+ chains to the previous handler if AL <> 00h on entry
   Windows Enhanced mode hooks this call and reports that SHARE is
     installed even when it is not

See Also: AX=1080h,INT 21/AH=52h