INT 2F U - DOS 5+ - COMMAND.COM INTERFACE
        AX = 5500h
Return: AX = 0000h if an instance of COMMAND.COM is already running
        DS:SI -> entry point table
Notes:  used to access the shareable portion of COMMAND.COM, which may have
          been moved into the HMA; only the primary COMMAND.COM retains this
          portion
        procedures called from a dispatcher in COMMAND's resident portion;
          most assume that the segment address of the resident portion is on
          the stack and are thus not of general use
SeeAlso: AX=5501h

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