IMPLEMENTATION NOTES FOR HIMEM.SYS

    HIMEM.SYS currently supports true AT-compatibles, 386 AT machines,
    IBM PS/2s, AT&T 6300 Plus systems and Hewlett Packard Vectras.

    If HIMEM finds that it cannot properly control the A20 line or if
    there is no extended memory available when HIMEM.SYS is invoked, the
    driver does not install itself. HIMEM.SYS displays the message "High
    Memory Area Unavailable" when this situation occurs.

    If HIMEM finds that the A20 line is already enabled when it is
    invoked, it will NOT change the A20 line's state.  The assumption is
    that whoever enabled it knew what they were doing.  HIMEM.SYS
    displays the message "A20 Line Permanently Enabled" when this
    situation occurs.

    HIMEM.SYS is incompatible with IBM's VDISK.SYS driver and other
    drivers which use the VDISK scheme for allocating extended memory.
    However,  HIMEM does attempt to detect these drivers and will not
    allocate the HMA if one is found.

    HIMEM.SYS supports the optional "/HMAMIN=" parameter.  The valid
    values are decimal numbers between 0 and 63.

    By default, HIMEM.SYS has 32 extended memory handles available for
    use. This number may be adjusted with the "/NUMHANDLES=" parameter.
    The maximum value for this parameter is 128 and the minimum is 0.
    Each handle currently requires 6 bytes of resident space.