Compatibility: Win 3.0+
See: 1600H (srvc: is enh386 windows installed?)
1602H (srvc: get enh386 windows entry-point address)
1605H (ntfy: windows is about to startup)
1606H (ntfy: windows is about to terminate)
1607H (ntfy: device call out)
1608H (ntfy: windows initialization is finished)
1609H (ntfy: windows is terminating)

1680H (srvc: release time-slice)
1681H (srvc: begin critical section)
1682H (srvc: end critical section)
1683H (srvc: get current VM ID)
1684H (srvc: get VxD device API entry-point address)
1685H (srvc: switch VMs and callback)
1686H (srvc: detect INT 31h DPMI services)

Notes:   These functions relate to Enhanced-Mode Windows.  They are
fully-documented in the Windows Device Driver Kit (DDK) since
they are usually used as means for a DOS-level device driver to
communicate with Windows and Windows device drivers.

  The services are tools that can be called by utilities, TSRs,
and device drivers to access services provided by Windows.

  The notifications represent INT 2fH fns that are invoked by
Windows.  To receive these notifications, you are expected to
chain into INT 2fH and watch for AX=16xxH.

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INT 2fH 16xxH: Enh386 Windows Services & Notifications