INT 2fH 1605H: Windows Is About to Startup

                                                      Compatibility: Win 3.x 
  Expect: AX    1605H
          CX    0000H
          DX    flags: bit 0=1 if standard mode
                       bit 0=0 if enhanced 368 mode
          DI    version number (major in hi byte; minor is low byte)
          DS:SI 0000:0000
  Return: CX    0000H if OK to continue starting Windows
                else  Windows will not start
          DS:SI addr of an Enable/Disable Virtual Mode handler
          ES:BX addr of a Win386_Startup_Info_Structure
    Info: TSRs and DOS-level device drivers may intercept this function as
          a way to be notified when Windows (standard mode or enhanced 386
          mode) is about to start up.  It lets you free up extended memory
          for use by Windows; for instance, DOS's SmartDrive disk cache
          intercepts this call for that purpose.

          By returning CX != 0, you can prevent Windows from running.  In
          that case, you really ought to display a message to ell the user
          what's going on.

          If the CPU is in Virtual 8086 Mode, you must set it back to Real
          Mode and there are several other important steps.  Please check
          the Windows Device Driver Kit (DDK) for full information.

          Your handler will later receive an INT 2fH 1608H notification to
          indicate that windows is actually starting up or an INT 2fH 1609H
          if Windows finds that it can't start.

See Also: INT 2fH 16xxH: Enh386 Windows Services & Notifications
          INT 2fH: Multiplex Interrupt
          DOS Functions