资料来源 : Free On-Line Dictionary of Computing

virtual 86 mode
     
         (Or "virtual mode" or "virtual 8086
        mode") An operating mode provided by the {Intel 80386} and
        later processors to allow {real mode} programs to run under
        {operating system}s which use {protected mode}.  In this
        sub-mode of protected mode, an operating environment is
        created which mimics the address calculation in real mode.
     
        In virtual 86 mode the segment {MMU} is practically turned off
        and the {segment register}s exhibit the same behaviour as in
        real mode.  The {page}d MMU, however, still operates.  This
        means that the one megabyte {address space} of real mode can
        be remapped in four kilobyte {page}s to anywhere in the 32 bit
        {physical address} space.  Each page can be protected
        separately from read or write accesses.
     
        Virtual mode is handled on a per-task-basis, so each
        {exception} (from protection violations or {interrupt}s)
        switches the processor back into protected mode.  It is
        therefore possible to have multiple tasks in virtual mode
        which run {concurrent}ly under the control of an operating
        system which runs in protected mode.
     
        Most operating system services in {MS-DOS} systems are called
        by {software interrupt}s, which are a kind of exception.  If
        an MS-DOS application runs in virtual mode under the control
        of a protected mode operating system, each call to MS-DOS
        causes a switch to protected mode.  The operating system
        emulates the MS-DOS service and switches back to the
        application in virtual mode.  From the viewpoint of the
        application nothing differs from real mode.
     
        {Microsoft Windows}, {Windows NT}, and {OS/2} use this feature
        to implement "DOS-boxes" in which both MS-DOS and real mode
        {application program}s can run.