| virtual 86 mode (Or "virtual mode" or "virtual 8086 mode") An operating mode provided by the and later processors to allow programs to run under s which use . 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 is practically turned off and the s exhibit the same behaviour as in real mode. The d MMU, however, still operates. This means that the one megabyte of real mode can be remapped in four kilobyte s to anywhere in the 32 bit space. Each page can be protected separately from read or write accesses. Virtual mode is handled on a per-task-basis, so each (from protection violations or s) switches the processor back into protected mode. It is therefore possible to have multiple tasks in virtual mode which run ly under the control of an operating system which runs in protected mode. Most operating system services in systems are called by 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. , , and use this feature to implement "DOS-boxes" in which both MS-DOS and real mode s can run. |
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