::Protected mode


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In computing, protected mode, also called protected virtual address mode,<ref name="'Protected virtual address mode' usage">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as virtual memory, paging and safe multi-tasking designed to increase an operating system's control over application software.<ref name="i386 additions">{{#invoke:citation/CS1|citation |CitationClass=book }}</ref><ref name="Purpose of protected mode">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

When a processor that supports x86 protected mode is powered on, it begins executing instructions in real mode, in order to maintain backward compatibility with earlier x86 processors.<ref name="Real mode on powered on">{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> Protected mode may only be entered after the system software sets up several descriptor tables and enables the Protection Enable (PE) bit in the control register 0 (CR0).<ref name="Entering protected mode">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Protected mode was first added to the x86 architecture in 1982,<ref name="i286 release date">{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> with the release of Intel's 80286 (286) processor, and later extended with the release of the 80386 (386) in 1985.<ref name="i386 release date">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Due to the enhancements added by protected mode, it has become widely adopted and has become the foundation for all subsequent enhancements to the x86 architecture,<ref name="Foundation">{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> although many of those enhancements, such as added instructions and new registers, also brought benefits to the real mode.

Protected mode sections
Intro   History    386 additions to protected mode    Entering and exiting protected mode    Features    Operating systems    See also    References    External links   

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