In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units (CPU). 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.
When a processor that supports x86 protected mode is powered on, it begins executing instructions in real mode, in order to maintain backwards compatibility with earlier x86 processors. 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).
Protected mode was first added to the x86 architecture in 1982, with the release of Intel's 80286 (286) processor, and later extended with the release of the 80386 (386) in 1985. 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.
Read more about Protected Mode: History, 386 Additions To Protected Mode, Entering and Exiting Protected Mode, Features, Operating Systems
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