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Protected mode

In computing, protected mode, also called protected virtual address mode,[1] 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.[2][3]

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.[4] Protected mode may only be entered after the system software sets up one descriptor table and enables the Protection Enable (PE) bit in the control register 0 (CR0).[5]

Protected mode was first added to the x86 architecture in 1982,[6] with the release of Intel's 80286 (286) processor, and later extended with the release of the 80386 (386) in 1985.[7] 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,[8] although many of those enhancements, such as added instructions and new registers, also brought benefits to the real mode.

  1. ^ "Memory access control method and system for realizing the same". US Patent 5483646. May 23, 1995. Archived from the original (Patent) on September 26, 2007. Retrieved 2007-07-14. The memory access control system according to claim 4, wherein said first address mode is a real address mode, and said second address mode is a protected virtual address mode.
  2. ^ Intel 64 and IA-32 Architectures Software Developer's Manual Volume 1: Basic Architecture. Intel. May 2019. Section 2.1.3 The Intel 386 Processor (1985).
  3. ^ root (July 14, 2007). "Guide: What does protected mode mean?" (Guide). Delorie Software. Retrieved 2007-07-14. The purpose of protected mode is not to protect your program. The purpose is to protect everyone else (including the operating system) from your program.
  4. ^ Intel 64 and IA-32 Architectures Software Developer's Manual Volume 1: Basic Architecture. Intel. May 2019. Section 3.1 Modes of Operation.
  5. ^ Collins, Robert (2007). "Protected Mode Basics" (PDF). ftp.utcluj.ro. Archived from the original (PDF) on 2011-07-07. Retrieved 2009-07-31.
  6. ^ Intel 64 and IA-32 Architectures Software Developer's Manual Volume 1: Basic Architecture. Intel. May 2019. Section 2.1.2 The Intel 286 Processor (1982).
  7. ^ "Intel Global Citizenship Report 2003". Archived from the original (Timeline) on 2008-03-22. Retrieved 2007-07-14. 1985 Intel launches Intel386 processor
  8. ^ Intel 64 and IA-32 Architectures Software Developer's Manual Volume 1: Basic Architecture. Intel. May 2019. Section 2.1 Brief History of Intel 64 and IA-32 Architecture.

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