What is the difference between user and kernel modes in operating systems?

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  1. Kernel Mode

    In Kernel mode, the executing code has complete and unrestricted
    access to the underlying hardware. It
    can execute any CPU instruction and
    reference any memory address. Kernel
    mode is generally reserved for the
    lowest-level, most trusted functions
    of the operating system. Crashes in
    kernel mode are catastrophic; they
    will halt the entire PC.

  2. User Mode

    In User mode, the executing code has no ability to directly access
    hardware or reference memory. Code
    running in user mode must delegate to
    system APIs to access hardware or
    memory. Due to the protection afforded
    by this sort of isolation, crashes in
    user mode are always recoverable. Most
    of the code running on your computer
    will execute in user mode.

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Understanding User and Kernel Mode

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