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Chapter 1. Looking Inside Windows XP Pro... > The Windows XP Architecture: Kernel ...

The Windows XP Architecture: Kernel Mode and User Mode

Windows XP is based on the same architecture as Windows NT and Windows 2000. It is a virtual memory operating system that uses two basic modes of operation. The kernel mode is the layer of the operating system's code that is responsible for handling such fundamental operating system items as virtual memory and scheduling which applications will run at any given time. Operating system code that executes in kernel mode has direct access to hardware and memory on the computer. You will sometimes see this referred to as privileged mode. Since the Windows XP Executive Services run in kernel mode, it protects the system's memory against applications that try to write to portions of memory that may otherwise cause a problem.

Note

Executive Services operate in kernel mode and can do things on the computer that user applications cannot. For example, if an application wants to retrieve data from a disk file, it does not contact the disk device drive directly. Instead, it uses the input/output (I/O) manager component of the Executive Services, which then makes the request for the application.



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