Kernel

In computing, the kernel is the central component of most computer operating systems; it is a bridge between applications and the actual data processing done at the hardware level.

The kernel's responsibilities include managing the system's resources (the communication between hardware and software components).

Usually as a basic component of an operating system, a kernel can provide the lowest-level abstraction layer for the resources (especially processors and input / output devices) that application software must control to perform its function.

Kernel Basic Facilities

The kernel's primary purpose is to manage the computer's resources and allow other programs to run and use these resources. Typically, the resources consist of:

The Central Processing Unit (CPU)

This is the most central part of a computer system, responsible for running or executing programs on it. The kernel takes responsibility for deciding at any time which of the many running programs should be allocated to the processor or processors (each of which can usually run only one program at a time)

The Computer's Memory

Memory is used to store both program instructions and data. Typically, both need to be present in memory in order for a program to execute. Often multiple programs will want access to memory, frequently demanding more memory than the computer has available. The kernel is responsible for deciding which memory each process can use, and determining what to do when not enough is available.

Input/Output (I/O) Devices

The kernel allocates requests from applications to perform I/O to an appropriate device, including any device present in the computer, such as keyboard, mouse, disk drives, printers, displays, etc.

Kernels and Microsoft Windows

Microsoft Windows was first released in 1985 as an add-on to MS-DOS. Because of its dependence on another operating system, initial releases of Windows, prior to Windows 95, were considered an operating environment (do not confuse with operating system).

The Microsoft Windows product line continued to evolve through the 1980s and 1990s, culminating with release of the Windows 9x series (upgrading the system's capabilities to 32-bit addressing and pre-emptive multitasking) through the mid 1990s and ending with the release of Windows Me in 2000.

Microsoft also developed Windows NT, an operating system intended for high-end and business users. This line started with the release of Windows NT 3.1 in 1993, and has continued through the years of 2000 with Windows Vista and Windows Server 2008.

The release of Windows XP in October 2001 brought these two product lines together, with the intent of combining the stability of the NT kernel with consumer features from the 9x series.

The architecture of Windows NT's kernel is considered a hybrid kernel because the kernel itself contains tasks such as the Window Manager and the IPC Manager, but several subsystems run in user mode.

The precise breakdown of user mode and kernel mode components has changed from release to release, but with the introduction of the User Mode Driver Framework in Windows Vista, and user-mode thread scheduling in Windows 7, have brought more kernel-mode functionality into user-mode processes.

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