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Windows XP (stylized as WindowsXP, codenamed Whistler) is an operating system released in 2001 by Microsoft Corporation. It is the successor to Windows 2000 and Windows ME, and is the predecessor to Windows Vista.
Windows XP retains some similarities to previous version, although its interface was overhauled with a new visual appearance, with an increased use of alpha compositing effects, drop shadows, and "visual styles", which completely change the appearance of the operating system. The amount of effects enable are determined by the OS based on the computer's processing power. ClearType, a new font rendering system designed to improve the appearance of fonts on LCD screens, was introduced. A new set of system icons were also introduced.
The Start menu received its first major overhaul on XP, switching to a two-column layout with the ability to pin, list, and display frequently used applications, recently opened documents, and the traditional cascading "All Programs" menu. The taskbar can now group windows opened by a single application into one taskbar button, with a popup menu listing the individual windows. The notification area also hides "inactive" icons by default. The taskbar can also be "locked" to prevent accidental moving or other changes. Windows Explorer's sidebar was also updated to use a new task-based design with a list of common actions.
Fast user switching allows additional users to login to a Windows XP machine without existing users having to close their programs and logging out.
Windows XP was the first version of Windows to introduce Windows Product Activation, which requires that each Windows license be "activated" and tied to a unique ID generated using information from the computer hardware.
Numerous improvements were made to system administration tools such as Windows Installer (an installer API), Disk Defragmenter (a defragmentation tool), Task Manager, NTBackup (a backup software application), and Windows Registry.
Windows XP was originally bundled with Internet Explorer 6 (a web browser), Outlook Express 6 (an email and news client), Windows Messenger (an instant messaging client), and MSN Explorer (an Internet suite).
Other features include DirectX 8.1 (upgradeable to DirectX 9.0c) and faster start-up.