two main editions, "Home" (as a replacement for Windows Me for home computing) and "Professional" (as a replacement for Windows 2000 for high-end users). New and updated features User interface While retaining some similarities to previous versions, Windows XP's interface was overhauled with a new visual appearance, with an increased use of alpha compositing effects, drop shadows, and "visual styles", which completely changed the appearance of the operating system. The number of effects enabled are determined by the operating system based on the computer's processing power, and can be enabled or disabled on a case-by-case basis. XP also added ClearType, a new subpixel rendering system designed to improve the appearance of fonts on liquid-crystal displays. A new set of system icons was also introduced. The default wallpaper, Bliss, is a photo of a landscape in the Napa Valley outside Napa, California, with rolling green hills and a blue sky with stratocumulus and cirrus clouds. The Start menu received its first major overhaul in XP, switching to a two-column layout with the ability to list, pin, 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. A "common tasks" list was added, and Windows Explorer's sidebar was updated to use a new task-based design with lists of common actions; the tasks displayed are contextually relevant to the type of content in a folder (e.g. a folder with music displays offers to play all the files in the folder, or burn them to a CD). Fast user switching allows additional users to log into a Windows XP machine without existing users having to close their programs and log out. Although only one user at the time can use the console (i.e. monitor, keyboard, and mouse), previous users can resume their session once they regain control of the console. Service Pack 2 and Service Pack 3 also introduced new features to Windows XP post-release, including the Windows Security Center, Bluetooth support, the executable space protection, Windows Firewall, and support for SDHC cards that are larger than 4 GB and smaller than 32 GB. Infrastructure Windows XP uses prefetching to improve startup and application launch times. It also became possible to revert the installation of an updated