Computers are programmable electronic devices that accept data, execute prerecorded instructions, perform mathematical and logical operations, and output results. Software provides information to a central processing unit (CPU) that executes instructions and controls the operation of other hardware components. Memory allows computers to store data and programs temporarily. Mass storage devices such as tape and disk drives provide long-term storage for large amounts of data. Input devices such as a keyboard and mouse allow users to enter information that can be output on a display screen, printer, self-serve kiosk, or personal digital assistant (PDA). Computers, which require a bus to transmit data from one location to another, are generally classified by size and power. They feature a variety of CPU types and are available with many different operating systems. Spreadsheet, database, work processing, and graphic design applications provide specific functionality.