A virtual keyboard is a feature of a computer program or a program in and of itself that acts as a virtual extension of a controller, often with fewer buttons than a keyboard would have. In the world of desktop PCs, the Windows XP program On-Screen Keyboard acts as a virtual keyboard that can be operated with a computer mouse. In stylus-operated personal data assistants it is common for the user to input text by tapping a virtual keyboard built into the operating system of the PDA.