On-screen keyboards can be used to type and enter data without using the physical keyboard. An on-screen keyboard may contain all the standard keys including all letters, numbers, symbols, and system keys like Home, End, Insert, Page Up and Page Down, Ctrl, Alt, Caps, and Shift, and can even extend the set of characters available by simulating alternative layouts. These keys can be selected using the mouse or another pointing device, or a single key or small group of keys can be used to cycle through the keys on the screen. The on-screen keyboard is the most common type of virtual keyboard. The accuracy of this keyboard depends only on hitting the right key. The main purpose of an on-screen keyboard is to provide an alternative mechanism for disabled users who cannot use a physical keyboard, or to provide text input on devices lacking a physical keyboard, such as smartphones and tablets.