It is most widely used peripheral input device. It allows manual entering of characters, numbers, punctuation, and symbols that represent data and commands into PC. They are in different forms, shapes, and sizes. Most are manufactured to meet the English standard computer keyboard layout known as QWERTY which refers to the first line of character keys on the top left side of the keyboard. Some keyboards have extra buttons for turning PC on and off, connecting to the Internet, controlling audio CDs, or opening any program designated by the user. The keyboard keys are laid out into three main groups: alphanumeric, punctuation, and special function keys. There are actually three types of keyboards: the original PC keyboard with 84 keys, the AT-style keyboard (which also has 84 keys), and the enhanced keyboard with 101 keys. The main differences between the three designs are the layout and placement of the special function keys. A 6-pin mini-din (PS/2) connector is most commonly used today to connect a keyboard to a computer.