How the Computer Accepts Input from the Keyboard

You might think the keyboard simply sends the letter of a pressed key to the computer—after all, that is what appears to happen. Actually, the process of accepting input from the keyboard is more complex, as shown in Fig. 1. When you press a key, a tiny chip called the keyboard controller notes that a key has been pressed. The keyboard controller places a code into pan of its memory called the keyboard buffer, to indicate which key was pressed. The keyboard controller then sends a signal to the computer's system software, notifying it that something has happened at the keyboard. When the system software receives the signal, it determines the appropriate response. When a keystroke has occurred, the system reads the memory location in the keyboard buffer that contains the code of the key that was pressed. The system software then passes that code to the CPU. The keyboard buffer can store many keystrokes at one time. This capability is necessary because some time elapses between the pressing of a key and the computer’s reading of that key from the keyboard buffer. With the keystrokes stored in a buffer, the program can react to them when it is convenient. Of course, this all happens very quickly. Unless the computer is very busy handling multiple tasks, you notice no delay between pressing keys and seeing the letters on your screen. In some computers, the keyboard controller handles input from the computer's keyboard and mouse and stores the settings for both devices. One keyboard setting, the repeat rate, determines how long you must hold down an alphanumeric key before the keyboard will repeat the character and how rapidly the character is retyped while you press the key. You can set the repeat rate to suit your typing speed.