Control Characters
Have you ever wondered about the Unix terminal control characters: Ctl-C to interrupt a program, or Ctl-D to close the terminal? Do you know what Ctl-L does? Why does your computer beep if you press Ctl-G, but not other control keys?
The answer is that by holding down the Control key and typing a letter, you're sending a “control character” to the computer.
But what are these control characters, and why is there a seemingly random association between letters of the alphabet, and functions of the terminal?