Communication occurs when there needs to be a movement of information from one place to another. You have it here, but you want it there. Communication involves a sender, or source of the information, a receiver located elsewhere, and a channel that carries the information from sender to receiver. When one person talks to another, the channel consists of soundwaves carried through the air between them. Errors frequently occur, because of interference or “noise” in the channel, because the sender and receiver do not share the same code, or because of physical limitations at either end. A basic method for correcting, or at least detecting, errors is to use “redundancy” – extra information added to the message for this purpose. For example, If I tell you my phone number and then repeat it, I am adding redundancy. Communication between computers also use redundancy. The simplest form is parity: one or more bits added to a message to guarantee an even number of 1’s. In the unit, the instructor conducts a “magic trick” on the class, using parity to determine where a counter was flipped in a 5 x 5 array.