An embedded computer, also called embedded system is a computer that does one thing and one thing only, and usually does it very well. For example, an alarm clock is an embedded computer: it tells the time. Unlike your personal computer, you cannot use your clock to play Tetris. Because of this, we say that embedded computers cannot be programmed, because you cannot install more programs on your clock. Some mobile phones, automatic teller machines, microwave ovens, CD players and cars are operated by embedded computers.