A ubiquitous example of serial data communication is the cable linking a keyboard to a personal computer: for every key switch pressed, an ASCII character is transmitted to the computer. An interesting characteristic of this particular communication protocol is the random rate at which the ASCII characters are sent. Because the characters are generated at the rate the computer user happens to type, the rate is completely unpredictable. Consequently, this form of serial data communication is known as asynchronous. Compare and contrast this against synchronous serial data communication, giving an example of a synchronous data communications standard.