Asynchronous communication is the exchange of messages, such as among the hosts on a network or devices in a computer, by reading and responding as schedules permit rather than according to some clock that is synchronized for both the sender and receiver or in real time. It is usually used to describe communications in which data can be transmitted intermittently rather than in a steady stream.
Real time refers to sensing and responding to external events nearly simultaneously with their occurrence. Although real time operations are typically thought of as being fast, this does not necessarily have to be the case: slow systems can allow slow real time operations, and fast operations are not necessarily real time.
Most communications between devices within computers (e.g., between the CPU and disk drives) and between computers and external devices (e.g., modems and printers) are asynchronous. Asynchronous communications also include computer-based exchanges of messages for which the participants need not be available or online at the same time, but, rather, read and respond as their schedules (and desires) permit. Examples include e-mail, discussion boards and text messaging over cell phones.
Direct communication, where all parties involved in the communication are present at the same time is a form of synchronous communication or real time communication. Examples include telephone conversations and instant messaging.
In asynchronous communications it is necessary for the receiver to be able to distinguish between valid data and noise (i.e., random signals). In computer communications, this is usually accomplished through the use of special bits at the beginning and end of each message.
Created October 25, 2005.