Time, Real

There is no commonly agreed-upon definition of real time. Indeed, the definition of “real time” is dependent on its application and context. Some trace the origins of the term to the missile age in the early 1950s where it was used in the simulations of intercepts of ballistic missiles by analog computers. One can distinguish between the time of the simulation (where events of milliseconds, days, or years could be represented in minutes or hours) and the actual time or real-world “real time” of an event.

In fact, depending on the application, three different meanings can be ascribed to the term real time. As mentioned above, the first meaning is actual time as opposed to simulated or other non-real-world time. For example, a distinction can be made in a live theatrical production between the actual time that transpires during the production (the real time) and the elapsed time of the fictional event (illusory time). In 15 minutes of real or actual time, a period of years may have passed in the story portrayed on stage.

The second meaning of real time is that it occurs immediately, or without delay; that is, it happens almost instantaneously or at the same time. Technological advances, particularly the advent of the Internet and modern information and communication technologies (ICT), have made this type of real time achievable. For example, it was as early as 1988 that Internet relay chat (IRC), a forerunner of instant messaging, was developed by Finnish student Jarkko Oikarinen, enabling people to communicate via the Internet in “real time”; that is, appearing to communicate without any appreciable delay, almost synchronously.

Thus, with the coming of the Internet and other ICTs that allow users to access information from anywhere in the world seemingly instantly, real time as instantaneous access has become generally equated to “online”; for example, online gaming, online communication. The immediacy of the online environment can be contrasted to the batch processing of earlier computer systems where data were collected over time “in batches,” and then submitted all at one time for processing. This resulted in a sizable delay between the collection of data or the query/event and the receipt of results or computer response.

Videoconferencing uses real-time systems that transmit video across networks, displaying it at the other end seemingly instantaneously. Court reporters now routinely use technology called computer-aided transcription (CAT) to make available words spoken in the courtroom as text on computer screens, with just a few seconds' delay; this is, in real time. Live satellite broadcasts allow viewers, for example, in the United States to see events in Iraq in real time. Improvised musical or other artistic works are created at the same time that these are being performed and so are real-time works. with the use of technology and skilled captioners it is now possible to convert the audio portion of a live program or event almost instantaneously into captioned text (real-time captioning).

The third meaning of real time is in its use in computer-controlled systems. Computers are now frequently incorporated or embedded into aircraft, cars, cell phones, home appliances, manufacturing assembly lines, traffic lights, video game consoles, and many other applications that control real-life processes. Computers must therefore be able to respond to the external environment or real-life conditions fast enough to satisfy some requirement (e.g., to deploy an airbag when a car accident occurs). Computers used in space flight must respond quickly to changing conditions to keep the rocket on its course. Robots in factories must respond within a certain time to keep the assembly line moving at optimum speed. To ensure that all operations in the assembly line run smoothly, the robots must respond neither too quickly nor too slowly. Thus, real time in these systems does not necessarily mean fast but rather as fast as required by the external conditions or particular system. So it is possible for a real-time system to be relatively slow, but it must be guaranteed to respond within a specified time. Therefore, the main characteristic of a real-time computer system is not that it is fast but that it has to meet explicit, strict deadlines. If it fails to meet the deadline, negative consequences result, with their severity depending on the particular system. For example, antilock brakes must respond to changing road conditions immediately in order to avoid serious damage to driver and vehicle. Real-time computer systems in which a catastrophic [Page 1311]failure occurs if the “deadline” is missed are called hard real-time systems. In systems known as soft real-time systems, no major catastrophe occurs if the system is slightly delayed. There may just be degradation in service; for example, computer control of an audio and/or video signal that fails to meet its deadline simply results in poor or reduced quality audio or video.

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