3-15. REAL TINE PROCESSING
a. Real Time. Over 30 definitions can be found in the literature for real time.
This term has caused so much controversy that some would like to see it dropped
entirely. Like on-line systems, real time systems transmit data by means of
communications lines to a central computer. Both use direct access media and require
direct access processing. Like on-line systems, real time involves direct on-line
interaction between the user and the computer, but real time functions under severe
time limitations. Real time implies a response that takes place over an extremely short
period of time, with results returned to the point of origin in time to allow change or
correction if necessary. Real time can be thought of as an extremely quick on-line
response system. A real time processing operation is in parallel time relationship with
an ongoing activity and producing information quickly enough to be useful in controlling
the event.
real time processing: the capability of a system to receive data, process it, and
provide output fast enough to control or affect an activity being performed.
Response time is almost instantaneous.
b. Real Time vs. On-line Systems. A real time processing system is generally
considered on-line (connected directly to a host computer). This interrelationship is
demonstrated by the fact that some sources actually refer to real time as on-line real
time processing. On-line processing, on the other hand, is not always real time. Real
time requires split-second access to up to the minute records, instant access in both
directions (input and output). Data provided to the astronauts on a manned space flight
would be real time. Also, many remote stations may be tied directly by high-speed
communications equipment into the central processor; several stations may be
operating simultaneously. Files may be updated each minute, and inquiries may be
answered by split-second access to up-to-the-minute records. Originally used by the
national defense system and for the space program, real time was subsequently
adapted for commercial uses, such as on-line banking and airline reservations. Airlines
use real time processing to control inventory and book seats. When you call your travel
agent, she records several codes into a small keyboard on her desk. Within seconds a
display screen shows several possible routes, with the airline flight number and arrival
and departure times of each connecting flight. She tells you the choices, and you select
the one you prefer. Another entry confirms your reservations with each airline and
prints your tickets. The ticket indicates your total fare, including taxes, and shows the
share of the fare for each participating airline. The whole transaction takes less than a
minute. In the x-ray field, real time processing means that an image can be displayed
for viewing as scanning is in progress.
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