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A real-time clock (RTC) is an electronic device (most often in the form of an integrated circuit) that measures the passage of time. Although the term often refers to the devices in personal computers , servers and embedded systems , RTCs are present in almost any electronic device which needs to keep accurate time of day .
Real-time programs must guarantee response within specified time constraints, often referred to as "deadlines". [2] The term "real-time" is also used in simulation to mean that the simulation's clock runs at the same speed as a real clock. Real-time responses are often understood to be in the order of milliseconds, and sometimes microseconds.
Real-time clock, a computer clock that keeps track of the current time Real-time Control System , a reference model architecture suitable for software-intensive, real-time computing Real-time Programming Language , a compiled database programming language which expresses work to be done by a particular time
Real-time operating systems are event-driven and preemptive, meaning the OS can monitor the relevant priority of competing tasks, and make changes to the task priority. Event-driven systems switch between tasks based on their priorities, while time-sharing systems switch the task based on clock interrupts. [1]
Since in concurrent computing the definition of elapsed time is non-trivial, the conceptualization of the elapsed time as measured on a separate, independent wall clock is convenient. Another definition of "wall time" is the measurement of time via a separate, independent clock as opposed to the local system time (internal), i.e. with regard to ...
In contrast, elapsed real time (or simply real time, or wall-clock time) is the time taken from the start of a computer program until the end as measured by an ordinary clock. Elapsed real time includes User time, System time, plus time that the process was not running for any reason, such as when its execution was preempted.
Clock synchronization is a topic in computer science and engineering that aims to coordinate otherwise independent clocks. Even when initially set accurately, real clocks will differ after some amount of time due to clock drift, caused by clocks counting time at slightly different rates. There are several problems that occur as a result of ...
Real-time clocks are electronic devices designed to provide system time, and thereby wall-clock time, to a computer system. (Contrast this with clock signals, designed to provide timing for electronics themselves.)