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Real-Time Clock (RTC)

Definition - What does Real-Time Clock (RTC) mean?

A real-time clock (RTC) is a computer clock, usually in the form of an integrated circuit that is solely built for keeping time. Naturally, it counts hours, minutes, seconds, months, days and even years. RTCs can be found running in personal computers, embedded systems and servers, and are present in any electronic device that may require accurate time keeping. Being able to still function even when the computer is powered down through a battery or independently from the system’s main power is fundamental.

Techopedia explains Real-Time Clock (RTC)

RTCs must accurately keep time, even when the device is powered off because, it is often used as a trigger for turning the device on or triggering events such as alarm clocks. RTC ICs run on an alternate power source, which allows it to continually operate under low power or even when the computer is turned off. ICs on older systems utilize lithium batteries, whereas newer systems make use of auxiliary batteries or supercapacitors. RTC ICs that use supercapacitors are rechargeable and can be soldered. But in most consumer-grade motherboards, the RTC is powered by a single battery that, when removed, resets the RTC to its starting point.

RTC ICs regulate time with the use of a crystal oscillator and do not rely on clock signals like most hardware clocks. Aside from being responsible for the timing function of the system and its clock, RTC ICs ensure that all processes occurring in the system are appropriately synchronized. Although some may argue that this is a job for the system clock, the system clock is actually dependent on the RTC, making the RTC indirectly responsible for synchronization.

An RTC battery should last for three to five years or more. RTCs are essential; if the battery fails, it must be replaced to ensure continued operation. A dead battery can be diagnosed with an error message at startup or if the user finds that the clock or the setup configuration has become corrupted, flaky or odd.

Benefits of RTCs include:

  • RTC ICs have proved to be more precise than other methods — like programming the timer of the controller.
  • It frees the main system from time-critical tasks.
  • It has low power consumption and improved frequency stability.

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