Real-time clocks (RTCs) are special types of clock and timing circuits that are used to keep track of the current time and date. They typically include a crystal oscillator that provides a stable reference frequency, and a counter or digital logic circuit that counts the number of oscillations and converts it into a time and date format.
RTCs are often used in applications where accurate timekeeping is critical, such as in computers, servers, and other digital systems. They can also be used in stand-alone devices such as alarm clocks and calendar clocks. Unlike regular clocks, which need to be reset manually or after a power outage, RTCs are able to maintain the correct time even when the power is off, thanks to a built-in battery or other backup power source.