A real-time clock (RTC) is a device combining a clock used in a computer, usually consists of a processor chipis specialized for this function counts the real time (year, month, day, hour , minute and second) even when the computer is turned off. It is used in many types of computers and is present in all modern PC. L 'RTC is also present in many embedded systems.
Some models of reality-Time clock circuits are integrated on the Maxim DS1307 and PCF8563 of Philips.
In order to maintain a count of the time your computer is off, the Real-time clock has a quartz oscillator dedicated to them and are powered by special lithium ion battery as opposed to general computer. In contrast, the clock that are not real-time do not work when the computer is off.
The RTC should not be confused with the real-time or the clock of the CPU.