What is real time clock ?

Real time clock or RTC is a clock which shows the time in relation to a particular date and time. It is a very important feature of your mobile or tablet, as it enables you to set the correct time and date for any appointment or task. The RTC usually consists of a battery-backed clock chip or an atomic clock. The RTC is usually built-in the mobile or tablet but can be added as an accessory. So, when do you need real time clock ?