The Real time clock DS1307 IC basically is stand alone time clock. Well, basically we can use a micrcontroller to keep time, but the value would go off as soon as it is powered off.
The RTC DS1307 is a handy solution to keep time all the way, when it is powered by a coin cell.
http://exploreembedded.com/wiki/index.php?title=A6.8051_Interfacing:_RTC_DS1307
