My clock keeps resetting itself when i reboot my mikrotik from the telnet or winbox. Then it is back to 1970/01/01. Then i have to set the time again. What can this be? Does mikrotik have a onboard flash memory ot battery that keeps the time and the data. thanx

No. On the routerboards there are no batteries (yet). Maybe in the next versions they will put it. You can setup the NTP client though so it synchronizes with one of the NTP servers on the web, every time your router starts.