Nissan Micra 1997 cambelt replacement query?

I have just bought a 1997 Nissan Micra with 59,000 on clock. have bben told you should replace cambelt at 50,000 miles, but then also been told is is not Cambelt but Cam chain that you need to replace at every 50,000 miles.

What is the difference? And what (if any) should I replace?

Chris Wild
January 2009