well i have learned a lot about this subject today.the chain was replaced only.i could have sworn i ordered two chains so when the time came i could switch them out and keep rolling.i know that was what i wanted and would have done but its been over a year so i am not going to say that was what happened.the bike is a specialised rockhopper that was bought new with a sram cassette and sram crankset.i still have them on the shelf.i upgraded to better sram parts.so if my memory has failed me it came from the factory with sram parts and a kmc chain.if not i got the old switcharoo.i have got to start writing this stuff down when it happens.i never knew getting old could get this complacated!thanks guys.