Hai guys,Iam using win-XP(professional),whenever i start my computer it performs scan disk automatically,that too only for some drives,(eventhough I had shutdowned correctly).I thought it is problem of bad sectors, but my hard disk is a new one and i don't think there are any bad sectors.Is this some kind of virus?

Actually what are these bad sectors?How do they come?Is there any chance to prevent them from coming?