It's not unusual for a hard drive to experience problems. When problems occur on the main hard drive, it can produce lock ups and slower performance. Apple helps to solve this problem by letting you perform disk repairs to any drives with the exception of the start up drive. For example, you could use disk repair to fix problems on a damaged JAZZ drive, or a secondary hard drive. Apple's Disk Utility locates and fixes problems with catalog and storage files. When information in these areas is damaged, it can cause trouble opening files and slowing down performance.