The Scan Disk utility works to preserve data integrity of your hard drive. Your files are stored on your hard drive in data groups called "clusters", sometimes these clusters can become "cross linked" with other clusters belonging to other files, or they can simply become "lost" from the rest of its fellow clusters. When you run scan disk the utility saves the "lost" file fragments into new files that you can view called "check" files (*.chk). It also repairs cross-linked clusters by making a copy and pairing it to two separate families (the original and the cross linked one).
Tip 1: Run the Scan Disk Utility Once a Month.With the use of your files and programs over time, they tend to move location on your hard disk. Sometimes the individual clusters that make up a single file can become separated (fragmented). With increased fragmentation comes weaker performance of your computer, because it takes longer for your processor to access a single file. The longer and harder your processor must work the shorter the life of your computer. The Defrag utility corrects the problem of separated file fragments, by placing all of the data clusters that belong together next to each other.
Tip 1: Run the Defrag Disk Utility Once a Month.