Disk Utility - What is it?

Installed by default on all Mac OS X from X.3 and up, it performs disk-related tasks:

• creation, conversion, compression or encryption
• mounting, unmounting and ejecting
• repairing a disk if its damaged
• verifying and repairing permissions
• erasing, formatting, partitioning and cloning
• secure deletion based on DOD standards
• restoring volumes
• burning, erasing discs
• checking the S.M.A.R.T. status of a hard disk

Its available from the command line as diskutil but is more often recognized in the Macintosh HD > Applications > Utility Folder.