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Apple Time Machine provides users with an intuitive incremental backup system for restoring files at a later date. Upon connecting an external USB or FireWire drive to your OS X machine Time Machine prompts you to set up the drive for backups. Thereafter backup 'snapshots' are taken hourly. Of course this is configurable with the following entry via Terminal:

sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto
     StartInterval
     -int 1800

The value at the end, in this case 1800, represents the number of seconds between backups (with 1 hour = 3600 seconds)