OS X recovery is built right into OS X. It allows you to repair or reinstall OS X from a USB drive without the need of a physical disk.
The OS X Recovery Disk Assistant allows you to create OS X Recovery on an additional drive. It has all the same capabilities as the built in OS X Recovery: reinstall Lion/Mountain Lion, repair the disk with Disk Utility, restore a Time Machine backup, and browse the web using Safari
Note: To create an external OS X Recovery with the OS X Recovery Assistant, a Mac must have an existing Recovery HD.
Download the OS X Recovery Assistant application to create an external OS X Recovery. Start the OS X Recovery Disk Assistant application, insert an external drive, and then follow the on-screen instructions.
The OS X Recovery Disk Assistant will complete, and the new partition won't be visible in Disk Utility or Finder. You can access OS X Recovery by rebooting the computer and holding the Option key. Select Recovery HD in the Startup Manager.