1. If a bootable backup is part of your backup strategy, make sure you can actually boot from it.

2. Most modern operating systems enable you to build a bootable disk on removable media.

3. To do a clean install, you will need bootable media.

4. Obviously, then, you want to create your bootable install drive using the latest version of the Mavericks installer.

5. Connect to your Mac the properly formatted hard drive or flash drive you want to use for your bootable Yosemite installer.

6. Connect to your Mac the properly formatted hard drive or flash drive you want to use for your bootable Mavericks installer.

7. Also, if your Mac is experiencing problems, a bootable install drive makes a handy emergency disk.

8. If the destination drive has additional partitions, just drag the partition you want to use as your bootable installer volume.

9. All provide a bootable CD version as well.