Backup

• There are many different means and methods online for creating a bootable USB thumb drive. The majority of these involve formatting the thumb drive. So before doing anything else, it is suggested that you back up any and all data on the thumb drive you wish to make bootable. If you forget to do this, you will irretrievably lose any and all data you had stored.
  
  

Purpose

• Before deciding on what route you wish to take in making your thumb drive bootable, decide exactly what it is you wish to accomplish with being able to boot via USB. Will you be making a drive filled with diagnostic and repair utilities? Do you need to boot to a preinstalled environment? Are you looking to be able to boot the PC and install an entire OS from the thumb drive? Each of these possibilities requires a different type of setup and different files for the setup. It also dictates the size of the thumb drive you will need to use.
  
  

Software and Partitioning

• In the end, a partition is really just a section of the disk. Thumb drives come preformatted as a single nonactive FAT32 partition of the full size of the drive, such as 4GB, 8GB or 16GB. So creating a bootable partition on a USB drive is really just a matter of making the drive active and installing the proper boot files in the proper way. Every utility available that makes your thumb drive bootable is in fact creating a boot partition by deleting the old partition, re-creating it as an active partition and then installing the necessary boot files.