Some manufacturers deploy physical authentication tokens in the form of a flash drive. These are used to control access to a sensitive system by containing encryption keys or, more commonly, communicating with security software on the target machine. The system is designed so the target machine will not operate except when the flash drive device is plugged into it. Some of these "PC lock" devices also function as normal flash drives when plugged into other machines.
If you are taking your data to the extreme ends of the Earth and need to go a step above and beyond to keep it safe, the rugged Corsair Flash Survivor Stealth 64-bit is the drive for you. Constructed with aircraft-grade aluminum housing and outfitted with a molded shock damping collar, this drive is meant to survive anything you can throw at it. It can even be submerged in up to 200 meters of water because of the EPDM (ethylene propylene diene monomer rubber) waterproof seal. With speeds at around 85 MB/s, this isn’t the fastest drive around, but its ruggedness is unparalleled.
Universal Disk Format (UDF) version 1.50 and above has facilities to support rewritable discs like sparing tables and virtual allocation tables, spreading usage over the entire surface of a disc and maximising life, but many older operating systems do not support this format. Packet-writing utilities such as DirectCD and InCD are available but produce discs that are not universally readable (although based on the UDF standard). The Mount Rainier standard addresses this shortcoming in CD-RW media by running the older file systems on top of it and performing defect management for those standards, but it requires support from both the CD/DVD burner and the operating system. Many drives made today do not support Mount Rainier, and many older operating systems such as Windows XP and below, and Linux kernels older than 2.6.2, do not support it (later versions do). Essentially CDs/DVDs are a good way to record a great deal of information cheaply and have the advantage of being readable by most standalone players, but they are poor at making ongoing small changes to a large collection of information. Flash drives' ability to do this is their major advantage over optical media.