Because flash memory lifespan depreciates faster than other storage devices, specifically designed flash file systems are used to extend that life by managing read and write operations different than would be for other storage. Technically this is achieved through the use of a memory technology device (MTD) layer. The MTD provides the abstraction layer between applications and hardware drivers. Through this, when flash storage is updated, a fresh block is written over, and file pointers are remapped to accommodate the change in data. At a later time, when memory management determines that it is most economical, it will then rewrite over older used blocks. Essentially, fresh flash memory will become full before rewrites are considered in an attempt to help extend life. This wear leveling method, however, does not apply to flash memory found in most popular removable devices, such as USB sticks, MMCs, SD cards, and CompactFlash memory, and instead these devices use a flash translation layer (FTL) and block storage. FTL metadata is stored in the flash space. The risk this poses is that the portions of memory that the mapping table resides on may wear out before the rest of the device. This risk is less so for enterprise flash storage which takes measures to ensure mapping tables are protected from wear, such as by allocating extra space for spares.