A USB flash drive, also variously known as a USB drive, USB stick, thumb drive, pen drive, flash-disk, or USB memory, is a data storage device that includes flash memory with an integrated USB interface. USB flash drives are typically removable and rewritable, and physically much smaller than an optical disc. Most weigh less than 30 grams (1.1 oz). Since first appearing on the market in late 2000, as with virtually all computer memory devices, storage capacities have risen while prices have dropped. As of March 2016, flash drives with anywhere from 8 to 256 GB are frequently sold, and less frequently 512 GB and 1 TB units. Storage capacities as large as 2 TB are planned, with steady improvements in size and price per capacity expected. Some allow up to 100,000 write/erase cycles, depending on the exact type of memory chip used, and have a 10-year shelf storage time.