In general, any storage device that can be attached to a computer through a USB port. The term is particularly used for small portable storage devices typically sealed in plastic. Their physical size is reflected in the various names for this type of device – thumb drive, pen drive, keyring drive, memory stick. They have capacities as high as 4 gigabytes and on most modern personal computers they can be recognized as an additional drive without the need for a special driver. Storage devices of this type are increasingly used for backup, data transfer, storage of photographs or MP3 files, etc.