USB flash drive
 
A USB drive, shown with a 24 mm U.S. quarter coin for scale.
Flash drive with retractable USB ConnectorUSB flash drives are NAND-type flash memory data storage devices integrated with a USB interface. They are typically small, lightweight, removable and rewritable. Memory capacity typically ranges from 128 megabytes up to 64 gigabytes, limited only by current flash memory densities, although cost per megabyte increases rapidly at higher capacities due to the expensive components. For example, as of October 2006, flash drives were available in retail stores at US$25 for 512MiB, US$35 for 1GiB, US$60 for 2GiB, US$100 for 4GiB, and US$160 for 8GiB.
  USB flash drives have several advantages over other portable storage devices, particularly the floppy disk. They are more compact, generally faster, hold more data, and are considered more reliable (due to their lack of moving parts) than floppy disks. These types of drives use the USB mass storage standard, supported natively by modern operating systems such as Linux, Mac OS X, and Windows.
  A flash drive consists of a small printed circuit board encased in a robust plastic or metal casing, making the drive sturdy enough to be carried about in a pocket, as a keyfob, or on a lanyard. Only the USB connector protrudes from this protection, and is usually covered by a removable cap. Most flash drives use a standard type-A USB connection allowing them to be connected directly to a port on a personal computer.
  Most flash drives are active only when powered by a USB computer connection, and require no other external power source or battery power source; they are powered using the limited supply afforded by the USB connection. To access the data stored in a flash drive, the flash drive must be connected to a computer, either by direct connection to the computer's USB port or via a USB hub.
  

History

An original 16 megabyte “disgo”; The 8 MB version is considered to be the first USB flash driveThe flash drive was first invented in 1998 by Dov Moran, President and CEO of M-Systems Flash Pioneers (Israel). Dan Harkabi, who is now a Vice President at SanDisk, led the development and marketing team at M-Systems. His most significant contribution was that the product be self-reliant and free of the need to install drivers. Nearly simultaneous development of similar products was undertaken at Netac and at Trek 2000, Ltd. All three companies have similar and disputed patents. IBM was the first North American seller of a USB flash drive, and marketed an 8 MB version of the product in 2001 under the “Memory Key” moniker. IBM later introduced a 16 MB version manufactured by Trek 2000, and returned to M-Systems for the 64 MB version in 2003. Lexar can also lay claim to a USB flash drive product. In 2000 they introduced a Compact Flash (CF) card having an internal USB function. Lexar offered a companion card reader and USB cable that eliminated the need for a USB hub. 
The first flash drives were made by M-Systems and distributed in Europe under the “disgo” brand in sizes of 8 MB, 16 MB, 32 MB, and 64 MB. These were marketed as “a true floppy-killer”, and this design was continued up to 256 MB. Asian manufacturers soon started making their own flash drives that were cheaper than the Disgo series. 
Modern flash drives have USB 2.0 connectivity. However, they do not currently use the full 480 Mbit/s the specification supports due to technical limitations inherent in NAND flash.
Flash drives have become iconic as a sort of “fashion statement”, much like the iPod's white ear bud headphones.
   

[source:’wikipedia’]