A usb flash drives is a NAND-type flash memory data storage device integrated with a USB (universal serial bus) connector. USB flash drives are typically removable and rewritable, much shorter than a floppy disk (1-4 inches or 25-102 mm), and weigh less than 2 ounces (56g). Storage capacities range from 64MB to 32GB or more. Some allow 1 million write or erase cycles and have 10-year data retention, connected by USB 1.1 or USB 2.0 or both. USB Memory card readers are also available, whereby rather than being built-in, the memory is a removable flash memory card housed in what is otherwise a regular USB flash drive, as described below.
USB flash drives offer potential advantages over other portable storage devices, particularly the floppy disk. They are more compact, faster, hold more data, are more reliable for lack of moving parts, and have a more durable design. Additionally, it has become increasingly common for computers to ship without floppy disk drives. USB ports, on the other hand, appear on almost every current mainstream PC and laptop. These types of drives use the USB mass storage standard, supported natively by modern operating systems such as Windows, Mac OS X, Linux, and other Unix-like systems.
With nothing being mechanically driven in a flash drive, the name is something of a misnomer. It is called a “drive” because it appears to the computer operating system (and the user) in a manner identical to a mechanical disk drive, and is accessed in the same way.
A flash drive consists of a small printed circuit board typically in a plastic or metal casing and more recently in rubber casings to increase their robustness. This makes the drive sturdy enough to be carried about in a pocket, for example as a key fob, or on a lanyard. Only the USB connector protrudes, and it is typically protected either by a removable cap or by retracting into the body of the drive. Most flash drives use a standard type-A USB connection allowing them to be connected directly to a port on a personal computer.
To access the data stored in a flash drive, the drive must be connected to a USB port, either a host controller built into a computer, a USB hub, or some other device designed to access the data, such as an mp3 player with a USB-in port. Flash drives are active only when plugged into a USB connection and draw all necessary power from the supply provided by that connection. Some flash drives, however, especially high-speed drives, may require more power than the limited amount provided by a bus-powered USB hub, such as those built into some computer keyboards or monitors. These drives will not work unless plugged directly into a host controller (i.e., the ports found on the computer itself) or a self-powered hub.