USB 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 6 megabytes up to 64 gigabytes, limited only by current flash memory densities. As capacity increases, so does price.
USB flash drives have several advantages over other portable storage devices, particularly the floppy disk. They are generally faster, hold more data, and are considered more reliable (due to their higher resistance to electromagnetic interference) than floppy disks. These types of drives use the USB mass storage standard, supported natively by operating systems such as Linux (since the 2.4 kernel series), Mac OS X, Mac OS 9, Windows XP, Windows 2000 and Windows Me.
Microsoft Windows 95 OSR2.1 through Windows 98 SE do not natively support USB mass storage devices, though they do support USB. In order to use a USB flash drive with these versions of Microsoft Windows, a driver from the manufacturer must be installed. These drivers are generally available for Windows 98. Windows 95 OSR2.1A cannot support usb flash drives, though windows 95 OSR2.1B and above has some limited support. Mac OS 8.5.1 to Mac OS 9 supports USB mass storage devices through the use of an optional driver.
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. Some small drives have been made with a thin plug designed to mate with a standard USB port, but these are very rare.
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. Some drives need most of the power a standard USB port can supply, and therefore cannot be used with a bus powered hub.