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 8 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 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 XP.

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.

Components

One end of the device is fitted with a single male type-A USB connector. Inside the plastic casing is a small printed circuit board. Mounted on this board is some simple power circuitry and a small number of surface-mounted integrated circuits (ICs). Typically, one of these ICs provides an interface to the USB port, another drives the onboard memory, and the other is the flash memory.

Essential components

There are typically three parts to a flash drive:

• Male type-A USB connector - provides an interface to the host computer.

• USB mass storage controller - implements the USB host controller and provides a linear interface to block-oriented serial flash devices while hiding the complexities of block-orientation, block erasure, and wear balancing, or wear levelling, although drives that actually perform this in hardware are rare. The controller contains a small RISC microprocessor and a small amount of on-chip ROM and RAM.

• NAND flash memory chip - stores data. NAND flash is typically also used in digital cameras.

• Crystal oscillator - produces the device's main 12 MHz clock signal and controls the device's data output through a phase-locked loop.

Additional components

The typical device may also include:

• Jumpers and test pins - for testing during the flash drive's manufacturing or loading code into the microprocessor.

• LEDs - indicate data transfers or data reads and writes

• Write-protect switches - indicate whether the device should be in "write-protection" mode.

• Unpopulated space - provides space to include a second memory chip. Having this second space allows the manufacturer to develop only one printed circuit board that can be used for more than one storage size device, to meet the needs of the market.

• USB connector cover or cap - reduces the risk of damage due to static electricity, and improves overall device appearance. Some flash drives do not feature a cap, but instead have retractable USB connectors. Other flash drives have a "swivel" cap that is permanently connected to the drive itself and eliminates the chance of losing the cap.

• Transport aid - In some cases, the cap contains the hole suitable for connection to a key chain or lanyard or to otherwise aid transport and storage of the USB flash device.

Common uses

Personal data transport

The most common use of flash drives is by individuals to transport and store personal files such as documents, pictures and video.

Computer repair

Flash drives enjoy notable success in the field of PC repair as a means to transfer recovery and antivirus software to infected PCs, while allowing a portion of the hosts machines data to be backed up in case of emergency.

System administration

Flash drives are particularly popular among system and network administrators, who load them with configuration information and software used for system maintenance, troubleshooting, and recovery.

Application carriers

Flash drives are used to carry applications that run on the host computer without requiring installation. U3, backed by flash drive vendors, offers an API to flash drive-specific functions. airWRX is an application framework that runs from a flash drive and turns its PC host and other nearby PCs into a multi-screen, web-like work environment.

Audio players

Many companies make solid state digital audio players in a small form factor, essentially producing flash drives with sound output and a simple user interface. Probably the best-known of these has been Apple Computer's iPod shuffle, and the Creative Labs MuVo.

To boot operating systems

In a way similar to that used in LiveCD, one can launch any operating system from a bootable flash drive, known as a Live USB.

In arcades

In the arcade game In the Groove and more commonly In The Groove 2, flash drives are used to transfer high scores, screenshots, dance edits, and combos throughout sessions. While use of flash drives is common, the drive must be Linux compatible, causing problems for some players. Data used can then be uploaded to Groovestats

Src Wikipedia

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