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corrected for flash drive

A USB drive, shown with a 24 mm US quarter coin for scale.

A USB flash drive is essentially NAND-type flash memory integrated with a USB 1.1 or 2.0 interface used as a small, lightweight, removable data storage device of up to 16 GB (as of 2006). USB flash drives use the USB mass storage standard for removable storage devices. To use such a device, your operating system must have driver support for both USB mass storage plus the file system used on the flash drive. Microsoft Windows ships with driver support for USB mass storage since Windows Millennium Edition and Windows 2000. Windows 98 did not ship with USB mass storage support, so a driver supplied by the vendor of the flash drive is required.

USB flash drives are also known as "pen drives", "chip sticks", "thumb drives", "flash drives", "USB keys", and a wide variety of other names. They are also sometimes erroneously called memory sticks, which is a Sony trademark describing their proprietary memory card system.

A flash drive consists of a small printed circuit board encased in a robust plastic[1] or metal casing[2], 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 feature the 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[3] but these are very rare.

Flash drives are active only when powered by a USB computer connection, and require no other external power source or battery power source; key drives are run off the limited supply afforded by the USB connection (5 volts and up to 500 mA). 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 need most of the power a standard USB port can supply and therefore cannot be used with a bus powered hub.

History

The flash drive was first invented in 1998 at IBM as a floppy drive replacement for the ThinkPad line of products. Although there is an IBM disclosure, they did not patent it. IBM later contracted M-Systems to develop and manufacture it non-exclusively. M-Systems holds the patent to this device, as well as a few other related patents.

The first flash drives were made by M-Systems under the "disgo" [4] brand in the following sizes: 8MB, 16MB, 32MB & 64MB. These were marketed as "a true floppy-killer," and this design was continued up to 256MB. Asian manufacturers soon started making their own flash drives cheaper than the Disgo series.

Modern flash drives have USB 2.0 connectivity. However, they do not currently use the full 480Mbit/s the specification supports due to technical limitations.

Although originally conceived for individuals to share data, today's flash drives are becoming more than utilitarian in nature. Like iPods in the ear, a flash drive around the neck with a lanyard has become a fashion statement.

Components

This photograph shows both sides of the printed circuit board (PCB) inside a typical flash drive (circa 2004). The flash drive in this photograph is a 64 MB USB 2.0 device with its plastic case removed.

One end of the device is fitted with a single male type-A USB connector. Inside the plastic casing is a small, highly cost-engineered, 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

The parts of a typical flash drive are as follows:

• Male type-A USB connector - provides an interface to the host computer. (item 1 in the diagram)
• USB mass storage controller - implements the USB host controller and provides a seamless linear interface to block-oriented serial flash devices while hiding the complexities of block-orientation, block erasure, and wear balancing. The controller contains a small RISC microprocessor and a small amount of on-chip ROM and RAM. (item 2 in the diagram)
• A NAND flash memory chip - stores data. NAND flash is typically also used in digital cameras. (item 4 in the diagram)
• Crystal oscillator - produces the device's main 12 MHz clock signal and controls the device's data output through a phase-locked loop (the crystal itself is item 5 in the diagram)

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. (item 3 in the diagram)
• LEDs - indicates data transfers or data reads and writes. (item 6 in the diagram)
• Write-protect switch - indicates whether the device should be in "write-protection" mode. (item 7 in the diagram)
• Unpopulated space - provides space to include a second memory chip. Having this second space allows the manufacturer to develop only one PCB that can be used for more than one storage size device, to meet the needs of the market. (item 8 in the diagram)
• USB connector cover or cap - reduces the risk of damage due to static electricity, 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. However, this increases the risk of the device being lost during transport. For this reason, most devices now have the hole on the main device body, though this requires the entire keychain to be attached to the computer. Some, therefore, have holes in both places.

Strengths and weaknesses

Flash drives are impervious to the scratches and dust that plagued previous forms of portable storage like compact discs and floppy disks, and their durable solid-state design means they often survive casual abuse (impacts, being dropped or crushed, run through a washing machine, or even dropped in coffee). This makes them ideal for transporting personal data or work files from one location to another (such as from home to school or office) or for carrying around personal data that the user typically wants to access in a variety of places. The near-ubiquity of USB support on modern computers means that such a drive will work in most places. However, Windows 98 does not support generic USB mass storage devices out of the box; a separate driver for each manufacturer's USB drive used on the machine must be installed. Versions of Windows 95 with USB support are even worse, with drivers being almost totally unavailable.

Flash drives are also a relatively dense form of storage - even the cheapest will store dozens of floppy disks worth of data, and a moderately priced one can hold as much data as a CD or more. Historically, flash drive capacity has ranged from a few megabytes in size up to a few gigabytes. In 2003, most flash drives ran at the USB 1.0/1.1 speeds of 1.5 Mbit/s or 12 Mbit/s. 2004 saw the release of newer flash drives featuring USB 2.0 interfaces. Although USB 2.0 can deliver 480 Mbit/s, these flash drives are limited by the bandwidth of the underlying flash memory device, with maximum read speeds of around 100 Mbit/s and write speeds a little slower. In ideal conditions, the flash memory in the drives can retain data for 10 years.

Flash drives implement the USB mass storage device class, meaning that most modern operating systems can read and write to flash drives without any additional device drivers. Instead of exposing the complex technical detail of the underlying flash memory devices, the flash drives export a simple block-structured logical unit to the host operating system. The OS can use whatever type of filesystem or block addressing scheme it wants. Some computers have the ability to boot up from flash drives, but that capability must be supported in the computer's BIOS, and (like other mass storage devices) the flash drive must be set up to do so and loaded with a bootable disk image (rather than a conventional filesystem image).

Like all flash memory devices, flash drives can sustain only a limited number of write/erase cycles before failure. In normal use, mid-range flash drives currently on the market will support several million cycles, although write operations will gradually slow as the device ages. This should be a consideration when using a flash drive as a hard drive to run application software or an operating system. To address this (and the space limitations common on flash drives), some developers have produced versions of operating systems (such as Linux) or commonplace applications (such as Mozilla Firefox) designed to run from flash drives. These are typically optimized for size and set up so as to place temporary or intermediate files in memory rather than nonvolatile storage (to avoid excessive writing to the flash memory in the flash drive).

A few cheaper USB flash drives have been found to use unsuitable flash memory chips labelled as 'ROM USE ONLY' - these are intended for tasks such as Flash BIOS for Routers rather than for continual rewrite use, and fail after a very small number of cycles. [5]

When compared to a floppy drive, most USB flash drives do not employ a write-protect mechanism. Such a switch on the housing of the drive itself would keep the host computer from writing or modifying data on the drive. A write-protect switch would make the devices suitable for repairing virus contaminated host computers without infecting the USB flash drive itself.

Flash drives are more tolerant of abuse than mechanical drives, but can still be damaged or have data corrupted if impact loosens circuit connections.

Size and style of packaging

When selecting a flash drive for purchase, the size and shape of the casing should be considered. Some manufacturers, in an attempt to differentiate themselves, use a stylised and bulky shell which may not allow the flash drive to be inserted into some USB ports, due to limited space around the port. This is particularly an issue with laptops or computers with front USB ports that are deeply recessed (or too close to neighboring ports that are also in use). Most manufacturers supply a USB extension cable (sometimes a slim one, sometimes a normal thick one) to work around this problem, but this is far less convenient to carry around than just the flash drive itself.

Common uses

Network 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. The external write protect switch on some flash drives is particularly useful, as it allows the system administrator to plug a flash drive containing anti-virus, spyware-removal, or trouble diagnosis software into a suspect machine without risking the transmission of a virus or worm.

Flash drive for applications

Flash drives are used to carry applications that run on the host computer without requiring installation. The Mozilla Firefox browser has a configuration for flash drives. 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.

Flash drives as audio players

Many companies make solid-state digital audio players (MP3 players) in a small form factor, essentially producing flash drives with sound output and a simple user interface. The most successful of these have been Apple Computer's iPod shuffle, iPod nano and the Creative Labs MuVo.

Flash drives to boot operating systems

In a way similar to that used in LiveCD, one can launch Linux and other Unix distributions from a bootable flash drive.

Security

Some flash drives feature encryption of the data stored on them, generally using an encrypted filesystem rather than a conventional one. This prevents an unauthorized person (who has found or stolen the drive) from accessing confidential data stored on it. The disadvantage of this is that the drive is accessible only in the minority of computers which have the same encryption software (for which no portable standard is widely deployed) unless the encryption software is stored unencrypted on the drive, and the user must carry the (large, and frequently impossible-to-remember) cryptographic key around by some other means.

Some encryption applications (such as TrueCrypt, CryptoBuddy, and Private Disk) allow running without installation. The executable files can be stored on the USB drive, together with the encrypted file-image. The encrypted partition can be accessed on any computer running Microsoft Windows. The newer Lexar JumpDrive Secureallows the user to configure secure and public partitions of different sizes. Executable files for Windows, Macintosh, and Linux are usually included on the drive.

Newer flash drives support biometric fingerprinting to confirm the user's identity. As of mid-2005, this was a relatively costly alternative to standard password protection offered on many new USB flash storage devices.

Some manufacturers deploy physical authentication tokens in the form of a flash drive. These are used to control access to a sensitive system by containing encryption keys or (more commonly) communicating with security software on the target machine. The system is designed so the target machine will not operate except when the flash drive device is plugged into it. Some of these "PC lock" devices also function as normal flash drives when plugged into other machines.

Flash drives present a significant security challenge for large organizations. Their small size and ease of use allows unsupervised visitors or unscrupulous employees to smuggle confidential data out with little chance of detection. Equally, corporate and public computers alike are vulnerable to attackers connecting a flash drive to a free USB port and uploading hacking software such as rootkits or packet sniffers. To prevent this some organizations (particularly government departments and larger corporations) forbid the use of flash drives, and some computers are configured to disable the mounting of USB mass storage devices by ordinary users (a feature found only belatedly on Windows XP, being introduced only in its second service pack). In a lower-tech security solution, some organizations disconnect USB ports inside the computer or fill the USB sockets with epoxy. It is very difficult to get vendor ID and Product ID of the USB drives used in a computer. Some system administrators use Devicelock software to control usb usages.

Naming confusion

No commonly recognized term for these devices has emerged. The resulting confusion makes them more difficult for manufacturers to market and for consumers to research. This problem may have slowed the adoption of this technology.

All of the following names (optionally prefixed with "USB") have been used:

• bug - perhaps a reference to the size and appearance of some USB drives
• chingadera - primarily in Mexican Spanish - may carry a vulgar connotation
• chip stick
• chubidubi - primarily in Cuban Spanish
• Cruzer - a SanDisk brand name
• data stick
• data key
• disk on key
• dongle - regarded by some as an inaccurate use of this word
• doofer - Commonly used in Northern Ireland. Is also used to describe various small electronic devices (Almost always prefixed with "USB").
• finger drive
• flash disk
• flash drive
• flash memory drive
• gigachip
• geek stick - used by Geek Squad agents to refer to the special-use, branded USB flash drives with special diagnostic tools pre-loaded onto them.
• gli-gli - used in Andalusia, Spain
• jump drive - a trademarked name used by Lexar
• jump stick
• key
• keychain drive
• keydrive
• keyfob - widely used in the Seattle area
• magic key
• magic stick - common in some Ohio towns
• memory drive
• memory key
• memory stick - inaccurate use of a Sony trademark (Memory Stick, capitalized) for a non-USB proprietary flash memory module
• micro hard drive
• mobile drive
• nerd bling
• nerd necklace - used when worn around the neck
• nerd stick - uncommon term
• pen drive
• piripicho (primarily in South American Spanish)
• pocket drive
• stick
• thumb drive
• thumb key
• travel drive - a Memorex trademark
• travel stick
• USB - sometimes used as a shorthand
• vault drive - Sony's USB storage devices started using this name in March 2005
• USB drive
• USB Stick

Comparison to other portable memory forms

Flash storage devices are best compared to other common, portable, swappable data storage devices: floppy disks, Zip disks, and CD-R/CD-RW discs. 3.5 inch floppy disks and Iomega Zip disks are still available as of late 2005, despite their declining popularity. While for many purposes it would be ideal to transport files between computers wirelessly, not all computers are equipped with wireless cards, and networks are not readily available.

Floppy disks were the first publicly-popular method of file transport, but have essentially become obsolete due to their low capacity (1.44 MB) and relatively low speed. Virtually all new computers include USB ports, and many of them are now sold without a floppy drive (the Apple iMac being the first to ship this way). Floppy disks are still in use because of their low cost and ease of use with older systems (particularly Windows 98, which is still fairly common and cannot support USB flash drives without extra drivers). Attempts to extend the floppy standard (such as the Imation SuperDisk) were not successful because of a reputation for unreliablity and the lack of a single standard for PC vendors to adopt.

The Iomega Zip drive enjoyed some popularity, but never reached the point of ubiquity in computers. Also, the larger sizes of Zip (now up to 750MB) cannot be read on older drives. Therefore, unless one were to carry around an external drive (and possibly drivers, cables, etc.), their usefulness as a means of moving data was rather limited. The cost per megabyte was fairly high (though admittedly cheaper than flash), with individual disks often priced at $10 USD or higher. Because the material used for creating the storage medium in Zip disks is similar to that used in floppy disks, Zip disks have a higher risk of failure (such as the click of death) and data loss. Larger removable storage media, like Iomega's Jaz drive, had even higher costs (both in drives and in media), and as such were never really feasible as a floppy alternative.

CD-R and CD-RW are swappable storage media alternatives. Unlike Zip and floppy drives, DVD and CD recorders are increasingly common in personal computer systems. CD-Rs can only be written to once (unless one creates multiple sessions, which cannot be read by some old CD-ROM drives), and the more expensive CD-RWs are only rated up to 1,000 erase/write cycles, whereas modern NAND-based flash drives often last for 500,000 or more erase/write cycles. Optical storage devices are also usually slower than their flash-based counterparts. Compact discs with an 11.5 cm diameter can also be inconveniently large and, unlike flash drives, cannot fit into a pocket or hang from a keychain. Smaller CDs are available; these are an exception. There is also no standard file system for rewriteable optical media; packet-writing utilities like DirectCD and InCD exist, but produce discs that are not universally readable, despite claiming to be based on the UDF standard. The upcoming Mount Rainier standard addresses this shortcoming in CD-RW media, but is still not supported by most DVD and CD recorders or major operating systems.

Flash storage devices, compared to other storage media, are fast, high-capacity, durable, and compact. Also, traditional removable media cannot make incremental improvements due to the need for drive/disk compatibility, instead improving in infrequent but large steps. Since flash drives have a generic USB interface (and no user separable parts beyond it), manufacturers can use technical improvements (such as larger and faster flash memory chips or controllers) as soon as they are available without compromising backwards compatibility. Furthermore, unlike Zip and floppies, flash memory lacks moving parts, making it ideal as a simple solution, requiring only a port to interact with a system. The popularity of flash storage devices may be attributed to their compact size, operating system compatibility, and their use of the standard USB interface.

Future developments

Semiconductors corporations have striven to radically reduce the cost of the components in a flash drive by integrating various flash drive functions in a single chip, thereby reducing the part-count and overall package cost. As of 2004, some manufacturers plan to include more ICs so that the storage and logic/communications functions are packaged in a single ultra-low-cost device.

In efforts to focus on increasing capacities, 64 MB and smaller capacity flash memory has been largely discontinued, and 128 MB capacity flash memory is being phased out.

Lexar is attempting to introduce the USB Flash Card, which would be a compact USB flash drive intended to replace various kinds of flash memory cards.

Trivia

In 2004, the German punk band WIZO was the first artist to release music in MP3 format on a USB drive titled the "WIZO Stick-EP."

Poor quality knock-offs

Recently some manufacturers namely Goodmans and possibly other cheap flash drive manufacturers have been using low cost "ROM-only" chips in their drives instead of regular flash memory that is rated for use up to 100,000 write cycles. These cheap ROM-only chips will only last 5-10 cycles and are generally used for storing the Firmware in embedded devices.

See also

• List of portable applications
• USB Flash Drive Alliance
• Pocket hard drive
• Sneakernet
• Cfdisk

External links

Keydrive applications

• Bootdisk-Images - Bootdisks for using them on the USB-Drive
• USBApps - Listing of USB keydrive applications
• TinyApps - Tiny applications for your USB keydrive
• Sony Apps - Sony applications for your USB keydrive
• StandAlone - Stand alone applications for your USB keydrive
• airWRX - USB Keydrive application framework
• kikizas.net - Freeware programs to run from a USB stick
• Portable Freeware - The Portable Freeware Collection
• Portable Apps Collection - Large collection of portable apps available in one free download
• RUNT - ResNet Network Tester for USB Keydrives
• CryptoStick Software - Encryption, Private Internet Browsing, PestPatrol, all for your USB Device
• Dekart Private Disk - User-friendly disk encryption software for Windows XP/9x/2000 - AES 256 bit encryption
• Truecrypt - Free open-source disk encryption software for Windows XP/2000/2003
• KeePass Password Safe - Password management utility (use the ZIP version)
• Gaim - a multi-protocol instant messaging (IM) client for Linux, BSD, MacOS X, and Windows.
• Portable WXtrack - Portable Visual Satellite tracking software
• PortableApps.com
  • Portable AbiWord - The popular word processor AbiWord optimized for USB pen drive use
  • Portable Firefox - Web browser
  • Portable Thunderbird - Email
  • Portable Thunderbird with Enigmail and GPG - Email plus built in encryption
  • Portable Sunbird - Calendar application
  • Portable NVU - Complete Web Authoring System
  • Portable OpenOffice.org - Complete Office Suite
  • Portable Gaim - instant messaging made portable and secure.
• Web Server on a Stick Apache web server with Typo3 CMS, PHP and MySQL that runs entirely from a USB stick
• Portable CE Using the Windows CE emulator, you can have your entire "internet communications system" on a virtual machine on a USB keychain
• Faulty USB key from Goodmans

HOWTO pages

• Encrypted thumb drive and autoplay howto - Open source tools and a very clear walkthrough
• Combining encryption and mobility howto - A guide on using Portable Firefox, Thunderbird, Instant Messenger in a secure way

GNU/Linux distributions for USB

• Damn Small Linux (DSL), a small derivative of Knoppix, tailored to USB.
• Knoppix USB Based.
• Featherlinux - distribution specifically created for USB sticks
• Flash-Puppy a mature distro designed for keydrives
• Generic Howto on USB booting, incl. with using a floppy/CD for the initial boot if the BIOS does not support USB
• Installing Debian from a USB stick
• LiveDistro.org - Operating systems and HOWTOs for LiveUSBs
• Minimalistic SLAX versions
• USB on Linux

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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "flash drive".