article

USB flash drives are NAND-type flash memory data storage devices integrated with a USB interface. They are typically small, lightweight, removable and rewritable. Sizes range from 8 megabytes to several gigabytes, although as capacity increases, price does as well.

USB flash drives are faster, hold more data, and are generally more reliable than floppy disks, which were previously the norm for portable storage. 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 but not for Windows 95. Mac OS 8.5.1 and up 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 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 [http://www.acp-ep.com/usb_keydrives20_photos.html" target="_blank" >*, 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.

History

The flash drive was first invented in 1998 by Dov Moran, President & 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 480Mbit/s the specification supports due to technical limitations inherent in NAND flash.

Thumb drives have become iconic as a sort of "fashion statement", much like the iPod's white ear bud headphones. *).

Components


The internal components of a typical flash drive
1 USB connector
2 USB mass storage controller device
3 Test points
4 Flash memory chip
5 Crystal oscillator
6 LED
7 Write-protect switch
8 Unpopulated space for second flash memory chip

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.

Strengths and weaknesses

Flash drives are nearly impervious to the scratches and dust that were problematic for previous forms of portable storage, such as compact discs and floppy disks, and their durable solid-state design means they often survive casual abuse. 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.

Flash drives are also a relatively dense form of storage, where even the cheapest will store dozens of floppy disks worth of data. Some can hold more data than a CD. Very high-end flash drives can even hold more data than a DVD.

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 operating system can use whatever type of filesystem or block addressing scheme it wants. Some computers have the ability to boot up from flash drives.

Like all flash memory devices, flash drives can sustain only a limited number of write and erase cycles before failure. Mid-range flash drives under normal conditions 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 to run application software or an operating system. To address this, as well as space limitations, some developers have produced special 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 configured to place temporary or intermediate files in memory rather than store them temporarily on 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 firmware for embedded devices rather than for continual rewrite use, and fail after a very small number of cycles. *

The FAT filesystem most commonly used on USB flash drives is subject to file fragmentation, much like magnetic storage devices. Excessive fragmentation on flash storage can have a negative impact on performance. *

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. Write-protection would make a device 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 an impact loosens circuit connections.

Size and style of packaging

Some manufacturers choose to incorporate form over function. Lexar's Jump Drives, in particular, are often bulky and difficult to connect to the USB port.

Common uses

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.

Flash drive for applications

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. The Mozilla Firefox browser has a configuration for flash drives, as does Opera (Opera@USB).

Flash drives as 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 most well known of these has been Apple Computer's iPod shuffle, and the Creative Labs MuVo.

Flash drives 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 LiveUSB.

Flash drives 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. *

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 from accessing the data stored on it. The disadvantage 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, the user must carry the large 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. Other flash drives allow 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 using malicious software such as rootkits or packet sniffers. To prevent this, some organizations 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 introduced in Windows XP service pack 2; others use third-party software to control USB usage. In a lower-tech security solution, some organizations disconnect USB ports inside the computer or fill the USB sockets with epoxy.

Etymology

No commonly recognized term has emerged. The resulting confusion makes them more difficult for manufacturers to market and for consumers to research.

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
  • Chip stick
  • Clip Drive
  • Clip Flash Drive
  • Data key
  • Data stick
  • Disk on key
  • Dongle - regarded by some as an inaccurate use of this word
  • Finger drive
  • Flash disk
  • Flash drive
  • Flash memory drive
  • Geek stick - used by Geek Squad agents to refer to the special-use, branded USB flash drives with special diagnostic tools pre-loaded
  • Gigachip
  • 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 - not to be confused with the Sony Memory Stick
  • Micro hard drive
  • Mobile drive
  • Nerd bling
  • Nerd necklace - used when worn around the neck
  • Nerd stick
  • Pen - also used in much of Portugal
  • Pen drive
  • Pocket drive
  • Stick
  • Thumb drive
  • Thumb key
  • Travel stick
  • USB disk/disc
  • USB drive
  • USB key
  • USB Pen
  • USB Stick
  • USB - sometimes used as a shorthand
  • USB zip drive

Localised names

  • Chiave USB - used in Italy
  • Chubidubi or Llave or Memoria - primarily in Cuban Spanish
  • Doofer - Commonly used in Northern Ireland. Is also used to describe various small electronic devices (almost always prefixed with "USB").
  • flasaki ("little flash"), in Greece
  • flashaya, used in Egypt
  • Flashka (флэшка) - used in Russian
  • Fleška - used in Slovakia
  • Gli-gli - used in Andalusia, Spain
  • Jon - mainly used in Doylestown, Pennsylvania
  • Maya Key - primarily in Costa Rican Spanish
  • Memoria USB or simply USB - primarily in Mexican Spanish
  • Pendrajw - used in Poland
  • Pene - used in some of the Canary Islands, Spain
  • Piripicho (primarily in South American Spanish)
  • Stick Drive - Commonly used in Klamath Falls, Oregon
  • Sticky - sometimes used in the Netherlands
  • U-disk - Commonly used within the Chinese/Asian Community
  • USB-minne "USB memory", used in Norway and Sweden
  • USB-minni "USB memory", used in Iceland
  • USB-nøkkel "USB key", used in Norway
  • USB-pinne a (bad) translation of "USB Stick" used by some manufacturers in Norway and Sweden.
  • USB Stick or just Stick in German

Brand names

  • Attaché - a PNY trademark
  • Cruzer - a SanDisk trademark
  • Data Traveler - a Kingston trademark
  • Disgo - a Disgo trademark
  • FlashDisc - a brand of low-density flash drives introduced by Memorex
  • Intelligent Stick - a PQI trademark
  • JetFlash - a Transcend trademark
  • JumpDrive - a Lexar trademark
  • Memory stick - inaccurate use of a Sony trademark (Memory Stick, capitalized) for a non-USB proprietary flash memory module
  • Micro Vault - a Sony trademark
  • Thumbdrive a Trek 2000 International Ltd trademark
  • TravelDrive - a Memorex trademark
  • Super stick - Kingmax's small flash drive. *
  • MyFlash - trademark of A-Data
  • Max Drive/Evo Drive - a Datel trademark, primarily for use with their video game console peripherals, but usable as standard flash drives
  • Relay - a Staples, Inc trademark.
  • ToughDrive - an ATP, Inc trademark Rugged, waterproof and vary fast.

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 mid-2006, 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, low speed, and low durability. 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. 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. Unless one were to carry around an external drive, their usefulness as a means of moving data was rather limited. The cost per megabyte was fairly high, 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 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 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, 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, and 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.

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. Kanguru has recently released a 64 GB flash memory drive that utilizes USB 2.0 and claims 10 years worth of information writing. *

Lexar is attempting to introduce a USB Flash Card [http://www.lexar.com/ufc/, which would be a compact USB flash drive intended to replace various kinds of flash memory cards.

SanDisk has introduced a new technology to allow controlled storage and usage of copyrighted materials on flash drives, primarily for use by students. This technology is termed FlashCP.

Trivia

  • In 2004, the German punk band WIZO was the first musical group to release music in MP3 format on a USB drive, titled the WIZO Stick-EP. *
  • In the films The Recruit & Collateral, thumb drives play an important role in the plot.
  • Some flash drives can retain their memory after being submerged in water *, even through a (quite unintentional) machine wash.

See also

External links

Keydrive applications

Security

  • Dekart Private Disk - User-friendly disk encryption software for Windows XP/9x/2000
  • Truecrypt - Free open-source disk encryption software for linux and Windows XP/2000/2003
  • KeePass Password Safe - Password management utility (use the ZIP version). Requires Windows.
  • KeePassX Cross-platform Password Manager - Password management utility (GPL License).
  • WinEncrypt CryptArchiver - Creates 448 bit password protected encrypted virtual drives on the USB/Flash drive. Is bundled with some USB drives. Shareware, but free edition is available.
  • Defygo - Free encryption suite including password vault, random password generator, and file encryption. It also includes cryptograms and encrypted email driven by a buddy/pal system. Requires Windows 98 or higher.
  • Portable CE - An emulator for your USB, use your computer entirely from the USB thumb drive without affecting the computer being used.
  • PRO-Tector™ Flash USB Secure Drives - creates 'dongle-like' security on standard USB Flash or Thumb Drives.
  • AntiDuplicate - Transforms USB flash drives to software protection key dongles.

HOWTO pages

Computer storage devices | Solid-state computer storage media | USB

USB stick | USB flash disk | USB-nøgle | USB-Stick | Memoria USB | USB-poŝmemoro | Clé USB | Pen drive | USB ֆլեշ քարտ | USB flash drive | Clave de memoria USB | Chiave USB | דיסקון | USB-sleutel | USBメモリ | Minnepinne | PenDrive | USB Flashdisk | USB Flash drive | USB-ključ | USB-muisti | USB-minne | แฟลชไดรฟ์ | 闪存盘

 

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

Home Page • arts • business • computers • games • health • hospitals • home • kids & teens • news • physicians • recreation• reference • regional • science • shopping • society • sports • world