USB flash drive 400414 225921943 2008-07-16T00:58:43Z Bobo192 97951 Reverted edits by [[Special:Contributions/216.235.111.11|216.235.111.11]] ([[User talk:216.235.111.11|talk]]) to last version by Floodo1 {{Redirect|JumpDrive|the fictional propulsion system|Jump drive}} [[Image:USB flash drive.jpg|thumb|right|A USB flash drive, under 4 inches (10 cm) tall.]] A '''USB flash drive'''<!-- please do not add alternative names, see talk archives for long history --> is a [[Flash memory#NAND memories|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 to 4 inches or 2.5 to 10 cm), and weigh less than 2 ounces (60 g). Storage capacities typically range from <!-- please include refs if you change these numbers, shipping is best -->64 MB to 32 GB<ref>http://www.reghardware.co.uk/2007/07/30/toshiba_transmemory/</ref> or more. Some allow 1 million write or erase cycles<ref name="IPro"> "Imation Swivel Pro Flash Drive", About.com, 2008, webpage: [http://mobileoffice.about.com/od/portablefilestorage/gr/swivelproflash.htm AboutCom-Swivel-Pro-Flash]. </ref><ref name=wcycles/> and have 10-year data retention,<ref name="MOff"> "USB flash drive weighs 32 g", Trade Media Ltd, June 2006, webpage: [http://www.globalsources.com/gsol/I/USB-flash-drive/a/9000000076102.htm GSources-flash-6102].</ref> connected by [[USB 1.1]] or [[USB 2.0]]. USB [[Memory card]] [[card reader|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 much more data, have a more durable design, and are more reliable for lack of moving parts. 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 device class|USB mass storage]] standard, supported natively by modern operating systems such as [[Microsoft Windows|Windows]], [[Mac OS X]], [[Linux]], and other [[Unix-like]] systems. USB drives with USB 2.0 support can also be faster than an [[optical disc drive]], while storing a larger amount of data in a much smaller space. 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.<ref name="wcycles"> USB flash drives allow reading, writing, and erasing of data, with some allowing 1 million write/erase cycles in each cell of memory: if 100 uses per day, 1 million cycles could span 10,000 days or over 27 years. Some devices level the usage by auto-shifting activity to underused sections of memory. </ref> 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 [[Universal Serial Bus|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 through 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 properly unless plugged directly into a host controller (i.e., the ports found on the computer itself) or a self-powered hub. ==Technology== {{main|Flash memory|USB}} Flash memory is actually a combination of a number of older technologies, with the low cost, low power consumption and small size being made possible by recent advances in [[microprocessor]] technology. The memory storage is based on earlier [[EPROM]] and [[EEPROM]] technologies. These had very limited capacity, were very slow for both reading and writing, required complex high-voltage drive circuitry, and could only be re-written after erasing the entire contents of the chip. Later EEPROMS were developed where the erasure region was broken up into smaller "fields" that could be erased individually without affecting the others. Altering the contents of a particular memory location involved first copying the entire field into an off-chip buffer memory, erasing the field, and then re-writing the data back into the same field, making the necessary alteration to the relevant memory location while doing so. This required considerable computer support, and PC-Based EEPROM flash memory systems often carried their own dedicated microprocessor system. Flash drives are more or less a miniaturized version of this. The development of high-speed serial data interfaces such as [[USB]] for the first time made serially accessed storage memory systems viable, and the simultaneous development of small, high-speed, low-power microprocessor systems allowed this to be incorporated into extremely compact systems. Serial access also greatly reduced the number of electrical connections required for the memory chips, which has allowed the successful manufacture of multi-[[gigabyte]] capacities. (Every external electrical connection is a potential source of manufacturing failure, and with traditional manufacturing, a point is rapidly reached where the successful [[Semiconductor device fabrication|yield]] approaches zero). Modern flash memory systems are accessed very much like hard disk drives, where the controller system has full control over where information is actually stored. The actual EEPROM writing and erasure processes are, however, still very similar to the earlier systems described above. Many low-cost [[MP3 Player]]s simply add extra software to a standard flash memory control microprocessor so it can also serve as a music playback decoder. Most of these players can also be used as a conventional flash drive. ==History== === First commercial product === [[Image:Geil David 1GB AB.jpg|thumb|right|Flash drive with retractable USB connector]] Trek Technology and [[IBM]] began selling the first USB flash drives commercially in 2000. [[Singapore]]an company Trek Technology sold a model dubbed the "ThumbDrive," and [[IBM]] marketed the first such drives in North America, with its product the "DiskOnKey" (which was [[original equipment manufacturer|manufactured]] by [[M-Systems]]). IBM's USB flash drive became available December 15, 2000<ref>{{cite web |url=http://www-307.ibm.com/pc/support/site.wss/document.do?sitestyle=lenovo&lndocid=MIGR-4R3GWN |title=8MB USB Memory Key - Overview |publisher=www.ibm.com}}</ref><ref>{{cite web |url=ftp://ftp.software.ibm.com/pc/pccbbs/options/22p5250.pdf |title=8 MB USB Memory Key - User Guide - First Published December 2000 |publisher=www.ibm.com}}</ref>, and had a storage capacity of 8 [[mebibyte|MiB]], more than five times the capacity of the (at the time) commonly used [[floppy disk]]s. Lexar can also lay claim to a pioneering USB flash drive product. In 2000, it introduced a [[Compact Flash]] (CF) card with a USB connection. Lexar also offered a companion card reader and USB cable that eliminated the need for a USB hub. In 2004, Trek Technology brought several lawsuits against other USB flash drive manufacturers and distributors in an attempt to assert its patent rights to the USB flash drive. A court in Singapore ordered competitors to cease selling similar products<ref name="inventor">{{cite news| url=http://www.bangkokpost.com/breaking_news/breakingnews.php?id=70859| title=Singapore firm wins patent on thumb drive |publisher=The Straits Times | accessdate=2006-08-01}}</ref> that would be covered by Trek's patent, but a court in the United Kingdom revoked <ref>{{cite web|url=http://www.ipo.gov.uk/patent/p-decisionmaking/p-challenge/p-challenge-decision-results/p-challenge-decision-results-bl?BL_Number=O/318/06|title=Patent decision}}</ref> one of Trek's patents in that country. === Second generation === [[Image:ToshibaUSB.jpg|thumb|right|Toshiba TransMemory Flash Drive with cover on. Comes pre-installed with [[U3]], allowing users to take their applications, fully installed and operational, to any desktop.]] Modern flash drives have [[USB 2.0]] connectivity. However, they do not currently use the full 480&nbsp;[[megabit|Mbit]]/s the specification supports due to technical limitations inherent in NAND flash. The fastest drives currently available use a dual channel controller, although they still fall considerably short of the transfer rate possible from a current generation hard disk, or the maximum high speed USB throughput. Typical overall file transfer speeds are about 3 [[megabyte|MB]]/s. The highest current overall file transfer speeds are about 10-60 MB/s. Older, "full speed" 12 Mbit/s devices are limited to a maximum of about 1 MB/s.{{Fact|date=May 2008}} ==Design and implementation== One end of the device is fitted with a single [[Gender of connectors and fasteners|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-mount technology|surface-mounted]] [[integrated circuit]]s (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]]. {| border="1" cellpadding="4" align="right" cellspacing="0" style="background: #f9f9f9; border: 1px #aaa solid; border-collapse: collapse; margin-left: 1em;" | style="background: #E7E7E7;" align="center" colspan=2 | [[Image:Usbkey internals.jpg|350px|]]<br>'''Internals of a typical USB flash drive''' |- !1 |USB connector |- !2 |USB mass storage controller device |- !3 |Test points |- !4 |[[Flash memory|Flash memory chip]] |- !5 |[[Crystal oscillator]] |- !6 |[[LED]] |- !7 |[[Write protection|Write-protect]] switch |- !8 |Space for second flash memory chip |} ===Essential components=== There are typically four 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. The controller contains a small [[RISC]] microprocessor and a small amount of on-chip [[Read-only memory|ROM]] and [[Random Access Memory|RAM]]. *NAND flash memory chip — stores data. NAND flash is typically also used in [[digital camera]]s. *[[Crystal oscillator]] — produces the device's main 12&nbsp;MHz [[clock signal]] and controls the device's data output through a [[phase-locked loop]]. ===Additional components=== The typical device may also include: *[[Jumper (computing)|Jumpers]] and test pins — for testing during the flash drive's manufacturing or loading code into the microprocessor. *[[light-emitting diode|LEDs]] — indicate data transfers or data reads and writes. *[[write protection|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 or the main body contains a hole suitable for connection to a [[key chain]] or [[lanyard]]. ===Size and style of packaging=== [[Image:sushiusb.jpg|thumb|Flash drives come in various, sometimes bulky or novelty, shapes and sizes, in this case [[Roe|ikura]] sushi]] Some manufacturers differentiate their products by using elaborate housings, which are often bulky and make the drive difficult to connect to the USB port. Because the [[USB#USB connectors|USB port connectors]] on a computer housing are often closely spaced, plugging a flash drive into a USB port may block an adjacent port. Such devices may only carry the USB logo if sold with a separate extension cable. USB flash drives have been integrated into other tools commonly carried on one's person such as watches, pens, and even the [[Swiss Army knives|Swiss Army Knife]]; others have been fitted with novelty cases such as toy cars or [[LEGO]] bricks. The small size, robust nature and relatively low price of USB flash drives makes them an increasingly popular peripheral for [[case modding]]. Overweight or ill-fitting flash drive packaging can cause disconnection from the host computer. This can be overcome by using a short USB to USB (male to female) extension cable to relieve tension on the port. Such cables are USB-compatible, but do not conform to the USB 1.0 standard. <ref name=usb1>{{PDFlink|[http://www.usb.org/developers/whitepapers/cablew~1.pdf USB 1.0 Spec Position on Extension Cables and Pass-Through Monitors]|13.7&nbsp;[[Kibibyte|KiB]]<!-- application/pdf, 14126 bytes -->}}</ref> <ref name=usb2>{{PDFlink|[http://www.usb.org/developers/docs/ecn1.pdf USB 2.0 Specification Engineering Change Notice (ECN) #1: Mini-B connector]|958&nbsp;[[Kibibyte|KiB]]<!-- application/pdf, 981022 bytes -->}}</ref> ===File system=== {{main|List of file systems#Flash memory / solid state media file systems}} Most flash drives ship preformatted with the [[File Allocation Table|FAT]] or [[File_Allocation_Table#FAT32|FAT 32]] [[file system]]. The ubiquity of this file system allows the drive to be accessed on virtually any host device with USB support. Also, standard FAT [[Disk checker|maintenance utilities]] (e.g. [[ScanDisk]]) can be used to repair or retrieve [[Data corruption|corrupted data]]. However, because a flash drive appears as a USB-connected [[hard drive]] to the host system, the drive can be [[Disk formatting|reformatted]] to any file system supported by the host operating system. It is worth noting that while [[defragmentation]] utilities can be run against a flash drive, there is no point in doing so. Defragmentation is a process intended to optimize access to data on a drive with spinning [[Hard disk platter|platters]] and moving [[Disk read-and-write head|heads]]; however, since flash memory is truly random-access (a read to an adjacent cell is no faster than a read from any other cell), there is no performance gain. Further, the flash controller [[Abstraction (computer science)|abstracts]] the physical memory location used for a given "sector", so that the host machine doesn't really know the layout of the data. Finally, as the defragmentation process moves data around, attempting to optimize it, a small portion of the flash memory's [[Flash_memory#Memory_wear|wear life]] is consumed. <!-- Note: Please don't add JFFS or YAFFS references to this article. While these two file systems, designed to minimize the inherent weaknesses of flash memory (e.g. memory wear), can be used on a UFD, they provide no significant benefit. These filesystems are intended to assist with directly-addressed flash memory (e.g. SmartMedia through a raw reader). A UFD's memory layout is abstracted from the host system in the USB mass storage class, and the UFD's controller chip performs tasks similar to those JFFS and YAFFS are intended for. --> == Uses== ===Personal data transport=== The most common use of flash drives is to transport and store personal files such as documents, pictures and videos. Individuals also store medical alert information on MedicTag flash drives for use in emergencies and for disaster preparation. ===Secure storage of data, application and software files=== With wide deployment(s) of flash drives being used in various environments (secured or otherwise), the issue of data and information security remains of the utmost importance. The use of [[biometrics]] and [[encryption]] is becoming the norm with the need for increased security for data; [[OTFE]] systems such as [[FreeOTFE]] and [[TrueCrypt]] are particularly useful in this regard, as they can transparently encrypt large amounts of data. ===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. ===Computer repair=== Flash drives enjoy notable success in the PC repair field as a means to transfer recovery and antivirus software to infected PCs, while allowing a portion of the host machine's data to be archived in case of emergency. As the drives have increased in storage space, they have also replaced the need to carry a number of CD ROMs and installers which were needed when reinstalling or updating a system. ===Application carriers=== Flash drives are used to carry [[List of portable software|applications]] that run on the host computer [[Portable software|without requiring installation]]. While any standalone application can be used this way, the [[U3]] company, works with drive makers (parent company [[SanDisk]] as well as others) to deliver Windows applications from a flash drive custom-tuned for this purpose. U3 also provides a software framework for [[ISV]]s interested in their platform. [[Ceedo]] is an alternative product with the key difference that it does not require Windows applications to be modified in order for them to be carried and run on the drive. ===Computer Forensics - Law enforcement=== A recent development for the use of a USB Flash Drive as an application carrier is to carry the [[Computer Online Forensic Evidence Extractor]] (COFEE) application, developed by [[Microsoft]]. COFEE is a set of applications designed to search for and extract [[Computer forensics|digital evidence]] on computers confiscated from suspects<ref>{{cite web|url=http://seattletimes.nwsource.com/html/microsoft/2004379751_msftlaw29.html |title=Microsoft device helps police pluck evidence from cyberscene of crime|publisher=The Seattle Times|accessdate=2008-04-29}}</ref>. ===To boot operating systems=== Most current PC firmware permits booting from a USB drive, allowing the launch of an operating system from a [[bootable]] flash drive. Such a configuration is known as a [[Live USB]]. While a Live USB could be used for general-purpose applications, size and memory wear make them poor choices compared to alternatives. They are more suited to special-purpose or temporary tasks, such as: * Loading a minimal, hardened kernel for embedded applications (e.g. network router, firewall). * Bootstrapping an operating system install or [[disk cloning]] operation, often across a network. * Maintenance tasks, such as virus scanning or low-level data repair, without the primary host operating system loaded. ===Windows Vista ReadyBoost=== In [[Windows Vista]], the [[ReadyBoost]] feature allows use of some flash drives to augment operating system memory. ===Audio players=== Many companies make [[solid-state drive|solid-state]] [[digital audio player]]s in a small [[form factor]], essentially producing flash drives with sound output and a simple user interface. Examples include the [[Creative MuVo]] and the [[iPod shuffle]]. While a few of these players fit the accepted definition of a "true" USB flash drive (including the ability to plug directly into a USB A socket), the majority require a separate cable. Many of the smallest players also contain a rechargeable battery, charged from the USB interface. ===Music storage=== [[Digital audio]] [[Audio file formats|files]] can be transported from one computer to another like any other document, and played on a compatible [[Media player (application software)|media player]] (with caveats for [[Digital rights management|DRM]]-locked files). In addition, many home [[Hi-Fi]] and [[car audio|car stereo head units]] are now equipped with a USB port. This allows a USB flash drive, loaded with media files (usually [[MP3]] or [[Windows Media Audio|WMA]], although sometimes other formats such as [[Ogg]]/[[Vorbis]] may be used), to be played directly. Most often, these files will be from the user's personal collection (e.g. [[Ripping|ripped from CD]] or [[Online music store|purchased online]]), although there have been some examples of pre-encoded music sold or given away for promotion on USB flash drives: * In 2004, the German band [[WIZO]] made a recording industry first of releasing the "Stick EP", an album available only as a USB drive. In addition to five high-[[bitrate]] MP3s, it also included a video, pictures, lyrics, and [[Tablature|guitar tablature]]. * ''[[Third (Portishead album)|Third]]'' album by Portishead in the limited edition box set. * ''[[Not Here to Please You]]'' EP by [[Hadouken!]] * ''[[Icky Thump (song)|Icky Thump]]'' single by [[White Stripes]] * ''[[Good Life (Kanye West song)|Good Life]]'' single by [[Kanye West]]<ref>[http://www.fmqb.com/Article.asp?id=16691 CHR &ndash; Available for Airplay]. FMQB. Accessed [[September 23]] [[2007]].</ref> * ''[[X (Kylie Minogue album)|X]]'' album by [[Kylie Minogue]] * [[Nine Inch Nails]] promoted their album ''[[Year Zero (album)|Year Zero]]'' by hiding USB drives at concerts, usually with content like select songs contained on them. * ''[[Nothing in My Way|Nothing In My Way]]'' single by [[Keane (band)|Keane]]<ref>[http://crave.cnet.com/8301-1_105-7887-1.html?tag=blog.5 Keane's flash-y new single]. Crave. Accessed [[April 4]] [[2008]].</ref> The 512[[MiB]] drive was loaded with the audio track, [[music video]], and several [[Nothing_in_My_Way#512_MB_USB_memory_stick_content|extras]]. * ''[[The Bedlam in Goliath]]'' album by [[The Mars Volta]] was released on a USB drive shaped like a [[ouija]] [[planchette]] to coincide with the album's concept. In addition to the music files, the drive can be used to unlock exclusive material on the band's website. * In 2007, a product known as the MU-STIK appeared in the market, offering a means of packaging music albums by containing all relevant digital audio/video data and a customizable player interface within a USB key.<ref name="365magarticle">{{cite web|url=http://www.365mag.com/index.php?pg=news&recnum=3899&Title=CC+SoundFactory+presents+Shiok+Waves+album+on+a+memory+stick+on+365MAG+International+Music+Magazine | title=CC Sound Factory Presents Shiok Wave Album on a Memory Stick | accessdate=2007-07-23}}</ref> * ''[[The I Heart Revolution: With Hearts as One]]'' album by [[Hillsong United (band)|Hillsong United]] was released in [[2008]] on a flash drive embedded in a black rubber wristband. In addition to the music files, the drive included the lyrical [[overhead projector|overhead]] master sheets, a [[Portable Document Format|PDF]] copy of the liner sleeve, and the two versions of the album cover.<ref>{{cite web| url=http://www.hillsong.com/music/product.php?xProd=4559 | title=PART ONE/// WITH HEARTS AS ONE USB Wristband | publisher=Hillsong.com | accessdate=2008-04-12}}</ref> ===In arcades=== In the [[arcade game]] ''[[In the Groove (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. As of software revision 21 (R21), players can also store custom songs and play them on any machine on which this feature is enabled. While use of flash drives is common, the drive must be [[Linux]] compatible, causing problems for some players. ===Brand/product promotion=== The availability of inexpensive flash drives has enabled them to be used for [[Promotion (marketing)|promotional]] and [[marketing]] purposes, particularly within technical and computer-industry circles (e.g. technology [[Trade fair|trade shows]]). These may be given away for free, sold at less than wholesale price, or included as a bonus with another purchased product. Usually, such drives will be custom-stamped with a company's [[logo]], as a form of [[advertising]] to increase [[mind share]] and [[Brand|brand awareness]]. Sometimes, the drive is simply an ordinary blank drive for the customer's use, and simple advertising is the only purpose. Often, however, the drive's storage may be preloaded with graphics, documentation, web links, [[Adobe Flash|Flash]] [[animation]] or other [[multimedia]], and even free or demonstration software. In some cases, such preloaded drives may have had an internal [[Signal trace|wiring trace]] severed to disable writing (rendering the drive as [[Read-only memory|read-only]] to the end-user). This serves the dual-purposes of ensuring that the original promotional data remains intact (and isn't simply deleted to free up capacity), as well as reducing the possibility that drives will become infected with a [[Computer virus|virus]] or other [[malware]] before reaching the customer. An alternative is that some drives can be configured with two separate partitions: one read-only (preloaded with the promotional data), and another writable and blank for the end-user's use. However, such dual-purpose drives tend to be more expensive, thus reducing their suitability as promotional items. USB Flash Drives can also be set up with an autorun feature to display or start up preloaded presentations, websites and articles immediately on insertion of the drive. This can be accomplished by saving a file called autorun.inf in the root directory of the drive. This file needs to contain appropriate shell script telling the operating system which files to execute.<ref name=cp1>[http://www.flashbay.com/usb_flash_drive_autorun_setup.html USB flash drive auto run setup], article from Flashbay.com </ref> The auto run feature is often used on promotional flash drives to increase the probability that the recipient reads the preloaded promotional material or visits a particular website. ===Backup=== Some [[value-added reseller]]s are now using a flash drive as part of small-business [[turnkey]] solutions (e.g. [[Point of sale|point-of-sale]] systems). The drive is used as a [[backup]] medium: at the close of business each night, the drive is inserted, and a [[database]] backup is saved to the drive. Alternatively, the drive can be left inserted through the business day, and data is regularly updated. In either case, the drive is removed at night and taken offsite. This strategy has several advantages. First, it can be made relatively simple for the end-user. This increases the likelihood that backups will be performed regularly (one of the most common reasons for a failure to backup is the complexity of the process). Second, because the drive is small, it is easy to carry by the manager or proprietor, thus ensuring that the data is offsite for [[disaster recovery]]. Third, flash drives are very robust and reliable, particularly compared to other backup media (e.g. [[Magnetic tape data storage|tape]], [[Optical disc recording technologies|optical media]]). Fourth, the availability of large drives often permits the storage of several backup images on a single medium, facilitating a [[Grandfather-father-son backup|GFS]] or other hierarchical backup strategy (multiple flash drives are another option, but this increases the backup complexity). Finally, the flash solution is often far cheaper than alternatives, which may require additional hardware or recurring media costs (e.g. [[tape drive]], [[DVD recordable|blank DVDs]]). ==Advantages and disadvantages== === Advantages=== Flash drives are nearly [[wikt:impervious|impervious]] to the [[scratch]]es and dust that were problematic for previous forms of portable storage, such as [[compact disc]]s, [[Iomega Zip drive|ZIP disks]], and [[floppy disk]]s, 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. Many can hold more data than a [[Compact disc|CD]] (703<ref>TDK rewriteable disk</ref> [[Megabyte|MB]]). Top of the line flash drives can store more data than a [[DVD]] (4.7 [[Gigabyte|GB]]), and flash drives with 64 GB storage are now available. The power consumption of a typical flash drive is very low; the common alternative, the [[hard disk enclosure|portable hard disk]], might take 3 to 4 times the power for 10 to 100 times the capacity. Flash drives have no moving parts, hard disks, on the other hand, require several [[motors]] or [[actuators]] to rotate the [[disk platter]], and move the [[disk read-and-write head|read / write head]]. Consequently, the USB flash drive need not be as heavy, allowing greater portability. Flash drives implement the USB mass storage device class, meaning that most modern [[operating system]]s can read and write to flash drives without any additional [[device driver]]s. The flash drives present a simple block-structured logical unit to the host operating system, hiding the individual complex implementation details of the various underlying flash memory devices. The operating system can use whatever type of [[file system]] or block addressing scheme it wants. Some computers have the ability to [[Booting#Boot devices|boot up]] from flash drives. Flash drives are much more tolerant of abuse than mechanical drives, but can still be damaged or have data corrupted by severe physical impacts. Improperly wired USB ports can also destroy the circuitry of a flash drive, a danger in home-built desktop PCs.{{Dubious|date=April 2008}} Some flash drives can retain their memory after being submerged in water <ref name="in water">{{cite web|url=http://www.kingmaxdigi.com/news/news_product/news_p20051114.htm | title= Kingmax Super Stick | accessdate=2006-08-01}}</ref>, even through a machine wash. Leaving the flash drive out to dry completely before allowing current to run through it has been known to result in a working drive with no future problems. [[Five (channel)|Channel Five]]'s [[Gadget Show]] cooked a flash drive with propane, froze it with [[dry ice]], submerged it in various acidic liquids, ran over it with a jeep and fired it against a wall with a mortar. A company specializing in recovering lost data from computer drives managed to recover all the data on the drive. <ref>[http://www.youtube.com/watch?v=NyOFIH-6WGs testing removal media] on the Gadget Show.</ref> All the other removal storage devices, using optical or magnetic discs or semiconductor ([[Secure Digital card|Secure Digital]]) were completely destroyed. ===Disadvantages=== Like all flash memory devices, flash drives can sustain only a limited number of write and erase cycles before failure<ref name=lwn>http://lwn.net/Articles/234441/</ref>. Mid-range flash drives under normal conditions will support several hundred thousand cycles<ref name=lwn />, 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]] in [[Live USB]]) <ref>http://linux-usb.sourceforge.net/USB-guide/x498.html</ref> 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 the computer's main RAM rather than store them temporarily on the flash drive. Most USB flash drives do not include a write-protect mechanism, although some have a switch on the housing of the drive itself to keep the host computer from writing or modifying data on the drive. Write-protection makes a device suitable for repairing [[computer virus|virus]]-contaminated host computers without risk of infecting the USB flash drive itself. A drawback to the small size is that they are easily misplaced, left behind, or otherwise lost. This is a particular problem if the data they contain are sensitive (see [[data security]]). As a consequence, some manufacturers have added encryption hardware to their drives -- although [[Comparison of disk encryption software|software encryption systems]] achieve the same thing, and are universally available for all USB flash drives. Others just have the possibility of being attached to keychains, necklaces and lanyards. Compared to other portable storage, particularly external hard drives, USB flash drives have a high price per unit storage and are only available in comparatively small capacities. ==Comparison with other portable memory forms== Flash storage devices are often compared to other common, portable, swappable data storage devices, such as [[floppy disks]], [[Zip disk]]s, [[miniCD]] / [[miniDVD]], [[CD-R]]/[[CD-RW]] and DVD-RW discs. ===Floppy disk=== Following magnetic tape, the floppy disk was the first popular method of file transport; but floppies have been almost completely phased out due to their low capacity, low speed, and low durability. Virtually no new computers include floppy drives, but they do include USB ports. However, floppy disks are still being used because of their low cost, are often the easiest or only way to share files with older systems, are easily bootable, and because floppy drives can be added to new systems in external or internal forms. In addition, office workplaces have often disabled high volume writable media such as optical drivers and USB ports to prevent employees from taking large amounts of data, so the small capacity of the floppy limits the information compromised. ===Zip drive=== Attempts to extend the floppy standard (such as the [[Imation]] [[SuperDisk]]) were not successful because of a reputation for unreliability 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 750&nbsp;MB—cannot be read on older drives. Unless one were to carry 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 costing US$10 or more. Because moving parts are involved and the material used for creating the storage medium in Zip disks is similar to that used in floppy disks, Zip disks have a [[Click of death|high risk of failure and data loss]] compared to flash drives. Larger removable storage media, like Iomega's [[Jaz drive]], had even higher costs for both drives and media, and as such were not pervasively adopted as a floppy alternative. ===Optical media=== CD-R and CD-RW are swappable storage media alternatives. Unlike Zip and floppy drives, DVD and [[CD recorder]]s are now common in personal computer systems. CD-Rs can be written to only once. But CD-RWs are rated at up to 1,000 erase/write cycles, and modern NAND-based flash drives often last for 500,000 or more erase/write cycles. Optical storage devices are generally among the cheapest methods of mass data storage after the hard drive. However, optical devices are slower than their flash-based counterparts. In addition, optical discs with a 12&nbsp;cm diameter can be inconveniently large and, unlike flash drives, cannot fit into a pocket or hang from a key chain. Smaller optical media do exist, such as business card CD-Rs which have the same dimensions as a credit card, and the slightly less convenient but higher capacity 8&nbsp;cm recordable CD/DVDs. But these are harder to obtain and generally more expensive than the standard 12&nbsp;cm version. The small discs also require a tray-loading drive (or a ring adapter, but these are rare); they can cause damage if inserted directly into a slot-loading drive. Universal Disk Format versions 1.50 and above have facilities to support rewritable discs like sparing tables and virtual allocation tables, but many older operating systems do not understand these versions or facilities. Packet-writing utilities like [[DirectCD]] and [[InCD]] exist but produce discs that are not universally readable (despite claims to be based on the [[Universal Disk Format|UDF]] standard). The [[Mount Rainier (packet writing)|Mount Rainier]] standard addresses this shortcoming in CD-RW media by running the older file systems on top of it and performing defect management for those standards, but it requires support from both the CD/DVD burner and from the operating system. Many drives made today do not support Mount Rainier, and many older operating systems like Windows XP and below, and the Linux kernel versions below 2.6.2 do not support it. Windows Vista and Linux kernels 2.6.2 and newer support Mount Rainier. As a result, CDs/DVDs are a good way to record a great deal of information cheaply and have the advantage of being readable by most standalone players, but they are poor at making ongoing small changes to a large collection of information; flash drives' ability to do this is their major advantage. ===External hard disk=== {{main | External hard disk}} Particularly with the advent of USB, external hard disks have become common and relatively inexpensive. External hard disk drives cost less than flash memories of the comparable capacity, and are available in the much larger capacities. For the host-to-drive connection, hard disks frequently offer multiple interfaces and/or faster interfaces than USB (e.g. [[IEEE 1394]]). For consecutive sector reads (for example, from an unfragmented file), most hard drives can provide a much higher sustained data rate than current NAND flash memory. However, hard drives are far more fragile than flash drives: they are less resistant to shock, have limitations on use at high altitude, and (like all magnetic media) are vulnerable when exposed to electromagnetic fields. Hard drives are usually larger and heavier than flash drives, although not necessarily when compared per unit storage. Hard disks also suffer from file fragmentation (some filesystems are resistant to fragmentation, but no filesystem is completely immune), which can significantly reduce performance. ==Security== Some flash drives feature encryption of the data stored on them, generally using [[full disk encryption]] below the file system. 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 compatible encryption software, for which no portable standard is widely deployed. Some [[List of portable software#Real-Time Disk.2FVolume Encryption|encryption applications]] 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 the correct operating system. Other flash drives allow the user to configure secure and public partitions of different sizes. Executable files for Windows, Macintosh, and Linux may be on the drive, depending on manufacturer support. Some security software may require administrative rights on the host PC to access data. Newer flash drives support [[biometric]] [[fingerprinting]] to confirm the user's identity. As of mid-[[As of 2005|2005]], this was a relatively costly alternative to standard password protection offered on many new USB flash storage devices. Most fingerprint scanning drives rely upon the host operating system to validate the fingerprint via a software driver, often restricting the drive to [[Microsoft Windows]] computers. However, there are USB drives with fingerprint scanners use controllers that allow access to protected data without any authentication.<ref>[http://www.heise-online.co.uk/security/Secure-USB-sticks-cracked--/features/110280 Access to protected data areas without the right fingerprint]</ref> Some manufacturers deploy [[Dongle|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. All such forms of data protection security involve an increased risk of loss of access to the data by the legitimate owner/user. 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 [[rootkit]]s or [[packet sniffer]]s. 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]]. ==Naming== Recently, "USB flash drive" or simply "UFD" has emerged as the de facto standard term for these devices, although potentially confusing alternatives (such as [[Memory Stick|memory stick]]) are still prevalent. The myriad different brand names and terminology used, in the past and currently, make UFDs more difficult for [[manufacturer]]s to [[marketing|market]] and for [[consumers]] to research. Some commonly used names are actually trademarks of particular companies, such as Cruzer, TravelDrive, ThumbDrive, and Disgo. <!-- please do not add alternative names, see talk archives for long history --> ==Future developments== Semiconductor corporations have worked to 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. Flash drive capacities on the market are continuously increasing. As of 2008, 256&nbsp;MB and smaller capacity flash memory has been largely discontinued, and 512&nbsp;MB capacity flash memory is being phased out. High-speed is now a standard for modern flash drives and capacities of up to 64&nbsp;GB are available <ref>[http://www.engadget.com/2006/03/29/buslinks-64gb-usb-2-0-flash-drive-pro-2-series/ BUSlink's 64GB USB 2.0 Flash Drive PRO 2 Series]</ref>. [[Lexar]] is attempting to introduce a [[USB FlashCard]] <ref name=lexarpress>[http://www.lexar.com/newsroom/press/press_12_13_04.html Lexar Unveils New USB Card Form Factor and Introduces New USB FlashCard]</ref> <ref name=lexarufc>[http://www.lexar.com/ufc/ USB FlashCard (UFC) Highlights]</ref>, which would be a compact USB flash drive intended to replace various kinds of flash memory cards. [[Pretec]] introduced a similar card, which also plugs into every USB port, but is just one quarter the thickness of the Lexar model <ref name=pretec>[http://www.pretec.com/epages/Store.storefront/?ObjectPath=/Shops/Store.Pretec/Products/Q2UXXX Pretec i-Disk Diamond (the smallest USB flash drive)] </ref> SanDisk has a product called SD Plus, which is a [[SecureDigital]] card with a USB connector.<ref>{{cite web|url=http://www.dpreview.com/news/0501/05010606sandisksdflip.asp|title=SanDisk Ultra® II SD™ Plus Cards|publisher=SanDisk|accessdate=2008-03-02}}</ref> SanDisk has also 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]]. ==See also== {{portalpar|Electronics|Nuvola_apps_ksim.png}} *[[Disk enclosure|External hard drive]] *[[File synchronization]] *[[Flash drive]] *[[Live USB]] *[[PHILM]] *[[Pocket hard drive]] *[[Portable application]] *[[Sneakernet]] *[[USB Flash Drive Alliance]] *[[USB Mass Storage Device]] *[[Universal Flash Storage]] ==Notes== {{reflist|2}} ==References== * "Imation Swivel Pro Flash Drive", About.com, 2008, webpage: [http://mobileoffice.about.com/od/portablefilestorage/gr/swivelproflash.htm AboutCom-Swivel-Pro-Flash]. ==External links== {{commons}} * [http://www.bangkokpost.com/breaking_news/breakingnews.php?id=70859 Singapore firm wins patent on thumb drive] {{Audio format}} [[Category:Computer storage devices]] [[Category:Solid-state computer storage media]] [[Category:USB|Flash drive]] [[bn:ইউএসবি ফ্লাশ ড্রাইভ]] [[bs:USB stick]] [[br:Alc'hwez USB]] [[ca:Memòria USB]] [[cs:USB flash disk]] [[da:USB-nøgle]] [[de:USB-Massenspeicher]] [[et:Mälupulk]] [[es:Memoria USB]] [[eo:USB-poŝmemorilo]] [[fr:Clé USB]] [[gl:Memoria USB]] [[ko:USB 플래시 드라이브]] [[hy:USB ֆլեշ կրիչ]] [[hsb:USB-tykač]] [[id:USB flash drive]] [[ia:Clave de memoria USB]] [[it:Chiave USB]] [[he:דיסקון]] [[lb:USB-Späicherstëft]] [[hu:Pendrive]] [[ml:യു.എസ്.ബി. ഫ്ലാഷ് ഡ്രൈവ്‌]] [[ms:Pemacu kilat USB]] [[nl:USB-stick]] [[ja:USBメモリ]] [[no:Minnepinne]] [[nn:Minnepinne]] [[pl:Pamięć USB]] [[pt:USB Flashdisk]] [[ru:USB flash drive]] [[simple:USB flash drive]] [[sk:Jednotka USB flash]] [[sl:USB-ključ]] [[fi:USB-muisti]] [[sv:USB-minne]] [[th:แฟลชไดรฟ์]] [[vi:Ổ USB]] [[tr:USB Bellek Aygıtı]] [[vec:Ciaveta USB]] [[zh:闪存盘]]