USB flash drive
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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. This hot-swappable, non-volatile, solid-state device is usually compatible with systems that support the USB version the drive uses. Depending on the drive type and which OS version, and in some cases what patches are installed, the drives generally work with Windows 98, Macintosh platforms that support USB, and most Unix-like platforms that support USB, and Windows NT/2000/XP.
USB Flash Drive are also known as "pen drives", "thumb drives", "flash drives", "USB keys", "USB memory keys", "USB sticks", "jump drives", "keydrives","vault drives" and many more names. They are also sometimes called memory sticks, which is also a Sony trademark describing their brand of memory card.
A flash drive consists of a small printed circuit board encased with a robust plastic casing, making the drive sturdy enough to be carried around in a pocket, as a keyfob, or on a lanyard. Only the USB connector protrudes from this plastic protection, and is often covered by a removable plastic cap. Most flash drives feature the larger type-A USB connection, although some feature the smaller "miniUSB" connection.
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 V). 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.
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.
| Contents |
Components
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Missing image | |
| 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 |
This photograph shows both sides of the printed circuit board inside a typical flash drive (circa 2004). The flash drive in this photograph is a 64 Mbyte USB2.0 device with its plastic case removed.
One end of the device is fitted a single male type-A USB connector. Inside the plastic casing is a small, highly cost-engineered, printed circuit board. Mounted on this board are some simple power circuity 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 provides the flash memory storage.
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 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 feature retractable USB connectors.
- 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 both.
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 insults (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 (post-1996) computers means that such a drive will work in most places and that problems with device and driver incompatibilities are unlikely.
Flash drives are also a relatively dense form of storage - even the cheapest will store more than dozens of floppy disks, and a moderately priced one will carry as much as a CD. Historically, flash drive capacity has ranged from a few megabytes in size up to a few gigabytes, although some computers have trouble reading and writing to devices that have more than 2 GB of storage. 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 USB keys featuring USB 2.0 interfaces. Although USB 2.0 tops out at 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. This way 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 the 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).
Common uses
Network administration
Flash drive are particularly popular among system and network administrators, who load them with configuration information and with software used for system maintenance, troubleshooting, and recovery. The write protect feature on the flash drive is particularly useful for such uses, as it allows the system administrator to plug a flash drive containing anti-virus, spyware-removal, or trouble diagnosis software onto a suspect machine without risking the transmission of a virus or worm.
Flash drive for applications
Flash drive are also used to carry applications, which 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 (http://networkimprov.net/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 rudimentary user interface. Others produce small solid-state mp3 players which contain a removable flash drive. The most successful of these has likely been the iPod shuffle.
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 move the (large, and frequently impossible-to-remember) cryptographic key around by some other means.
There are applications (TrueCrypt, Private Disk (http://www.private-disk.net/), etc.) which allow running without installation. The executable files can be stored on the USB drive, together with the encrypted file-image. This means that the encrypted partition can be accessed on any computer running Microsoft Windows. The newer Lexar JumpDrive Secure (http://www.lexar.com/jumpdrive/jd_secure.html) allows the user to configure secure and public partitions of different sizes. The executable files are included on the drive for Windows, Macintosh, and Linux.
Newer flash drives now support biometric fingerprinting to confirm the identity of the user. 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, whether by containing encryption keys or (more commonly) by 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 drive also pose large organisations a significant security problem. 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 organisations (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.
Naming confusion
The abundance of different names for these devices has often been a source of confusion. With no common name agreed upon, it has been more difficult for manufacturers to market the product, and for consumers to find information, compare prices (particularly on price-comparison websites), or discuss it with others. Some feel that this may have slowed the widespread adoption of this technology.
Among the names are:
- Keyfob - Widely used in the Seattle area
- flash drives
- jump drives - Lexar sells their drives under this trademarked name
- keychain drives
- keydrives
- Kikinou (primarily in French)
- micro hard drives
- pen drives
- Piripicho (primarily in Spanish)
- pocket drives
- thumb drives
- USB flash drives
- USB flash memory drives
- USB keys
- USB memory keys
- USB memory stick - The term is also often used informally despite the fact memory stick is a Sony trademark.
- USB sticks
- vault drives -Sony's USB storage devices started using this name as of March 2005
Comparison to other forms of portable memory
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 each still available on the market as storage media, despite their declining popularity. While 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 have essentially become obsolete due to their low capacity (1.44 MB) and their relatively low speed. Floppies were the first publicly-popular method of file transportation, but an increasing number of systems are now sold without a floppy drive, the Apple iMac being the first. Very few systems may be purchased without a USB interface. Overall, the faster flash memory, with its nearly universally available USB interface, is more convenient than floppies. Floppy disks are still in use because of their ease of use with older systems (Windows 98 is still fairly common and does not support USB flash sticks without extra drivers), and the low cost of disks.
Zip, while popular at some times in some niches, 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 costs per megabyte were fairly high (though flash, at least until recently, also had fairly high per-megabyte costs) 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. Iomega's Jaz drive, as well, never caught on enough to replace the floppy disk.
CD-R and CD-RW are swappable storage media alternatives. Unlike Zip and floppy drives, DVD and CD recorders are becoming increasingly common in personal computer systems. While CD-Rs are not susceptible to read/write wear (they can, after all, only be written to once), CD-RWs are rated at 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 can also be inconveniently large and, unlike flash drives, cannot into fit in a pocket or hang from a keychain. There is also no standard file system for rewriteable optical media; packet-writing utilities like DirectCD and InCD exist, but produce discs which are not universally readable despite claiming to be based on the UDF standard. The upcoming Mount Rainer 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, large, durable, and compact. Unlike Zip and floppies, flash memory lacks moving parts, making them 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 keydrive, doing so by integrating various keydrive functions in a single chip, and thus reducing the part-count and overall package cost. As of 2004 some manufacturers are planning to include more ICs so that the storage and logic/communications functions are packaged in a single, ultra-low-cost device.
Trivia
In 2004, the German punk band WIZO was the first artist to release music in MP3 format on a USB drive entitled the "WIZO Stick-EP."
See also
External links
Keydrive applications
- Listing of USB keydrive applications (http://www.usbapps.com)
- airWRX: USB Keydrive application framework (http://networkimprov.net/airwrx/)
- Freeware programs to run from a USB stick (http://www.kikizas.net/en/usbapps.html)
- RUNT: ResNet Network Tester for USB Keydrives (http://www.ncsu.edu/project/runt/)
GNU/Linux distributions for USB
- DamnSmallLinux (DSL), a small derivative of Knoppix, tailored to USB (http://rz-obrian.rz.uni-karlsruhe.de/knoppix-usb/)
- featherlinux - GNU/Linux distribution specifically created for USB sticks (http://featherlinux.berlios.de/)
- flash-puppy a mature distro designed for keydrives (http://www.goosee.com/puppy/)
- Flonix: USB Keydrive Operating System (http://www.flonix.com/usbedition/article.php?id_article=13)
- Generic Howto on USB booting, incl. with using a floppy/CD for the initial boot if the BIOS does not support USB (http://www.freewebs.com/tsj/bootingUSB_ldp_v0.1.htm)
- Installing GNU/Debian Linux from a USB stick (http://d-i.pascal.at/)
- LiveDistro.org - Operating systems and HOWTOs for LiveUSBs (http://www.livedistro.org)de:USB-Stick
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