USB flash drive
Encyclopedia : U : US : USB : USB flash drive
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[link]), 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 [link], 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 [link] or metal casing [link], making the drive sturdy enough to be carried about in a pocket, as a keyfob, or on a lanyard. Only the USB connector protrudes from this protection, and is usually covered by a removable cap. Most flash drives use a standard type-A USB connection allowing them to be connected directly to a port on a personal computer. Some small drives have been made with a thin plug designed to mate with a standard USB port [link], 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.
- 1 History
- 2 Components
- 3 Strengths and weaknesses
- 4 Common uses
- 4.1 Computer repair
- 4.2 System administration
- 4.3 Flash drive for applications
- 4.4 Flash drives as audio players
- 4.5 Flash drives to boot operating systems
- 4.6 Flash drives in arcades
- 5 Security
- 6 Etymology
- 7 Comparison to other portable memory forms
- 8 Future developments
- 9 Trivia
- 10 See also
- 11 External links
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" [link] 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. [link]).
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. [link]
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. [link]
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. [link]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: