Encyclopedia
USB flash drives are
NAND-type
flash memory data storage devices integrated with a
USB interface. They are typically small, lightweight, removable and rewritable. Memory capacity typically ranges from 8 megabytes up to 64 gigabytes , limited only by current flash memory densities. As capacity increases, so does price, to a point.
As of 2006, more recent examples in the 1 to 4 GB range are little more expensive than the 128 MB versions available in 2002.
There are versions which use
FireWire as well, but since the
IEEE1394 standard is not as ubiquitous as USB, these are less common.
USB flash drives have several advantages over other portable storage devices, particularly the
floppy disk. They are generally faster, hold more data, and are considered more reliable than floppy disks. These types of drives use the
USB mass storage standard, supported natively by modern operating systems such as
Linux,
Mac OS X, and
Windows XP.
A flash drive consists of a small
printed circuit board encased in a robust plastic or metal casing, 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.
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.
History
The flash drive was first invented in 1998 by Dov Moran, President and CEO of M-Systems Flash Pioneers . 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 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 480 Mbit/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
Internals 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 | 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 . 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.
Size and style of packaging
Some manufacturers differentiate their products by using unnecessarily elaborate housings. An example is some of
Lexar's
Jump Drives which are often bulky and difficult to connect to the USB port.
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 extension cable to relieve tension on the port.
Common uses
Personal data transport- The most common use of flash drives is by individuals to transport and store personal files such as documents, pictures and video.
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 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.
Application carriers- 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. 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.
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 best-known of these has been Apple Computer's iPod shuffle, and the Creative Labs MuVo.
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.
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.
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. Top of the line 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 hundred thousand 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 or commonplace applications 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.
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.
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 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 750 MB-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 US$10 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.
Security
Some flash drives feature encryption of the data stored on them, generally using full disk encryption below the filesystem. 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 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
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.
Naming
No commonly recognized term for USB flash drives has emerged. The resulting confusion makes them more difficult for manufacturers to market and for consumers to research.
Future developments
Semiconductor 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 uses USB 2.0 and claims 10 years worth of information preservation.
Lexar is attempting to introduce a USB flash card , 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 and 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 machine wash. Leaving the flash drive out to dry completely has been known to result in a working drive with no future problems.
- Isolinear optical chips, fictional devices similar to USB drives in design and function, featured regularly in over 10 years before their real world counterparts were invented.
See also
References
External links
Security
- TrueCrypt - Free open-source full disk encryption software for Linux and Windows XP/2000/2003
- - Password management utility . Requires Windows.
- - Open source password management utility.
HOWTO pages
- - A guide on using Portable Firefox, Thunderbird, Instant Messenger in a secure way
- - Open source tools and a very clear walkthrough
- - Generic driver download for Windows 98 SE to allow USB flash drives to work
- Simple, easy screenshot walkthroughs showing how to put Linux distributions onto USB sticks
- Simple steps to run a Linux desktop on a flash drive
- Run Windows CE Emulator on a flash drive
- Run secure calendar/day planner entirely on a flash drive
