USB flash drives
are NAND-type flash memory data storage devices
integrated with a USB interface. They are typically small, lightweight,
removable and rewritable. As of November 2006, memory capacities for USB Flash
Drives commonly are found from 128 megabytes up to 64 gigabytes . Capacity is
limited only by current flash memory densities, although cost per megabyte
increases rapidly at higher capacities due to the expensive components.
flash drives have several advantages over other portable storage devices,
particularly the floppy disk. They are more compact, generally faster, hold more
data, and are considered more reliable (due to their lack of moving parts) 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.
The Flash Drive that is cool and wallet friendly
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.
The flash drive was first invented in 1998 by Dov Moran, President and CEO of
M-Systems Flash Pioneers (Israel). Dan Harkabi, who is now a Vice President at
SanDisk, led the development and marketing team at M-Systems. His most
significant contribution was that the product be self-reliant and free of the
need to install drivers. Nearly simultaneous development of similar products was
undertaken at Netac and at Trek 2000, Ltd. All three companies have similar and
disputed patents. IBM was the first North American seller of a USB flash drive,
and marketed an 8 MB version of the product in 2001 under the "Memory Key"
moniker. IBM later introduced a 16 MB version manufactured by Trek 2000, and
returned to M-Systems for the 64 MB version in 2003. Lexar can also lay claim to
a USB flash drive product. In 2000 they introduced a Compact Flash (CF) card
having an internal USB function. Lexar offered a companion card reader and USB
cable that eliminated the need for a USB hub.
The first flash drives were made by M-Systems and distributed in Europe under
the "disgo"  brand in sizes of
8 MB, 16 MB, 32 MB, and 64 MB. These were marketed as "a true floppy-killer",
and this design was continued up to 256 MB. Asian manufacturers soon started
making their own flash drives that were cheaper than the disgo series.
Modern flash drives have USB 2.0 connectivity. However, they do not currently
use the full 480 Mbit/s the specification supports due to technical limitations
inherent in NAND flash. The fastest drives available now use a dual channel
controller, though still fall considerably short of the transfer rate possible
from a current generation hard disk, or the maximum high speed USB 2.0
Flash drives have become iconic as a sort of "fashion statement"
, much like the iPod's white
ear bud headphones.
Internals of a typical flash drive
(Seitec brand USB1.1 pictured)
GNU Free Documentation License
||USB mass storage controller device
||Flash memory chip
||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
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
- Crystal oscillator - produces the device's main 12 MHz clock signal and
controls the device's data output through a phase-locked loop.
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
- 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.
Recently, USB flash drives have been integrated into other things such as a
watch or a pen.
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 standard.  
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- 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 host machine's data to be archived 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. 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.
- 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.
Data stored on flash drives are impervious to scratches and dust, and
flash drives are mechanically very robust making them suitable for
transporting data from place to place and keeping it readily at hand. Most
personal computers support USB as of 2009.
Flash drives also store data densely compared to many removable media. In
mid-2009, 256 GB drives became available, with the ability to hold many
times more data than a DVD or even a Blu-ray disc.
Compared to hard drives, flash drives use little power, have no fragile
moving parts, and for low capacities are small and light.
Flash drives implement the USB mass storage device class so that most
modern operating systems can read and write to them without installing
device drivers. 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 any file system or block addressing scheme. Some
computers can boot up from flash drives.
Some flash drives retain their memory even after being submerged in
water, even through a machine wash, although this is not a design feature
and not to be relied upon. 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. 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. All data on the other
removable storage devices tested, using optical or magnetic technologies,
Like all flash memory devices, flash drives can sustain only a limited
number of write and erase cycles before failure. 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) 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 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
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 key chains, necklaces and lanyards.
Compared to other portable storage devices, for example external hard
drives, USB flash drives have a high price per unit of storage and are only
available in comparatively small capacities; but hard drives have a higher
minimum price, so in the smaller capacities (16 GB and less), USB flash
drives are much less expensive than the smallest available hard drives.
Comparison to other portable memory forms
Flash storage devices are best compared to other common, portable, swappable
data storage devices: floppy disks, Zip disks, miniCD / miniDVD 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.
Floppy disks were the first publicly-popular method of file transport, but
have essentially become obsolete due to their low capacity, low speed, and low
durability. Virtually all new computers include USB ports, and many of them are
now sold without a floppy drive, the Apple iMac being the first to ship this
way. Floppy disks are still in use because of their low cost and ease of use
with older systems. Attempts to extend the floppy standard (such as the Imation
SuperDisk) were not successful because of a reputation for 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 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
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.
An original 16 megabyte "disgo"; The 8 MB version is
considered to be the first USB flash drive
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
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.
Recently, "USB flash drive" or simply "UFD" has emerged as the de facto
standard term for these devices. Many major manufacturers and resellers
(SanDisk, Lexar, Staples, Kingston, Wal*Mart) use UFD to describe them. However,
the myriad of different brand names and terminology used, in the past and
currently, makes UFDs more difficult for manufacturers to market and for
consumers to research. Some commonly used names are actually trademarks of
particular companies e.g. 'disgo'.
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.
- ^ Disgo Website. Retrieved on 2006-08-01.
- ^ "From Storage, a New Fashion", The New York
Times. Retrieved on 2006-08-01.
- ^ Opera@USB : Portable Opera for free. Retrieved
- ^ "WIZO-STICK-EP"-USB-MEMORY-FLASH-STICK. Retrieved
- ^ Kingmax Super Stick. Retrieved on 2006-08-01.