About Thumb USB Drives
USB flash drive
A SanDisk 16 GB USB retractable flash drive.A USB flash drive consists of flash memory data storage device integrated with a USB (Universal Serial Bus) 1.1 or 2.0 interface. USB flash drives are typically removable and rewritable, much smaller than a floppy disk, and most weigh less than 1 ounce (30 g). Storage capacities can range from a few megabytes to 256 GB[2] with steady improvements in size and price per capacity. Some allow 1 million write or erase cycles[3][4] and have 10-year data retention.
USB flash drives are often used for the same purposes as floppy disks were. They are smaller, faster, have thousands of times more capacity, and are more durable and reliable due to their lack of moving parts. Until approximately 2005, most PC and laptop computers were supplied with floppy disc drives, but most recent equipment has abandoned floppy disk drives in favor of USB ports.
Flash drives use the USB mass storage standard, supported natively by modern operating systems such as Windows, Mac OS X, Linux, and other Unix-like systems. USB drives with USB 2.0 support can store more data and transfer faster than a much larger optical disc drive and can be read by most other systems such as the Microsoft Xbox 360.
Nothing moves mechanically in a flash drive; the term drive persists because computers read and write flash-drive data using the same system commands as for a mechanical disk drive, with the storage appearing to the computer operating system and user interface as just another drive.[4] Flash drives are very robust mechanically, and can withstand anything that does not actually break the circuit board or connector.
A flash drive consists of a small printed circuit board carrying the circuit elements and a USB connector, insulated electrically and protected inside a plastic, metal, or rubberized case which can be carried in a pocket or on a key chain, for example. The USB connector may be protected by a removable cap or by retracting into the body of the drive, although it is not likely to be damaged if unprotected. Most flash drives use a standard type-A USB connection allowing plugging into a port on a personal computer, but drives for other interfaces also exist.
Most USB flash drives derive their power from the USB connection, and do not require a battery. Some devices which combine the functionality of a digital audio player with flash-drive-type storage require a battery for the player function.
Contents [hide]
1 Technology
2 History
2.1 First commercial product
2.2 Second generation
3 Design and implementation
3.1 Essential components
3.2 Additional components
3.3 Size and style of packaging
3.4 File system
4 Fake products
5 Uses
5.1 Personal data transport
5.2 Secure storage of data, application and software files
5.3 System administration
5.4 Application carriers
5.5 Computer forensics and law enforcement
5.6 Booting operating systems
5.7 Windows Vista and Windows 7 ReadyBoost
5.8 Audio players
5.9 Music storage and marketing
5.10 In arcades
5.11 Brand and product promotion
5.12 Backup
6 Advantages and disadvantages
6.1 Advantages
6.2 Disadvantages
7 Comparison with other portable storage
7.1 Tape
7.2 Floppy disk
7.3 Optical media
7.4 Flash memory cards
7.5 External hard disk
7.6 Obsolete devices
8 Security
8.1 Encryption
8.2 Security threats
8.3 Security breaches
9 Naming
10 Current and future developments
11 Flash drives for non-USB interfaces
12 See also
13 References
Technology
Main articles: Flash memory and USB
Flash memory combines a number of older technologies, with lower cost, lower power consumption and small size made possible by recent[update] advances in microprocessor technology. The memory storage was 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.
Hardware designers later developed EEPROMs with the erasure region broken up into smaller “fields” that could be erased individually without affecting the others. Altering the contents of a particular memory location involved copying the entire field into an off-chip buffer memory, erasing the field, modifying the data as required in the buffer, and re-writing it into the same field. 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 made semiconductor memory systems with serially accessed storage viable, and the simultaneous development of small, high-speed, low-power microprocessor systems allowed this to be incorporated into extremely compact systems. Serial access requires far fewer electrical connections for the memory chips than does parallel access, which has simplified the manufacture of multi-gigabyte drives.
Computers access modern[update] flash memory systems 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 players simply add extra software and a battery 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, for storing files of any type.
History
First commercial product
Trek Technology and IBM began selling the first USB flash drives commercially in 2000. Singaporean 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 manufactured by the Israeli company M-Systems). IBM’s USB flash drive became available on December 15, 2000,[6] and had a storage capacity of 8 MB, more than five times the capacity of the commonly used floppy disks (floppy disks having a capacity of 1.44MB).
In 2000 Lexar introduced a Compact Flash (CF) card with a USB connection, and a companion card read/writer and USB cable that eliminated the need for a USB hub.
On July 24, 2002 Netac Technology was granted a highly-contested Chinese patent for the USB flash drive.
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[8] that would be covered by Trek’s patent, but a court in the United Kingdom revoked[9] one of Trek’s patents in that country.
Second generation
Modern flash drives have USB 2.0 connectivity. However, they do not currently use the full 480 Mbit/s (60MB/s) the USB 2.0 Hi-Speed 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 vary considerably, and should be checked before purchase. Speeds may be given in Mbyte per second, Mbit per second, or optical drive multipliers such as “180X” (180 times 150 KiB per second). Typical fast drives claim to read at up to 30 megabytes/s (MB/s) and write at about half that. Older “USB full speed” 12 Mbit/s devices are limited to a maximum of about 1 MB/s.
Design and implementation
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 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.
Drives typically use the USB mass storage device class to communicate with the host.
Internals of a typical USB 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 (Optional)
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 microcontroller with 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 use a single printed circuit board for more than one storage size device.
USB connector cover or cap – reduces the risk of damage and prevents the ingress of fluff or other contaminants, and improves overall device appearance. Some flash drives use retractable USB connectors instead. Others have a swivel arrangement so that the connector can be protected without removing anything.
Transport aid – the cap or the body often contains a hole suitable for connection to a key chain or lanyard. Connecting the cap, rather than the body, can allow the drive itself to be lost.
Some drives offer expandable storage via an internal memory card slot, much like a memory card reader.
Size and style of packaging
Flash drives come in various, sometimes bulky or novelty, shapes and sizes, in this case ikura sushiSome 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 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 commonly-carried items such as watches, pens, and even the Swiss Army Knife; others have been fitted with novelty cases such as toy cars or LEGO bricks. The small size, robustness and cheapness of USB flash drives make them an increasingly popular peripheral for case modding.
Heavy or bulky flash drive packaging can make for unreliable operation when plugged directly into a USB port; this can be relieved by a USB extension cable. Such cables are USB-compatible, but do not conform to the USB standard.
File system
Main article: Flash file system
Most flash drives ship preformatted with the FAT or 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 maintenance utilities (e.g. ScanDisk) can be used to repair or retrieve corrupted data. However, because a flash drive appears as a USB-connected hard drive to the host system, the drive can be reformatted to any file system supported by the host operating system.
Defragmenting: Flash drives can be defragmented, but this brings little advantage as there is no mechanical head that moves from fragment to fragment. Flash drives often have a large internal sector size, so defragmenting means accessing fewer sectors. Defragmenting shortens the life of the drive by making many unnecessary writes.
Even Distribution: Some file systems are designed to distribute usage over an entire memory device without concentrating usage on any part (e.g., for a directory); this even distribution prolongs the life of simple flash memory devices. Some USB flash drives have this functionality built into the software controller to prolong device life, while others do not, therefore the end user should check the specifications of his device prior to changing the file system for this reason.
Hard Drive: Sectors are 512 bytes long, for compatibility with hard drives, and first sector can contain a Master Boot Record and a partition table. Therefore USB flash units can be partitioned as hard drives.
Fake products
Fake USB flash drives are fairly common. These are typically low capacity USB drives which are modified so that they emulate larger capacity drives (e.g. a 2GB drive being marketed as an 8GB drive). When plugged into a computer, they report themselves as being the larger capacity they were sold as, but when data is written to them, either the write fails, the drive freezes up, or it overwrites existing data. Software tools exist to check and detect fake USB drives.
Uses
USB flash drive with lanyard[edit] 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. In some cases a Secure USB Drive may use a hardware-based encryption mechanism that uses a hardware module instead of software for strongly encrypting 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. They are also used as a means to transfer recovery and antivirus software to infected PCs, allowing a portion of the host machine’s data to be archived. 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 applications that run on the host computer without requiring installation. While any standalone application can in principle be used this way, many programs store data, configuration information, etc. on the hard drive and registry of the host computer
The U3 company works with drive makers (parent company SanDisk as well as others) to deliver custom versions of applications designed for Microsoft Windows from a special flash drive; U3-compatible devices are designed to autoload a menu when plugged into a computer running Windows. Applications must be modified for the U3 platform not to leave any data on the host machine. U3 also provides a software framework for ISVs 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.
Similarly, other application virtualization solutions and portable application creators, such as VMware ThinApp (for Windows) or RUNZ (for Linux) can be used to run software from a flash drive without installation.
A wide range of portable applications which are all free of charge, and able to run off a computer running Windows without storing anything on the host computer’s drives or registry, can be found in the list of portable software.
Computer forensics and 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 digital evidence on computers confiscated from suspects.[15] Forensic software should not alter the information stored on the computer being examined in any way; other forensic suites run from CD-ROM or DVD-ROM, but cannot store data on the media they are run from (although they can write to other attached devices such as external drives or memory sticks).
Booting 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 and Windows 7 ReadyBoost
In Windows Vista and Windows 7, the ReadyBoost feature allows use of some flash drives to augment operating system memory (Windows Vista’s ReadyBoost capability, however, is limited to 4 GB of flash memory.)
Audio players
Many companies make small solid-state digital audio players, essentially producing flash drives with sound output and a simple user interface. Examples include the Creative MuVo, Philips GoGear and the iPod shuffle. Some of these players are true USB flash drives as well as music players; others do not support general-purpose data storage.
Many of the smallest players are powered by a permanently fitted rechargeable battery, charged from the USB interface.
Music storage and marketing
Digital audio files can be transported from one computer to another like any other file, and played on a compatible media player (with caveats for DRM-locked files). In addition, many home Hi-Fi and car stereo head units are now equipped with a USB port. This allows a USB flash drive containing media files in a variety of formats to be played directly on devices which support the format.
Artists have sold or given away USB flash drives, with the first instance believed to be in 2004 when the German band WIZO released the “Stick EP”, only as a USB drive. In addition to five high-bitrate MP3s, it also included a video, pictures, lyrics, and guitar tablature. Subsequently artists including Kanye West, Nine Inch Nails, Kylie Minogue[18] and Ayumi Hamasaki have released music and promotional material on USB 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. As of software revision (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.
In the arcade games Pump it Up NX2 and Pump it Up NXA, a special produced flash drive is used as a “save file” for unlocked songs, as well as progressing in the WorldMax and Brain Shower sections of the game.
In the arcade game Dance Dance Revolution X, an exclusive USB flash drive was made by Konami for the purpose of the link feature from its Sony PlayStation 2 counterpart.
Brand and product promotion
The availability of inexpensive flash drives has enabled them to be used for promotional and marketing purposes, particularly within technical and computer-industry circles (e.g. technology trade shows). They 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 awareness. The drive may be blank drive, or preloaded with graphics, documentation, web links, Flash animation or other multimedia, and free or demonstration software. Some preloaded drives are read-only; others are configured with a read-only and a writeable partition. Dual-partition drives are more expensive.
Flash drives can be set up to automatically launch stored presentations, websites, articles, and any other software immediately on insertion of the drive using the Microsoft Windows AutoRun feature.[20] Autorunning software this way does not work on all computers, and is normally disabled by security-conscious users.
Backup
Some value-added resellers are now using a flash drive as part of small-business turnkey solutions (e.g. 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 regularly updated. In either case, the drive is removed at night and taken offsite.
This is simple for the end-user, and more likely to be done;
The drive is small and convenient, and more likely to be carried off-site for safety;
The drives are less fragile mechanically and magnetically than tapes;
The capacity is often large enough for several backup images of critical data;
And flash drives are cheaper than many other backup systems.
It is also easy to lose these small devices, and easy for people without a right to data to take illicit backups.
Advantages and disadvantages
Advantages
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[update].
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, were destroyed.
Disadvantages
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)[25] 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 keychains, 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.