USB flash drive

A keydrive is essentially NAND-type Flash memory integrated with a USB interface used as a small, lightweight, removable data storage device. This hot-swappable, non-volatile, solid-state device is universally compatible with post Windows 98 platforms, Macintosh platforms, and most Unix-like platforms.

Keydrives are also known as “keychain drives”, “micro hard drives”, “pen drives”, “pocket drives”, “thumb drives”, “USB flash drives”, “USB flash memory drives”, “USB keys”, “USB memory keys”, “USB sticks”, "jump drives", “Piripicho” (primarily in Spanish), and “Kikinou” (primarily in French). They are also sometimes miscalled memory sticks (a Sony trademark describing a different type of portable memory).

A keydrive 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 keydrives feature the larger type-A USB connection, although some feature the smaller "miniUSB" connection.

These devices 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 (5V). To access the data stored in a keydrive, the keydrive must be connected to a computer, either by direct connection to the computer's USB port or via a USB hub.

Additional Features

Additionally many keydrives feature:

A light-emitting diode (or two) which flash to indicate that the device is connected, and which often flash a different pattern to indicate a write or read operation is underway.
Some supporting electronic components, needed to glue together the integrated circuits and to manage the power needed for USB communications and for writing to (and particularly erasing) flash memory.
A "write protect" switch, which stops the keydrive from being written to.

A number of manufacturers have chosen to make the appearance of the electronics within the keydrive a design feature, and so produce versions with transparent or translucent cases.

A cover or cap for the USB connector. This may improve the appearance of the keydrive and should also reduce the risk of damage due to static electricity travelling from the USB connector to the sensitive components inside. Originally in many keydrives this cap was separate from the main body and as such could easily be lost. In some cases, the cap contained the hole suitable for connection to a key chain or to otherwise aide transport and storage of device. However, this meant there was a risk of the main body being lost during transport. For these two reasons, most modern devices now connect the cap to the main body via some method. Some keydrives do not feature a cap but instead feature retractable USB connectors.

Pros and Cons

Keydrives 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.

Keydrives 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, keydrive 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 keydrives 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 keydrives 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.

Keydrives implement the USB mass storage device class, meaning that most modern operating systems can read and write to keydrives without any additional device drivers. Instead of exposing the complex technical detail of the underlying flash memory devices, the keydrives 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 keydrives, but that capability must be supported in the computer's BIOS, and (like other mass storage devices) the keydrive 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, keydrives can sustain only a limited number of write/erase cycles before failure. In normal use, mid-range keydrives 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 keydrive as a hard drive to run application software or an operating system. To address this (and the space limitations common on keydrives) some developers have produced versions of operating systems (such as Linux) or commonplace applications (such as the Mozilla Firefox) designed to run from keydrives. 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 keydrive).

The internal components of a typical keydrive

One end is fitted a single male type-A USB connector. Inside the plastic package is a small, highly cost-engineered, printed circuit board. On this is mounted some simple power circuity and a small number of surface-mounted integrated circuits (ICs). Typically one of these devices provides an interface to the USB port, another drives the onboard memory, and the other devices provide the flash memory storage themselves. 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 a typical keydrive consists largely of a single unified I/O chip and a generic flash memory part, and some manufacturers are planning yet more integrated devices, in which the storage and logic/communications functions are packaged in a single, ultra-low-cost device.

File:Cruzertitaniumusbkey.jpg

A titanium coated keydrive

The internal components of a typical keydrive
1	USB connector
2	USB mass storage controller device
3	test pins
4	flash memory device
5	crystal oscillator
6	LED
7	write-protect switch
8	unused space for second flash memory device

Template:Keydrive internals

Common uses of keydrives

Keydrives for network administration

Keydrives 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 keydrive is particularly useful for such uses, as it allows the system administrator to plug a keydrive containing anti-virus, spyware-removal, or trouble diagnosis software onto a suspect machine without risking the transmission of a virus or worm.

Keydrives for applications

Keydrives are also used to carry applications, which run on the host computer without requiring installation. The Mozilla Firefox browser has a configuration for keydrives. U3, backed by flash drive vendors, offers an API to keydrive-specific functions. airWRX is an application framework that runs from a keydrive, and turns its PC host and other nearby PCs into a multi-screen, web-like work environment.

Keydrives as Audio Players

Many companies make solid-state digital audio players (MP3 players) in a small Form factor, essentially producing keydrives with sound output and a rudimentary user interface. Others produce small solid-state mp3 players which contain a removable keydrive.

Keydrives and computer security

Some keydrives 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.

However, there is an application (Private Disk) which allows running without installation. Its executable file 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. Instructions on encrypting a USB flash disk.

Some manufacturers deploy physical authentication tokens in the form of a keydrive. 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 keydrive device is plugged into it. Some of these "PC lock" devices also function as normal keydrives when plugged into other machines.

Keydrives 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 keydrive 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 keydrives, 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.

Confusion over naming

The abundance of different names for these devices has often been a source of confusion. With no common agreed upon name, 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.

Lexar sells their usb memory sticks under the trademarked name jump drive and some use this term more generically in informal conversations. The term USB memory stick is also often used informally despite the fact memory stick is a Sony trademark.

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."

External links

Noncommercial GNU/Linux distributions for USB: