Keydrive

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 "keydrives", “pen drives”, “thumb drives”, “flash drives”, “USB keys”, “USB memory keys”, “USB sticks”, "jump drives", and many more names. 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.

Keydrives 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.

The keydrive was first invented in 1998 at IBM as a floppy drive replacement for the ThinkPad line of products. Although there is an IBM disclosure, they did not patent it. IBM later contracted M-Systems to develop and manufacture it non-exclusively. M-Systems holds the patent to this device as well as a few other related patents.

Keydrive Components

This photograph shows both sides of the printed circuit board inside a typical keydrive (circa 2004). The keydrive in this photograph is a 64 Mbyte USB2.0 device with its plastic case removed.

One end of the device is fitted a single male type-A USB connector. Inside the plastic casing is a small, highly cost-engineered, printed circuit board. Mounted on this board are some simple power circuity 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 provides the flash memory storage.

Essential Components

The parts of a typical keydrive are as follows:

• male type-A USB connector – provides an interface to the host computer. (item 1 in the diagram)
• USB mass storage controller – implements the USB host controller and provides a seamless linear interface to block-oriented serial flash devices while hiding the complexities of block-orientation, block erasure, and wear balancing. The controller contains a small RISC microprocessor and a small amount of ROM and RAM. (item 2 in the diagram)
• A NAND Flash memory chip – stores data. NAND flash is typically also used in digital cameras. (item 4 in the diagram)
• crystal oscillator – produces the device's main 12 MHz clock signal and controls the device's data output through phase-locked loop (item 5 in the diagram)

Additional Components

The typical device may also include:

• Jumpers and Test Pins – for testing during the keydrive's manufacturing. (item 3 in the diagram)
• LEDs – indicates data transfers or data reads and writes. (item 6 in the diagram)
• Write-Protect switch – indicates whether the device should be in "write-protection" mode. (item 7 in the diagram)
• unpopulated space – provides space to include a second memory chip. Having this second space allows the manufacturer to choose. (generally on a cost basis) whether to use one or two memory chips. (item 8 in the diagram)
• USB connector cover or cap – reduces the risk of damage due to static electricity, improves overall device appearance. Some keydrives do not feature a cap but instead feature retractable USB connectors.
• Transport aid – In some cases, the cap contained the hole suitable for connection to a key chain or to otherwise aid transport and storage of the USB flash device. However, this increases the risk of the device being lost during transport. For these reason, most devices now connect the cap to the main device body.

Strengths and Weaknesses

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).

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.

There are applications (TrueCrypt, Private Disk, etc.) which allow running without installation. The executable files 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.

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.

Naming Confusion

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.

AKA

• flash drives
• jump drives – Lexar sells their keydrives under this trademarked name
• keychain drives
• keydrives
• Kikinou (primarily in French)
• micro hard drives
• pen drives
• Piripicho (primarily in Spanish)
• pocket drives
• thumb drives
• USB flash drives
• USB flash memory drives
• USB keys
• USB memory keys
• USB memory stick – The term is also often used informally despite the fact memory stick is a Sony trademark.
• USB sticks

Keydrives vs Other Portable Memory

Flash storage devices are best compared to other common, portable, swappable data storage devices: floppy disks, zip disks, and CDs. Floppy and zip are each still available on the market as storage media despite their declining popularity. While 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 have essentially become obsolete due to their low capacity (1.44 MB) and their relatively low speed. Floppies were the first publicly-popular method of file transportation. Currently, very few systems may be purchased with a built-in floppy drive whereas very few systems may be purchased without a USB interface. Overall, the faster Flash memeory with its nearly universally available USB interface is more convenient than the ancient floppies. Floppy disks are still in use primarily because of their ease mounting into DOS and Linux systems.

Zip disks in many ways have gone the way of the floppy. Zip disks have capacities up to 250MB, but, like the floppy, zip drives are found buit-into systems rarely. Similarly, Zip is considered slower and more cumbersome than flash storage devices.

CD-R and CD-RW are another alternative for swappable storage media. Inverse to zip and floppy, CD burners are increasingly common in computer systems. While CDs are not suseptible to read/write wear (keydrives wear out after 10,000 read/write cycles), optical storage devices are slow. The major inconvenince that limits CDs over flash is the CD's inability to fit in a pocket or hang from a keychain.

share characteristics of magnetic tape, and, unlike zip and floppies, flash memory lacks moving parts, making them ideal as a simple solution, requireing only a port to interact with a system. The popularity of flash storage devices may be attributed to their compact size, multiple operating system compatibility, and their use of the standard USB interface.

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."

Future Developments

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 some manufacturers are planning to include more ICs the storage and logic/communications functions are packaged in a single, ultra-low-cost device.

See also

• USB Flash Drive Alliance
• Pocket hard drive
• Sneakernet

External links

Keydrive Applications

• Listing of USB keydrive applications
• airWRX: USB Keydrive application framework
• Freeware programs to run from a USB stick
• RUNT: ResNet Network Tester for USB Keydrives

Noncommercial GNU/Linux distributions for USB

• DamnSmallLinux (DSL), a small derivative of Knoppix, tailored to USB
• featherlinux – GNU/Linux distribution specifically created for USB sticks
• flash-puppy a mature distro designed for keydrives
• Flonix: USB Keydrive Operating System
• Generic Howto on USB booting, incl. with using a floppy/CD for the initial boot if the BIOS does not support USB
• Installing GNU/Debian Linux from an USB stick