USB flash drive
A USB flash drive is a NANDtype flash memory data storage device integrated with a USB universal serial bus connector. USB flash drives are typically removable and rewritable, much shorter than aUSB hub
To access the data stored in a flash drive, the drive must be connected to a USB port, either a host controller built into a computer, a USB hub, or some other device designed to access the data, such as an mp3 player with a USBin port. Flash drives are active only when plugged into a USB connection and draw all necessary power from the supply provided by that connection. Some flash drives, however, especially highspeed drives, may require more power than the limited amount provided by a buspowered USB hub, such as those built into some computer keyboards or monitors. These drives will not work unless plugged directly into a host controller i.e., the ports found on the computer itself or a selfpowered hub. Flash memory and USB Flash memory is actually a combination of a number of older technologies, with the low cost, low power consumption and small size being made possible by recent advances in microprocessor technology. The memory storage is based on earlier EPROM and EEPROM technologies. These had very limited capacity, were very slow for both reading and writing, required complex highvoltage drive circuitry, and could only be rewritten after erasing the entire contents of the chip. Later EEPROMS were developed where the erasure region was broken up into smaller "fields" that could be erased individually without affecting the others. Altering the contents of a particular memory location involved first copying the entire field into an offchip buffer memory, erasing the field, and then rewriting the data back into the same field, making the necessary alteration to the relevant memory location while doing so. This required considerable computer support, and PCBased 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 highspeed serial data interfaces such as USB for the first time made serially accessed storage memory systems viable, and the simultaneous development of small, highspeed, lowpower microprocessor systems allowed this to be incorporated into extremely compact systems. Serial access also greatly reduced the number of electrical connections required for the memory chips, which has allowed the successful manufacture of multigigabyte capacities. Every external electrical connection is a potential source of manufacturing failure, and with traditional manufacturing, a point is rapidly reached where the successful yield approaches zero. Modern flash memory systems are accessed 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 lowcost MP3 Players simply add extra software 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.First invention and sale
Several companies claim to have invented the USB flash drive. Trek was the first company to sell a USB flash drive ThumbDrive in early 2000. However, their patent does not describe the USB flash drive; rather, it describes a very broad family of storage devices which could include the USB flash drive. The Israeli company MSystems acquired by SanDisk in November 2006 had been working on a USB flash drive since 1998. They registered the domain www.diskonkey.com on October 12, 1999, indicating their intention to sell a product. In 2000 Dan Harkabi joined the MSystems team and led the development of DiskOnKey. The industrial design was done by Ziba and the product won the IDEA award in 2001. MSystems' patent rigorously describes the USB flash drive and its implementation. An IBM invention disclosure RPS819990201 Sept. 99 by Shimon Shmueli et al. is the earliest known document to describe the USBFD accurately and completely, and only the USBFD. MSystems manufactured the DiskOnKey for IBM, which in late 2000 was the first to sell the product in North America. The IBM 8 MB 8 MiB USB Memory Key became available December 15, 2000. Shmueli later founded KeyNetica, the first company to patent and develop the concept that mobile and smart storage devices are all one needs for mobile computing. Current implementors of the concept are U3 part of SanDisk, which also owns the original KeyNetica patent and Ceedo. Trek Technology claims it was first to conceive and create the ThumbDrive.. Trek holds patents for the ThumbDrive in Japan, Taiwan, South Korea, the United Kingdom, New Zealand and Singapore. Nevertheless, the ownership of the patent for this device has been widely disputed. According to The Straits Times' report, other companies started marketing similar devices. MSystems, which was listed on NASDAQ at the time, called its gadgets DiskOnKey and Diskey. Electec is MSystems' importer, and FE Global is its sole distributor in Singapore. Lexar can also lay claim to a pioneering 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. Trek sued the four companies for infringing its patent. They counterclaimed, asking that Trek's patent be revoked as it was invalid. The Singapore Court of Appeal confirmed the validity of Trek Technology's patent for its ThumbDrive, calling it "novel and inventive" in the decision published in The Straits Times. The citystate's highest court also quashed the plea of four companies—Israeli firm MSystems Flash Disk Pioneers, Electec, FE Global Electronics and Singaporebased Ritronics Components—and ordered them to stop selling similar devices. The decision is expected to have a ripple effect on other similar lawsuits which the Trek group has pending in Britain, Japan and Taiwan. At least one decision in the UK has addressed similar points as those addressed by the Singapore Court of Appeal, but the hearing officer reached a different conclusion from that of the Singapore Court of Appeal, and Trek's patent was revoked in the UK.Second generation
Toshiba TransMemory Flash Drive with cover on. Comes preinstalled with U3, allowing users to take their applications, fully installed and operational, to any desktop.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 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 are about 3 MB/s. The highest current overall file transfer speeds are about 1060 MB/s. Older, "full speed" 12 Mbit/s devices are limited to a maximum of about 1 MB/s.Size and style of packaging
Flash drives come in various, sometimes bulky or novelty, shapes and sizes, in this case ikura sushi, Some 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 tools commonly carried on one's person 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, robust nature and relatively low price of USB flash drives makes them an increasingly popular peripheral for case modding.Overweight or illfitting 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 USBcompatible, but do not conform to the USB 1.0 standard.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, ScanDisk can be used to repair or retrieve corrupted data. However, because a flash drive appears as a USBconnected hard drive to the host system, the drive can be reformatted to any file system supported by the host operating system. It is worth noting that while defragmentation utilities can be run against a flash drive, there is no point in doing so. Defragmentation is a process intended to optimize access to data on a drive with spinning platters and moving heads; however, since flash memory is truly randomaccess a read to an adjacent cell is no faster than a read from any other cell, there is no performance gain. Further, the flash controller abstracts the physical memory location used for a given "sector", so that the host machine doesn't really know the layout of the data. Finally, as the defragmentation process moves data around, attempting to optimize it, a small portion of the flash memory's wear life is consumed. Several specialized file systems, like JFFS2 and YAFFS, which have wear levelling and other features, have been developed for flash drives.
Future developments
Semiconductor corporations have worked to reduce the cost of the components in a flash drive by integrating various flash drive functions in a single chip, thereby reducing the partcount and overall package cost. Flash drive capacities on the market are continuously increasing. As of 2008, 256 MB and smaller capacity flash memory has been largely discontinued, and 512 MB capacity flash memory is being phased out. Highspeed is now a standard for modern flash drives and capacities of up to 64 GB are available. Lexar is attempting to introduce a USB FlashCard, which would be a compact USB flash drive intended to replace various kinds of flash memory cards. Pretec introduced a similar card, which also plugs into every USB port, but is just one quarter the thickness of the Lexar model SanDisk has a product called SD Plus, which is a SecureDigital card with a USB connector. SanDisk has also 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.