USB FLASH DRIVE

  

 USB flash drive, also known under a variety of other names is a data storage device that includes flash memory with an integrated Universal Serial Bus (USB) interface. USB flash drives are typically removable and rewritable, and physically much smaller than an optical disc. Most weigh less than 30 grams (1.1 oz). As of January 2013, drives of up to 512 gigabytes (GB) were available. A one-terabyte (TB) drive was unveiled at the 2013 Consumer Electronics Show and became available later that year. Storage capacities as large as 2 TB are planned, with steady improvements in size and price per capacity expected. Some allow up to 100,000 write/erase cycles, depending on the exact type of memory chip used, and have a 10-year shelf storage time.

USB flash drives are often used for the samepurposesfor which floppy disks or CDs were used, i.e., for storage, data back-up and transfer of computer files. They are smaller, faster, have thousands of times more capacity, and are more durable and reliable because they have no moving parts. Additionally, they are immune to electromagnetic interference (unlike floppy disks), and are unharmed by surface scratches (unlike CDs). Until about 2005, most desktop and laptop computers were supplied with floppy disk drives in addition to USB ports, but floppy disk drives have been abandoned due to their lower capacity compared to USB flash drives.

USB flash drives use the USB mass storage standard, supported natively by modern operating systems such as Windows, Linux, OS X and other Unix-like systems, as well as many BIOS boot ROMs. USB drives with USB 2.0 support can store more data and transfer faster than much larger optical disc drives like CD-RW or DVD-RW drives and can be read by many other systems such as the Xbox 360, PlayStation 3, DVD players and in a number of handheld devices such as smart phones and tablet computers, though the electronically similar SD card is better suited for those devices.

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 connection with a port on a personal computer, but drives for other interfaces also exist. USB flash drives draw power from the computer via the USB connection. Some devices combine the functionality of a digital audio player with USB flash storage; they require a battery only when used to play music.

History

Patent controversy

USB flash drives were invented by Amir Ban, Dov Moran and Oron Ogdan, all of the Israeli company M-Systems, who filed US patent 6148354 in April 1999. However, the patent describes a product that has a cable between the memory unit and the USB connector. Released later the same year, IBM Patent Disclosure RPS8-1999-0201 from September 13, 1999 by Shimon Shmueli accurately describes the USB flash drive. IBM partnered with M-Systems to bring the product to market. Shmueli was later an expert witness for M-Systems and as part of his testimony in the Singapore court presented the IBM disclosure and evidence to the fact that he invented the USB flash drive. M-Systems' product, developed by a team led by Dan Harkabi and named the Disk OnKey, was announced in September 2000.

Competing claims have been made by Singaporean company Trek Technology and Chinese company NetacTechnology, but these claims are based on patents that post-date M-Systems'. Both Trek Technology and Netac Technology have tried to protect their patent claims. Trek won a Singaporean suit, but a court in the United Kingdom revoked one of Trek's UK patents. While Netac Technology has brought lawsuits against PNY Technologies,^[  Lenovo, aigo ,Sony, and Taiwan's Acer and Tai Guen Enterprise Co,^[  most companies that manufacture USB flash drives do so without regard for Trek and Netac's patents.

  Pua Khein-Seng from Malaysia claims to have incorporated the world's first single chip USB flash controller. He is currently the CEO of Phis on Electronics Corp, which is based in Taiwan.

First commercial product

Trek Technology and IBM began selling the first USB flash drives commercially in 2000. Trek Technology sold a model under the brand name "ThumbDrive", and IBM marketed the first such drives in North America with its product named the "DiskOnKey", which was developed and manufactured by M-Systems. IBM's USB flash drive became available on December 15, 2000, and had a storage capacity of 8 MB, more than five times the capacity of the then-common floppy disks.

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.

Second generation

By 2013, most USB flash drives had USB 2.0 connectivity, which has 480 M bit/s as the transfer rate upper bound; after accounting for the protocol overhead that translates to a 35 MB/s effective throughput. That is considerably slower than what a hard disk drive or solid-state drive can achieve when connected via the SATA interface. Speeds may be given in megabytes per second (MB/s), megabits per second (Mbit/s), or in optical drive multipliers such as "180X" (180 times 150 KiB/s). File transfer speeds vary considerably among devices; typical fast drives from this generation claim to read at up to 30 MB/s and write at about half that speed, what is about 20 times faster than the theoretical speed USB 1.1 can achieve, which is limited to 12 Mbit/s (1 MB/s with accounted overhead).  The effective speed of a device is significantly affected by the data access pattern; for example, small writes to random locations are much slower (and cause more wear) than long sequential reads.

Third generation

Like USB 2.0 before it, USB 3.0 dramatically improved data transfer rates compared to its predecessor. It was announced in late 2008, but consumer devices were not available until the beginning of 2010. The USB 3.0 interface specifies transfer rates up to 5 Gbit/s (625 MB/s), compared to USB 2.0's 480 Mbit/s (60 MB/s).All USB 3.0 devices are backward compatible with USB 2.0 ports. As of April 2014, computers with USB 3.0 ports are common; most newer laptops and desktops have at least one such port. USB 3.0 port expansion cards are available to upgrade older systems, and many newer motherboards feature two or more USB 3.0 ports available through PCB headers.

Fourth generation

Starting March 2015, following the Apple Keynote, some manufacturers are announcing 3.1 type C USB keys. This new generation of USB keys, such as the PKparis K'isauve, have read/write speeds of 530 MB/s /520 MB/s.

Storage capacity

The first USB flash drive appeared on the market in late 2000, providing a storage capacity of 8 MB. Later, the maximum available storage capacity gradually doubled (16 MB, 32 MB, etc.) all the way up to reaching capacities of 512 GB and 1 TBby January 2013. However, as of May 2014 flash drives with anywhere from 8 to 128 GB are still frequently sold.

Design and implementation

Internals of a typical USB flash drive
1	USB Standard, Male A-plug
2	USB mass storage controller device
3	Test point
4	Flash memory chip
5	Crystal oscillator
6	LED (Optional)
7	Write-protect switch (Optional)
8	Space for second flash memory chip

On a USB flash drive, one end of the device is fitted with a single Standard-A USB plug; some flash drives additionally offer a micro USB plug, facilitating data transfers between different devices.^[36]

Inside the plastic casing is a small printed circuit board, which has some power circuitry and a small number of surface-mounted integrated circuits (ICs). Typically, one of these ICs provides an interface between the USB connector and the onboard memory, while the other is the flash memory. Drives typically use the USB mass storage device class to communicate with the host.