SanDisk

3.4079341317883 (1336)
Posted by r2d2 03/01/2009 @ 08:04

Tags : sandisk, memory chips, semi conductors, technology

News headlines
SanDisk's Eli sings the Blu-Ray blues - Reuters Blogs
The flash memory business may be suffering its worst slump ever, but SanDisk CEO Eli Harari is carving tombstones for other businesses. The No.1 endangered technology, Harari said at the Reuters Global Technology Summit on Tuesday, is the Blu-Ray DVD....
SanDisk (SNDK) PriceWatch Alert Support Down To $13.58 - Market Intelligence Center
SanDisk (NasdaqNM: SNDK) closed yesterday at $14.73. So far the stock has hit a 52-week low of $5.07 and 52-week high of $32.66. SanDisk stock has been showing support around 13.58 and resistance in the 15.36 range. Technical indicators for the stock...
SanDisk Memory Stick PRO 256MB - CD Freaks.com
SanDisk Standard Memory Stick PRO and Memory Stick PRO Duo cards give you plenty of room to capture and store your world. And they're built to last, so you can be confident that all of your precious files will be there when you want them....
SanDisk Rallies; ThinkEquity Upgrades; NAND Prices Soar - Barron's Blogs
SanDisk (SNDK) shares are getting a lift this morning from ThinkEquity analyst Vijay Rakesh, who this morning upped his rating on the stock to Buy from Accumulate. He maintains a $19 target on the stock. Rakesh notes that NAND flash memory prices are...
Red Hat, SanDisk Gain as ... - InternetNews.com
By Paul Shread: More stories by this author: Stocks capped their worst week in two months on a down note Friday, but Red Hat (NYSE: RHT) and SanDisk (NASDAQ: SNDK) posted solid gains on analyst upgrades. Red Hat shares surged nearly 10% after Jefferies...
Gadget demand drives emissions - ITWeb
sandisk has added the sandisk Ultra Backup USB 2.0 portable flash drive to its long line of USB flash drives. This is the first to feature a solution to back up home or office data with the touch of a button, reports Grand Forks Herald....
SanDisk to Present at the 2009 JPMorgan Technology Conference - Business Wire (press release)
(BUSINESS WIRE)--SanDisk Corporation (Nasdaq:SNDK) today announced that Dr. Eli Harari, Chairman and CEO, will present to the investment community attending the 2009 JPMorgan Technology Media Telecom Conference in Boston on Monday, May 18,...
Are you using Micro SD cards yet? - Slippery Brick
I recently started using the micro SD cards from Sandisk after avoiding them forever. I just figured, they're so damn tiny, they had to be annoying. But after using them, I've found them pretty darn useful and even though they are obscenely tiny,...
SanDisk (SNDK) NewsBite - SNDK Is On the Move - Market Intelligence Center
SanDisk (SNDK) appears to be on the move today and is now at $12.87, down $0.57 (-4.24%) on volume of 1146112 shares traded. Over the last 52 weeks the stock has ranged from a low of $5.07 to a high of $33.17. SanDisk stock has been showing support...
Stocks Of The Day: SunPower Corp. (NASDAQ: SPWRA), SanDisk (NASDAQ ... - istockAnalyst.com (press release)
(NASDAQ: SPWRA), SanDisk (NASDAQ: SNDK) SunPower Corporation engages in the design, manufacture, and marketing of solar electric power technologies worldwide for residential, commercial and utility-scale power plant customers....

SanDisk

SanDisk Corporation (NASDAQ: SNDK) is an American multinational corporation which designs and markets flash memory card products. SanDisk was founded in 1988 by Eli Harari and Sanjay Mehrotra, non-volatile memory technology experts. SanDisk became a publicly traded company on NASDAQ in November 1995. In January 2008 its market capitalization was US$6.5 billion. SanDisk produces many different types of flash memory, including various memory cards and a series of USB removable drives. SanDisk markets to both the high-end and low-end sector demand for premium quality flash memory; and markets to other equipment makers as well as direct to consumers.

The company is headquartered in Milpitas, California, with offices or manufacturing facilities in 10 locations in Asia (including Taiwan, China and Japan), 6 locations in Europe (including the UK, Ireland and Spain), and 3 locations in Israel (Kfar Sava, Tefen and Omer).

Eli Harari, an Israeli Engineer, began making early contributions to EEPROM - electrically erasable programmable read-only memory, a precursor to flash memory. Harari worked on flash memory at Intel, leaving to found a start-up which failed. In 1988, Harari launched the company that would become SanDisk with former Intel colleague Sanjay Mehrotra, and former Hughes Microelectronics colleague Jack Yuan.

Early on, Sandisk had recognized that digital cameras would need digital storage, and computers could become ever more mobile and light and would require a similar storage technology. In 1988 Harari offered the flash memory card technology to Kodak for inclusion in their cameras. Kodak offered to fund the development with the condition that SanDisk offer a three year exclusive contract for the 'digital film'. Harari and Sandisk rejected the offer, preferring to have competition in the marketplace.

On September 4, 2006 at the IFA show in Berlin, German authorities seized all MP3 players that were in SanDisk's booth since Italian patent company Sisvel had won an injunction against it regarding the MP3 format. Sisvel, who had previously filed a separate lawsuit in Mannheim, claims that SanDisk uses the MP3 format without paying the required licensing fee. On September 8, 2006, a Berlin court overturned the injunction and SanDisk put the players back on display.

On March 16, 2007 SanDisk issued a press release announcing they had reached agreement and now acquired licences for all current and future MP3 applications.

FlashCP is a digital rights management technology for the storage of electronic materials (e.g. e-books) on portable devices. FlashCP is targeted primarily at students and allows transportation of copyrighted material while enforcing copy restrictions against the user. SanDisk acquired the technology in 2005 with the purchase of Israel-based MDRM. As an avid proponent of DRM, this is one of many such technologies developed by SanDisk, the other ones being Gruvi pre-loaded memory cards and the underlying TrustedFlash technology. SanDisk media players have near universal support for Windows Media DRM and rely almost exclusively on variants of the copy-protection capable Secure Digital format for removable storage.

Currently, SanDisk manufactures one drive that uses the FlashCP technology, called the Freedom Drive, which is part of the Cruzer line. Additionally, digital content can be downloaded to Cruzer Freedom from the SanDisk Plaza, a growing online store offering digital books, music, games, and education tools. Prices for on line products vary. Many selections are free. Once downloaded, the digital content may be used online and offline.

In addition, the company has a division named SanDisk Enterprise which develops and manufactures a secure USB drive. SanDisk Enterprise was created to provide a solution for enterprises and government agencies to allow mobilization of the corporate computing environment with password protected USB flash drives. The company attempts to address the organization's risk management needs.

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SanDisk Cruzer

The interior of the Cruzer Titanium.  1. Flash memory chip  2. USB A-type plug 3. Casing 4. Loop for lanyard 5. Microcontroller

The SanDisk Cruzer is a range of USB flash drives produced by SanDisk. These flash drives have a capacity range from 1 GB to 32 GB.

As of 2008, the line has seven flash drives. Most drives feature a retractable USB A-type plug. The other drives feature a cap. Current drives, except for some exceptions have U3 pre-installed.

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SanDisk Sansa

Sansa Clip connected to a USB hub.

The SanDisk Sansa is a line of flash memory-based digital audio players and portable media players produced by SanDisk.

The slotRadio player is a small, stylish, portable music device that comes bundled with a slotRadio™ card preloaded with 1,000 songs featuring artists from the Billboard® charts, and eaturing artists from the Billboard® charts, and arranged into a variety of genre-themed playlists. The die-cast aluminum player also features a 1.5" OLED screen for viewing artist and song information, a FM radio and even an integrated, handy belt clip for hands-free listening.

Introduced October 15, 2008, the slotMusic player was built specifically for the the playback of the slotMusic format. It does not ship with any storage of its own.

The Sansa Fuze, released on March 28, 2008 in capacities of 2, 4 & 8 GB, is a portable media player with a 1.9-inch color display and a thickness of 0.3 inches. It also features a 40-preset FM radio/recorder, a voice recorder, can record from FM, and has a 24-hour battery life on continuous audio playback. Storage is expandable via a microSDHC slot. The recent firmware update (1.01.22) enables FLAC and Ogg Vorbis playback, among with other improvements.

The redesigned Sansa View was announced on September 10, 2007, after the player was shelved three months earlier. On October 1, 2007, the player was released. The Sansa View resembles the players in the e200 series, although it is bigger (in fact, significantly taller) in dimensions. The player has a 2.4-inch QVGA screen and is available in capacities of 8 GB, 16 GB, and 32 GB, each with a microSD card slot for storage expansion. Unlike earlier Sansa players, the View supports such video formats as H.264, MPEG-4, and unencrypted WMV.

Also known as the m300, the Sansa Clip was released on October 9, 2007. The player is similar in size and concept to the second-generation iPod shuffle, but incorporates a removable clip and 4-line OLED screen (one line yellow, three blue.) The Clip has an FM tuner/recorder and a built-in microphone. The flash-based player ships in capacities of 1 GB (available only in black), 2 GB (available in black, blue, red and pink), and 4 GB (silver and black). In November 2008, black and silver 8GB versions were advertised in the UK. The 8GB version has been sold in Walmart stores in the U.S.A.

Firmware version 01.01.29, released in May 2008, enabled Ogg Vorbis compatibility for the Sansa Clip. The 01.01.30 firmware update improved OGG support and added FLAC support.

The Sansa Shaker is a screenless digital audio player and comes in colors of blue, red, white, and pink with an SD card slot. One 512 MB or 1 GB card is included, and cards up to 4 GB (non-SDHC) can be used. The tubular design is intended to be kid-friendly, and the player resembles a saltshaker, as it will randomly skip one, two or three songs when shaken. The Shaker plays up to 10 hours of continuous audio with a AAA battery, and has twin headphone jacks and a built-in speaker. The upper controller band adjusts volume and the lower controller band skips to next/previous song or fast forwards/rewinds the current song when hold. Unlike other players, the Shaker only supports audio files in MP3, and when the memory card is taken out during playback, the player will emit an "uh-oh" sound. When the player's memory card is put back in, it makes a popping noise.

The Sansa Express is a flash-based digital audio player in capacities of 1 GB and 2 GB. It has a built-in USB connector, similar to the first-generation iPod shuffle and a 1.1-inch, duochromatic OLED display, a microSDHC slot that works with up to 4GB capacities, an FM tuner, a microphone for voice recording and an internal Lithium-Ion battery. It is also able to record FM radio and voice on its internal memory. This player is not considered as a descendant of the c200 series, as it only plays audio. It is more similar to the m200 series and maintains much of its design and internal software structure.

The Sansa c200 has a removable, lithium-ion rechargeable battery, FM tuner/recorder, and built-in microphone. It also features a 1.4-inch color display and a microSD card slot. The players are compatible with many accessories which were originally made for the Sansa e200 series. The Sansa c200 series is available in 1 and 2 GB capacities. Newer models, referred to as v. 2, have different hardware that added support for the Audible file format 2. However, the v2 are not supported by Rockbox. The packaging of the new models has been updated with the line "Supports Audible audio file formats". The free software Rockbox firmware supports the Version 1 hardware and includes a number of additional features, including support for microSDHC which enables adding up to 16 GB of storage capacity.

The Sansa e200R was released in October 2006. Physically identical to the regular Sansa e200, this player is sold exclusively at Best Buy, or directly through Rhapsody. The player has a feature called "Rhapsody Channels", which is the online service's brand of podcasting, and also comes with pre-loaded content.

The Sansa Connect is a Wi-Fi-enabled player that allows the user to connect to any open network in the area. The Mono/Linux-based device has a 2.2-inch TFT LCD screen, but unlike SanDisk's previous player, the e200 series, the Sansa Connect does not have the ability to connect via USB mass storage or tune to FM radio yet. The player was developed by ZING Systems in collaboration with SanDisk and Yahoo!, which provides music streaming via LAUNCHcast radio and a subscription download service. Viewing pictures from Flickr is also possible with the device. The Sansa Connect is currently only available in the United States in capacities of 4 GB. The storage capacity is expandable with microSD cards, currently giving the player up to an extra 2 GB of storage. At the 2007 Consumer Electronics Show, the Sansa Connect won the Best of Show award. A new firmware update allows the player to support microSDHC cards up to a capacity of 8 GB and the playback of digital video.

The original View was SanDisk's attempt at a portable media player, and had a 4-inch screen, built-in speaker and an expansion slot for SDHC and SD cards. It was announced on the 2007 Consumer Electronics Show. On June 1, 2007, SanDisk announced that the player had been shelved. It has since been redesigned and launched.

The Sansa m200 series are digital audio players are have been released in four models: m230 (512MB), m240 (1 GB), m250 (2 GB), and m260 (4 GB). The players have a built-in FM tuner and microphone, and supports MP3, WMA, WAV and Audible (.aa) audio file formats. It comes in different colors (one for each memory size) such as blue, black, pink, and gray, and uses a single AAA battery for power. There were four different hardware revisions of this player. The first three revisions used a Telechips TCC770 SoC for a CPU and DSP, and the fourth using a chip developed by Austria Microsystems.

The e100 series is a monochromatic player with a blue backlight, FM tuner with 20 presets SRS WOW technology, an SD expansion slot capable of using cards up to 4 GB (non-SDHC), internal memory of 512 MB (e130) or 1 GB (e140), depending on the model, and uses a single AAA battery for power. It supports MP3, WMA and Audible file formats.

In May 2006, SanDisk launched an anti-iPod campaign labelling iPod users as "iSheep", "iChimps", etc. These campaigns featured graffiti-type posters around urban areas and a website (iDont.com), in an effort to promote the e200 series. SanDisk has since replaced the iDont campaign with LilMonsta.com, which is also the name of the creature that resembles the player. In June 2008, the LilMonsta.com was shutdown in favor of the new website.

On September 3rd, 2006 SanDisk announced the "Made for Sansa" program, following the similar program by Apple inc for its iPod. With it, a number of 3rd party accessories have been released, including hardware accessories mostly for the proprietary 30-pin IO port featured on the e200, c200, Connect, View, and Fuze players.

Maki Goto, a Japanese pop artist has also endorsed the Sansa e200 series with a promotional video, featuring one of her songs.

In 2007, SanDisk launched a Flash microsite to promote the line of MP3 players. ShopSansa.com (available only in North America, Australia and New Zealand) was later added as the official online store for the players, as well as third-party accessories and entertainment products such as console games and DVD movies.

The above features are subject to the platform limitations. Rockbox may lack some features of the official firmware (for example support for DRM-covered music) and may considerably change the player interface. Depending on the manufacturer and reseller, usage of Rockbox may actually void player warranty.

Ports are only available for Version 1 Sansa e200s (running firmware 01.XX.XX) and Sansa c200s.

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Flash memory

A flash memory cell.

Flash memory is a non-volatile computer memory that can be electrically erased and reprogrammed. It is a technology that is primarily used in memory cards and USB flash drives for general storage and transfer of data between computers and other digital products. It is a specific type of EEPROM (Electrically Erasable Programmable Read-Only Memory) that is erased and programmed in large blocks; in early flash the entire chip had to be erased at once. Flash memory costs far less than byte-programmable EEPROM and therefore has become the dominant technology wherever a significant amount of non-volatile, solid state storage is needed. Example applications include PDAs (personal digital assistants), laptop computers, digital audio players, digital cameras and mobile phones. It has also gained popularity in the game console market, where it is often used instead of EEPROMs or battery-powered SRAM for game save data.

Flash memory is non-volatile, which means that no power is needed to maintain the information stored in the chip. In addition, flash memory offers fast read access times (although not as fast as volatile DRAM memory used for main memory in PCs) and better kinetic shock resistance than hard disks. These characteristics explain the popularity of flash memory in portable devices. Another feature of flash memory is that when packaged in a "memory card," it is enormously durable, being able to withstand intense pressure, extremes of temperature, and even immersion in water.

Although technically a type of EEPROM, the term "EEPROM" is generally used to refer specifically to non-flash EEPROM which is erasable in small blocks, typically bytes. Because erase cycles are slow, the large block sizes used in flash memory erasing give it a significant speed advantage over old-style EEPROM when writing large amounts of data.

Flash memory (both NOR and NAND types) was invented by Dr. Fujio Masuoka while working for Toshiba circa 1980. According to Toshiba, the name "flash" was suggested by Dr. Masuoka's colleague, Mr. Shoji Ariizumi, because the erasure process of the memory contents reminded him of a flash of a camera. Dr. Masuoka presented the invention at the IEEE 1984 International Electron Devices Meeting (IEDM) held in San Francisco, California.

Intel saw the massive potential of the invention and introduced the first commercial NOR type flash chip in 1988. NOR-based flash has long erase and write times, but provides full address and data buses, allowing random access to any memory location. This makes it a suitable replacement for older ROM chips, which are used to store program code that rarely needs to be updated, such as a computer's BIOS or the firmware of set-top boxes. Its endurance is 10,000 to 1,000,000 erase cycles. NOR-based flash was the basis of early flash-based removable media; CompactFlash was originally based on it, though later cards moved to less expensive NAND flash.

Toshiba announced NAND flash at the 1987 International Electron Devices Meeting. It has faster erase and write times, and requires a smaller chip area per cell, thus allowing greater storage densities and lower costs per bit than NOR flash; it also has up to ten times the endurance of NOR flash. However, the I/O interface of NAND flash does not provide a random-access external address bus. Rather, data must be read on a block-wise basis, with typical block sizes of hundreds to thousands of bits. This made NAND flash unsuitable as a drop-in replacement for program ROM since most microprocessors and microcontrollers required byte-level random access. In this regard NAND flash is similar to other secondary storage devices such as hard disks and optical media, and is thus very suitable for use in mass-storage devices such as memory cards. The first NAND-based removable media format was SmartMedia, and many others have followed, including MultiMediaCard, Secure Digital, Memory Stick and xD-Picture Card. A new generation of memory card formats, including RS-MMC, miniSD and microSD, and Intelligent Stick, feature extremely small form factors. For example, the microSD card has an area of just over 1.5 cm², with a thickness of less than 1 mm; microSD capacities range from 64 MB to 16 GB, as of October 2008.

Despite the need for high programming and erasing voltages, virtually all flash chips today require only a single supply voltage, and produce the high voltages via on-chip charge pumps.

One limitation of flash memory is that although it can be read or programmed a byte or a word at a time in a random access fashion, it must be erased a "block" at a time. This generally sets all bits in the block to 1. Starting with a freshly erased block, any location within that block can be programmed. However, once a bit has been set to 0, only by erasing the entire block can it be changed back to 1. In other words, flash memory (specifically NOR flash) offers random-access read and programming operations, but cannot offer arbitrary random-access rewrite or erase operations. A location can, however, be rewritten as long as the new value's 0 bits are a superset of the over-written value's. For example, a nibble value may be erased to 1111, then written as 1110. Successive writes to that nibble can change it to 1010, then 0010, and finally 0000. In practice few algorithms take advantage of this successive write capability and in general the entire block is erased and rewritten at once.

Although data structures in flash memory cannot be updated in completely general ways, this allows members to be "removed" by marking them as invalid. This technique may need to be modified for multi-level devices, where one memory cell holds more than one bit.

Another limitation is that flash memory has a finite number of erase-write cycles. Most commercially available flash products are guaranteed to withstand around 100,000 write-erase-cycles, before the wear begins to deteriorate the integrity of the storage. The guaranteed cycle count may apply only to block zero (as is the case with TSOP NAND parts), or to all blocks (as in NOR). This effect is partially offset in some chip firmware or file system drivers by counting the writes and dynamically remapping blocks in order to spread write operations between sectors; this technique is called wear levelling. Another approach is to perform write verification and remapping to spare sectors in case of write failure, a technique called bad block management (BBM). For portable consumer devices, these wearout management techniques typically extend the life of the flash memory beyond the life of the device itself, and some data loss may be acceptable in these applications. For high reliability data storage, however, it is not advisable to use flash memory that would have to go through a large number of programming cycles. This limitation is meaningless for 'read-only' applications such as thin clients and routers, which are only programmed once or at most a few times during their lifetime.

The low-level interface to flash memory chips differs from those of other memory types such as DRAM, ROM, and EEPROM, which support bit-alterability (both zero to one and one to zero) and random-access via externally accessible address buses.

While NOR memory provides an external address bus for read and program operations (and thus supports random-access); unlocking and erasing NOR memory must proceed on a block-by-block basis. With NAND flash memory, read and programming operations must be performed page-at-a-time while unlocking and erasing must happen in block-wise fashion.

Reading from NOR flash is similar to reading from random-access memory, provided the address and data bus are mapped correctly. Because of this, most microprocessors can use NOR flash memory as execute in place (XIP) memory, meaning that programs stored in NOR flash can be executed directly without the need to first copy the program into RAM. NOR flash may be programmed in a random-access manner similar to reading. Programming changes bits from a logical one to a zero. Bits that are already zero are left unchanged. Erasure must happen a block at a time, and resets all the bits in the erased block back to one. Typical block sizes are 64, 128, or 256 KB.

Bad block management is a relatively new feature in NOR chips. In older NOR devices not supporting bad block management, the software or device driver controlling the memory chip must correct for blocks that wear out, or the device will cease to work reliably.

The specific commands used to lock, unlock, program, or erase NOR memories differ for each manufacturer. To avoid needing unique driver software for every device made, a special set of CFI commands allow the device to identify itself and its critical operating parameters.

Apart from being used as random-access ROM, NOR memories can also be used as storage devices by taking advantage of random-access programming. Some devices offer read-while-write functionality so that code continues to execute even while a program or erase operation is occurring in the background. For sequential data writes, NOR flash chips typically have slow write speeds compared with NAND flash.

NAND flash architecture was introduced by Toshiba in 1989. These memories are accessed much like block devices such as hard disks or memory cards. Each block consists of a number of pages. The pages are typically 512 or 2,048 or 4,096 bytes in size. Associated with each page are a few bytes (typically 12–16 bytes) that should be used for storage of an error detection and correction checksum.

While reading and programming is performed on a page basis, erasure can only be performed on a block basis. Another limitation of NAND flash is data in a block can only be written sequentially. Number of Operations (NOPs) is the number of times the sectors can be programmed. So far this number for MLC flash is always one whereas for SLC flash it is four.

NAND devices also require bad block management by the device driver software, or by a separate controller chip. SD cards, for example, include controller circuitry to perform bad block management and wear leveling. When a logical block is accessed by high-level software, it is mapped to a physical block by the device driver or controller. A number of blocks on the flash chip may be set aside for storing mapping tables to deal with bad blocks, or the system may simply check each block at power-up to create a bad block map in RAM. The overall memory capacity gradually shrinks as more blocks are marked as bad.

NAND relies on ECC to compensate for bits that may spontaneously fail during normal device operation. This ECC may correct as little as one bit error in each 2048 bits, or up to 22 bits in each 2048 bits. If ECC cannot correct the error during read, it may still detect the error. When doing erase or program operations, the device can detect blocks that fail to program or erase and mark them bad. The data is then written to a different, good block, and the bad block map is updated.

Most NAND devices are shipped from the factory with some bad blocks which are typically identified and marked according to a specified bad block marking strategy. By allowing some bad blocks, the manufacturers achieve far higher yields than would be possible if all blocks had to be verified good. This significantly reduces NAND flash costs and only slightly decreases the storage capacity of the parts.

When executing software from NAND memories, virtual memory strategies are often used: memory contents must first be paged or copied into memory-mapped RAM and executed there (leading to the common combination of NAND + RAM). A memory management unit (MMU) in the system is helpful, but this can also be accomplished with overlays. For this reason, some systems will use a combination of NOR and NAND memories, where a smaller NOR memory is used as software ROM and a larger NAND memory is partitioned with a file system for use as a nonvolatile data storage area.

NAND is best suited to systems requiring high capacity data storage. This type of flash architecture offers higher densities and larger capacities at lower cost with faster erase, sequential write, and sequential read speeds, sacrificing the random-access and execute in place advantage of the NOR architecture.

The ONFI group is supported by major NAND Flash manufacturers, including Hynix, Intel, Micron Technology, and Numonyx, as well as by major manufacturers of devices incorporating NAND flash chips.

A group of vendors, including Intel, Dell, and Microsoft formed a Non-Volatile Memory Host Controller Interface (NVMHCI) Working Group. The goal of the group is to provide standard software and hardware programming interfaces for nonvolatile memory subsystems, including the "flash cache" device connected to the PCI Express bus.

It is important to understand that these two are linked by the design choices made in the development of NAND flash. An important goal of NAND flash development was to reduce the chip area required to implement a given capacity of flash memory, and thereby to reduce cost per bit and increase maximum chip capacity so that flash memory could compete with magnetic storage devices like hard disks.

NOR and NAND flash get their names from the structure of the interconnections between memory cells. In NOR flash, cells are connected in parallel to the bit lines, allowing cells to be read and programmed individually. The parallel connection of cells resembles the parallel connection of transistors in a CMOS NOR gate. In NAND flash, cells are connected in series, resembling a NAND gate, and preventing cells from being read and programmed individually: the cells connected in series must be read in series.

When NOR flash was developed, it was envisioned as a more economical and conveniently rewritable ROM than contemporary EPROM, EAROM, and EEPROM memories. Thus random-access reading circuitry was necessary. However, it was expected that NOR flash ROM would be read much more often than written, so the write circuitry included was fairly slow and could only erase in a block-wise fashion; random-access write circuitry would add to the complexity and cost unnecessarily.

Because of the series connection and removal of wordline contacts, a large grid of NAND flash memory cells will occupy perhaps only 60% of the area of equivalent NOR cells (assuming the same CMOS process resolution, e.g. 130 nm, 90 nm, 65 nm). NAND flash's designers realized that the area of a NAND chip, and thus the cost, could be further reduced by removing the external address and data bus circuitry. Instead, external devices could communicate with NAND flash via sequential-accessed command and data registers, which would internally retrieve and output the necessary data. This design choice made random-access of NAND flash memory impossible, but the goal of NAND flash was to replace hard disks, not to replace ROMs.

The write endurance of SLC Floating Gate NOR flash is typically equal or greater than that of NAND flash, while MLC NOR & NAND Flash have similar Endurance capabilities. Example Endurance cycle ratings listed in datasheets for NAND and NOR Flash are provided.

Because of the particular characteristics of flash memory, it is best used with either a controller to perform wear-levelling and error correction or specifically designed flash file systems, which spread writes over the media and deal with the long erase times of NOR flash blocks. The basic concept behind flash file systems is: When the flash store is to be updated, the file system will write a new copy of the changed data over to a fresh block, remap the file pointers, then erase the old block later when it has time.

In practice, flash file systems are only used for "Memory Technology Devices" ("MTD"), which are embedded flash memories that do not have a controller. Removable flash memory cards and USB flash drives have built-in controllers to perform wear-levelling and error correction so use of a specific flash file system does not add any benefit. These removable flash memory devices use the FAT file system to allow universal compatibility with computers, cameras, PDAs and other portable devices with memory card slots or ports.

Multiple chips are often arrayed to achieve higher capacities for use in consumer electronic devices such as multimedia players or GPS. The capacity of flash chips generally follows Moore's Law because they are manufactured with many of the same integrated circuits techniques and equipment.

Consumer flash drives typically have sizes measured in powers of two (e.g. 512 MB, 8 GB). This includes SSDs as hard drive replacements, even though traditional hard drives tend to use decimal units. Thus, a 64 GB SSD is actually 64 × 10243 bytes. In reality, most users will have slightly less capacity than this available, due to the space taken by filesystem metadata.

In 2005, Toshiba and SanDisk developed a NAND flash chip capable of storing 1 GB of data using Multi-level Cell (MLC) technology, capable of storing 2 bits of data per cell. In September 2005, Samsung Electronics announced that it had developed the world’s first 2 GB chip.

In March 2006, Samsung announced flash hard drives with a capacity of 4 GB, essentially the same order of magnitude as smaller laptop hard drives, and in September 2006, Samsung announced an 8 GB chip produced using a 40 nanometer manufacturing process.

In January 2008 Sandisk announced availability of their 16 GB MicroSDHC and 32 GB SDHC Plus cards.

But there are still flash-chips manufactured with low capacities like 1 MB, e.g., for BIOS-ROMs.

Commonly advertised is the maximum read speed, NAND flash memory cards are much faster at reading than writing. As a chip gets worn out, its erase/program operations slow down considerably, requiring more retries and bad block remapping. Transferring multiple small files, smaller than the chip specific block size, could lead to much lower rate. Access latency has an influence on performance but is less of an issue than with their hard drive counterpart.

The speed is sometimes quoted in MB/s (megabytes per second), or as a multiple of that of a legacy single speed CD-ROM, such as 60x, 100x or 150x. Here 1x is equivalent to 150 kilobytes per second. For example, a 100x memory card gives 150 KB x 100 = 15000 KB/s = 14.65 MB/s.

Serial flash is a small, low-power flash memory that uses a serial interface, typically SPI, for sequential data access. When incorporated into an embedded system, serial flash requires fewer wires on the PCB than parallel flash memories, since it transmits and receives data one bit at a time. This may permit a reduction in board space, power consumption, and total system cost.

With the increasing speed of modern CPUs, parallel flash devices are often much slower than the memory bus of the computer they are connected to. Conversely, modern SRAM offers access times below 10 ns, while DDR2 SDRAM offers access times below 20 ns. Because of this, it is often desirable to shadow code stored in flash into RAM; that is, the code is copied from flash into RAM before execution, so that the CPU may access it at full speed. Device firmware may be stored in a serial flash device, and then copied into SDRAM or SRAM when the device is powered-up. Using an external serial flash device rather than on-chip flash removes the need for significant process compromise (a process that is good for high speed logic is generally not good for flash and vice-versa). Once it is decided to read the firmware in as one big block it is common to add compression to allow a smaller flash chip to be used. Typical applications for serial flash include storing firmware for hard drives, Ethernet controllers, DSL modems, wireless network devices, etc.

An obvious extension of flash memory would be as a replacement for hard disks. Flash memory does not have the mechanical limitations and latencies of hard drives, so the idea of a solid-state drive, or SSD, is attractive when considering speed, noise, power consumption, and reliability.

There remain some aspects of flash-based SSDs that make the idea unattractive. Most important, the cost per gigabyte of flash memory remains significantly higher than that of platter-based hard drives. Although this ratio is decreasing rapidly for flash memory, it is not yet clear that flash memory will catch up to the capacities and affordability offered by platter-based storage. Still, research and development is sufficiently vigorous that it is not clear that it will not happen, either.

There is also some concern that the finite number of erase/write cycles of flash memory would render flash memory unable to support an operating system. This seems to be a decreasing issue as warranties on flash-based SSDs are approaching those of current hard drives.

As of May 24, 2006, South Korean consumer-electronics manufacturer Samsung Electronics had released the first flash-memory based PCs, the Q1-SSD and Q30-SSD, both of which have 32 GB SSDs. Dell Computer introduced the Latitude D430 laptop with 32 GB flash-memory storage in July 2007 -- at a price significantly above a hard-drive equipped version.

At the Las Vegas CES 2007 Summit Taiwanese memory company A-DATA showcased SSD hard disk drives based on Flash technology in capacities of 32 GB, 64 GB and 128 GB. Sandisk announced an OEM 32 GB 1.8" SSD drive at CES 2007. The XO-1, developed by the One Laptop Per Child (OLPC) association, uses flash memory rather than a hard drive. As of June 2007, a South Korean company called Mtron claims the fastest SSD with sequential read/write speeds of 100 MB/80 MB per second.

Rather than entirely replacing the hard drive, hybrid techniques such as hybrid drive and ReadyBoost attempt to combine the advantages of both technologies, using flash as a high-speed cache for files on the disk that are often referenced, but rarely modified, such as application and operating system executable files. Also, Addonics has a PCI adapter for 4 CF cards, creating a RAID-able array of solid-state storage that is much cheaper than the hardwired-chips PCI card kind.

The ASUS Eee PC uses a flash-based SSD of 2 GB to 20 GB, depending on model. The Apple Inc. Macbook Air has the option to upgrade the standard hard drive to a 128 GB Solid State hard drive. The Lenovo ThinkPad X300 also features a built-in 64 GB Solid State Drive.

Sharkoon has devoloped a device that uses six SDHC cards in RAID-0 as an SSD alternative; users may use more affordable High-Speed 8GB SDHC cards to get similar or better results than can be obtained from traditional SSDs at a lower cost.

One source states that, in 2008, the flash memory industry includes about US$9.1 billion in production and sales. Apple Inc. is the third largest purchaser of flash memory, consuming about 13% of production by itself. Other sources put the flash memory market at a size of more than US$20 billion in 2006, accounting for more than eight percent of the overall semiconductor market and more than 34 percent of the total semiconductor memory market.

Due to its relatively simple structure and high demand for higher capacity, NAND Flash memory is the most aggressively scaled technology among electronic devices. The heavy competition among the top few manufacturers only adds to the aggression. Current projections show the technology to reach approximately 20 nm by around 2010. While the expected shrink timeline is a factor of two every three years per original version of Moore's law, this has recently been accelerated in the case of NAND flash to a factor of two every two years.

As the feature size of Flash memory cells reach the minimum limit (currently estimated ~20 nm), further Flash density increases will be driven by greater levels of MLC, possibly 3-D stacking of transistors, and process improvements. Even with these advances, it may be impossible to economically scale Flash to smaller and smaller dimensions. Many promising new technologies (such as FeRAM, MRAM, PMC, PCM, and others) are under investigation and development as possible more scalable replacements for Flash.

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CompactFlash

A 16-GB CompactFlash card installed in a 2.5" IDE port with adaptor

CompactFlash (CF) is a mass storage device format used in portable electronic devices. For storage, CompactFlash typically uses flash memory in a standardized enclosure.

The format was first specified and produced by SanDisk in 1994. The physical format is now used for a variety of devices.

CompactFlash became a popular storage medium for digital cameras. In recent years it has been widely replaced by smaller cards on the consumer end, but it is still a preferred format for D-SLR cameras, for its superior capacity and reliability.

There are two main subdivisions of CF cards, Type I (3.3 mm thick) and the thicker Type II (CF2) cards (5 mm thick). The CF Type II slot is used by Microdrives and some other devices. There are four main speeds of cards including the original CF, CF High Speed (using CF+/CF2.0), a faster CF 3.0 standard and a yet faster CF 4.0 standard that is being adopted as of 2007. The thickness of the CF card type is dictated by the preceding PCMCIA card type standard which was used for data storage in previous years.

CompactFlash was originally built around Intel's NOR-based flash memory, but it has switched over to NAND. CF is among the oldest and most successful formats, and has held on to a niche in the professional camera market especially well. It has benefited from having both a better cost to memory size ratio than other formats for much of its life, and generally having larger capacities available than other formats.

CF cards can be used directly in a PC Card slot with a plug adapter, used as an ATA (IDE) or PCMCIA storage device with a passive adapter or with a reader, or attached various other types of ports such as USB or FireWire. As some newer card types are smaller, they can be used directly in a CF card slot with an adapter. Formats which can be used this way include SD/MMC, Memory Stick Duo, xD-Picture Card in a Type I slot, and SmartMedia in a Type II slot, as of 2005. Some multi-card readers use CF for I/O as well.

Flash memory, regardless of format, can take only a limited number of erase/write cycles to a particular "sector" before that sector can no longer be written. Typically, the controller in a CompactFlash device attempts to prevent premature wearout of a sector by choosing the location for a piece of data at write time so as to spread out the writing over the device. This process is called wear levelling.

NOR-based flash has lower density than newer NAND-based systems, and CompactFlash is therefore the physically largest of the three memory card formats that came out in the early 1990s, the other two being Miniature Card (MiniCard) and SmartMedia (SSFDC). However, CF did switch to NAND type memory later on. The IBM Microdrive format implements the CF Type II interface, but is not solid-state memory.

CompactFlash defines a physical interface which is smaller than, but electrically identical to, the ATA interface. That is, it appears to the host device as if it were a hard disk. The CF device contains an ATA controller. CF devices operate at 3.3 volts or 5 volts, and can be swapped from system to system. CF cards with flash memory are able to cope with extremely rapid changes in temperature. Industrial versions of flash memory cards can operate at a range of −45 to +85 °C.

CF has managed to be the most successful of the early memory card formats, outliving Miniature Card, SmartMedia, and PC Card Type I in mainstream popularity. The memory card formats that came out in the late 1990s through the early 2000s (SD/MMC, various Memory Stick formats, xD-Picture Card, etc.) offered stiff competition. The new formats were significantly smaller than CF, in some cases by an even greater fraction than CF had been smaller than PC Card. These new formats would eventually dominate the memory card market for compact consumer electronic devices.

Flash memory devices are non-volatile and solid-state, and thus are more robust than disk drives. Cards consume around 5% of the power required by small disk drives and still have reasonable transfer rates of over 45 MB/s for the more expensive 'high speed' cards.

Card speed is usually specified in "x" ratings, e.g. 8x, 20x, 133x. This is the same system used for CD-ROMs and gives the data rate as a multiple of the data rate of the first CD-ROMs (i.e. the data rate of an audio CD). The base rate is 150 kB/s, so for example, 20x = 20 * 150 kB/s = 3.0 MB/s.

The following table lists some common ratings and their respective maximum transfer rates.

As of 2008, CompactFlash cards are generally available in capacities from about 512 MB to 100 GB, with perhaps the most popular choices in Europe and North America being between 1 GB and 16 GB. Lower capacity cards, below 512 MB, are becoming rare in stores as higher capacity cards are readily available at the same price. The largest CompactFlash cards commonly available currently are the 32 GB models from various manufacturers — SanDisk launched its 16 GB Extreme III card at the 2006 Photokina trade fair, Transcend announced its 32 GB card on January 15, 2008. Samsung launched 16, 32 and 64 GB CF cards soon after. Pretec announced 48 GB cards in January 2008 and 100GB cards in September. These cards, and almost all cards over 2 GB, require the host device to support the FAT32 file system (if the camera is using a FAT file system). The largest cards, however, are usually not among the fastest ones.

There are varying levels of compatibility among FAT32-compatible cameras. While any camera that is claimed to be FAT32-capable is expected to read and write to a FAT32-formatted card without problems, some cameras are tripped up by cards larger than 2 GB that are completely unformatted, while others may take longer time to apply a FAT32 format. For example, the FAT32-compatible Canon EOS-1Ds will format any unformatted card with FAT16, even ones larger than 2 GB.

Indeed, there is a FAT32 bottleneck because of the manner in which many digital cameras update the file system as they write photos to the card. Writing to a FAT32-formatted card generally takes a little longer than writing to a FAT16-formatted card with similar performance capabilities. For instance, the Canon EOS 10D will write the same photo to a FAT16-formatted 2 GB CompactFlash card somewhat faster than to a same speed 4 GB FAT32-formatted CompactFlash card, although the memory chips in both cards have the same write speed specification.

The cards themselves can of course be formatted with any type of file system such as JFS and can be divided into partitions as long as the host device can read them. CompactFlash cards are often used instead of hard drives in embedded systems, dumb terminals and various small form-factor PCs that are built for low noise output or power consumption. CompactFlash cards are often more readily available and smaller than purpose-built solid-state drives and can be used to obtain faster seek times than hard drives.

When CompactFlash was first being standardized, even full-sized hard disks were rarely larger than 4 GB in size, and so the limitations of the ATA standard were considered acceptable. However, CF cards since the original Revision 1.0 have been able to have capacities up to 137 GB. While the current revision 4.1 from 2004 works only in ATA mode, future revisions are expected to implement SATA.

A future versions of CompactFlash, known as CFast, will be based on the Serial ATA bus, rather than the Parallel ATA/IDE bus for which all previous CompactFlash are designed.

These cards will support a higher maximum transfer rate than current CompactFlash current. As of 2009, SATA supports transfer rates up to 300 MB/s, while PATA is limited to 133 MB/s using UDMA 6. However, few if any current flash memory device support speeds greater than 133 MB/s, and CFast cards will not be physically or electronically compatible with CF cards, requiring new card readers and new digital cameras to take advantage of them. CFast cards use a 7-pin SATA data connector (identical to the standard SATA connector), but a 17-pin power connector that appears incompatible with the standard 15-pin SATA power connector, so an adaptor will be required to connect CFast cards in place of standard SATA hard drives.

CFast cards are expected to reach market in late 2009. At CES 2009, Pretec showed a 32 GB CFast and announced that they should reach market within a few months.

The only difference between the two types is that the Type II devices are 5 mm thick while Type I devices are 3.3 mm thick. The vast majority of all Type II devices are Microdrives and other miniature hard drives. Flash based Type II devices are rare but a few examples do exist. Compact Flash - Secure Digital adapters usually are Type II. Even the largest capacity cards commonly available are Type I cards. Most card readers will read both formats, with the exception of some early CF based cameras or poorer quality USB card readers where the slot is too small. Various Manufacturers of 4GB Compact Flash cards such as Sandisk, Toshiba, Alcotek and Hynix have developed devices which support mainly type I slots. Some latest DSLR's also dropped Type II support.

Microdrives are tiny hard disks—about 25 mm (1 inch) wide—packaged with a CompactFlash Type II form factor and interface. They were developed and released in 1999 by IBM in a 170 megabyte capacity. IBM then sold its disk drive division, including the Microdrive trademark, to Hitachi in December 2002. There are now other brands of Microdrives (such as Seagate, Sony, etc), and, over the years, these have become available in increasing capacities (up to 8 GB as of late 2008).

While these drives fit into and work in any CF II slot, they draw more current (500 mA maximum) than flash memory (100 mA maximum) and so may not work in some low-power devices (for example, NEC HPCs). Being a mechanical device a Microdrive is more sensitive to physical shock and temperature changes than flash memory. But Microdrives are not subject to the write cycle limitation inherent to flash memory.

The popular iPod mini, Nokia N91, iriver H10 (5 or 6GB model) and the Rio Carbon use a CF Microdrive to store music.

There is extensive marketplace competition for sales of all brands of flash memory. As a result counterfeiting is quite widespread. Under their own brand, or while imitating another, unscrupulous flash memory card manufacturers may sell low-capacity cards formatted to indicate a higher capacity, or else use types of memory which are not intended for extensive rewriting.

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USB flash drive

USB flash drive with lanyard

A USB flash drive consists of a NAND-type flash memory data storage device integrated with a USB (universal serial bus) interface. USB flash drives are typically removable and rewritable, much smaller than a floppy disk (1 to 4 inches or 2.5 to 10 cm), and most USB flash drives weigh less than an ounce . Storage capacities typically range from 64 MB to 64 GB with steady improvements in size and price per gigabyte. Some allow 1 million write or erase cycles and have 10-year data retention, connected by USB 1.1 or USB 2.0.

USB flash drives offer potential advantages over other portable storage devices, particularly the floppy disk. They have a more compact shape, operate faster, hold much more data, have a more durable design, and operate more reliably due to their lack of moving parts. Additionally, it has become increasingly common for computers to be sold without floppy disk drives. USB ports, on the other hand, appear on almost every current mainstream PC and laptop. These types of 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 also operate faster than an optical disc drive, while storing a larger amount of data in a much smaller space.

Nothing actually moves 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.

A flash drive consists of a small printed circuit board protected inside a plastic, metal, or rubberised case, robust enough for carrying with no additional protection—in a pocket or on a key chain, for example. The USB connector is protected by a removable cap or by retracting into the body of the drive, although it is not liable to be damaged if exposed. Most flash drives use a standard type-A USB connection allowing plugging into a port on a personal computer.

Flash memory combines a number of older technologies, with the low cost, low power consumption and small size 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 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 first copying the entire field into an off-chip buffer memory, erasing the field, and then re-writing 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 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 for the first time made 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 also greatly reduced the number of electrical connections required for the memory chips, which has allowed the successful manufacture of multi-gigabyte 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).

Computers access modern 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 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 data.

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 December 15, 2000, and had a storage capacity of 8 MB, more than five times the capacity of the (at the time) commonly used 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.

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 that would be covered by Trek's patent, but a court in the United Kingdom revoked one of Trek's patents in that country.

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 megabytes or megabits 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 megabit/s devices are limited to a maximum of about 1 MB/s.

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 simple 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.

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 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 1.0 standard.

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.

Flash drives can be defragmented, but this brings little advantage as there is no mechanical head slowed down by having to move from fragment to fragment (flash drives often have very large internal sector size, especially when erasing so defragmenting means accessing fewer sectors to erase a file). Defragmenting shortens the life of the drive by making many unnecessary writes.

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 prolongs life of simple flash memory devices. Some USB flash drives, however, have this functionality built into the 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.

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.

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.

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.

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.

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, such as VMware ThinApp can be used to run software from a flash drive without installation.

A 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 is available from portableapps.com; unlike U3 programs which run from a special U3-compatible USB stick, the PortableApps menu will run from a standard device, and can also use the Windows AutoRun feature.

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. 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).

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.

In Windows Vista and the upcoming Windows 7, the ReadyBoost feature allows use of some flash drives to augment operating system memory.

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 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.

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 releasd 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 and Ayumi Hamasaki have released music and promotional material on USB flash drives.

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 21 (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, causing problems for some players.

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 autorun stored presentations, websites and articles immediately on insertion of the drive by saving a file called autorun.inf with an appropriate shell script in the root directory of the drive. Autoloading this way does not work on all computers; the U3 drives described above load more reliably.

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.

It is also easy to lose these small devices, and easy for people without a right to data to take illicit backups.

Flash drives are impervious to scratches and dust, and 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 2008.

Flash drives also store data densely compared to many removable media. In mid-2008, 64 GB drives became available, with the ability to hold many times more data than a DVD.

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.

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) 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 device, 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.

Audio tape cassettes are no longer used for data storage. High-capacity floppy discs (e.g. Imation SuperDisk), and other forms of drives with removable magnetic media such as the Iomega Zip and Jaz drives are now largely obsolete and rarely used.

The applications of current data tape cartridges hardly overlap those of flash drives: the drives and media are very expensive, have very high capacity, slower transfer speed than most other storage media, and store data sequentially, leading to very long access times. These devices are used for routine backup of large systems.

Floppy disks are rarely fitted to modern computers and are obsolete for normal purposes, although internal and external drives can be fitted if required. Floppy disks may be the method of choice for transferring data to and from very old computers without USB or boot from floppy disks, and so they are sometimes used to change the firmware on, for example, BIOS chips.

The various writable and rewritable forms of CD and DVD are portable storage media supported by the vast majority of computers as of 2008. CD-R, DVD-R, and DVD+R can be written to only once., RW varieties up to about 1,000 erase/write cycles, while modern NAND-based flash drives often last for 500,000 or more erase/write cycles. DVD-RAM discs are the most suitable optical discs for data storage involving much rewriting.

Optical storage devices are among the cheapest methods of mass data storage after the hard drive. They are slower than their flash-based counterparts. Standard 12 cm optical discs are larger than flash drives and more subject to damage. Smaller optical media do exist, such as business card CD-Rs which have the same dimensions as a credit card, and the slightly less convenient but higher capacity 8 cm recordable CD/DVDs. The small discs are more expensive than the standard size, and do not work in all drives.

Universal Disk Format (UDF) version 1.50 and above has facilities to support rewritable discs like sparing tables and virtual allocation tables, spreading usage over the entire surface of a disc and maximising life, but many older operating systems do not support this format. Packet-writing utilities such as DirectCD and InCD are available but produce discs that are not universally readable (although based on the UDF standard). The Mount Rainier standard addresses this shortcoming in CD-RW media by running the older file systems on top of it and performing defect management for those standards, but it requires support from both the CD/DVD burner and the operating system. Many drives made today do not support Mount Rainier, and many older operating systems such as Windows XP and below, and Linux kernels older than 2.6.2, do not support it (later versions do). Essentially CDs/DVDs are a good way to record a great deal of information cheaply and have the advantage of being readable by most standalone players, but they are poor at making ongoing small changes to a large collection of information. Flash drives' ability to do this is their major advantage over optical media.

Flash memory cards, e.g. Secure Digital cards, are available in various formats and capacities, and are used by many consumer devices. However, although virtually all PCs have USB ports allowing the use of USB flash drives, memory card readers are not usually supplied as standard (particularly with desktop computers), although card readers are available that read many common formats. Alternatively, USB card readers can be used with memory cards, however, this results in two pieces of portable equipment (card plus reader) rather than one. Nevertheless, many consumer devices cannot make use of USB flash drives (even if the device has a USB port) whereas the memory cards used by the devices can relatively easily be read by PCs (with the attachment of a card reader), thus offering flash memory cards some advantages over USB flash drives.

Particularly with the advent of USB, external hard disks have become widely available and inexpensive. As drive capacity increases, external hard disk drives cost less per megabyte than flash drives, and are available in much larger capacities. Some hard drives support alternative and faster interfaces than USB 2.0 (e.g. IEEE 1394 and eSATA). For writes and consecutive sector reads (for example, from an unfragmented file), most hard drives can provide a much higher sustained data rate than current NAND flash memory.

Unlike solid-state memory, hard drives are susceptible to damage by shock, e.g., a short fall, have limitations on use at high altitude, and, like all magnetic media, are vulnerable when exposed to strong magnetic fields, although shielded by their casing. Hard drives are usually larger and heavier than flash drives in terms of overall mass, although hard disks often weigh less per unit of storage. Hard disks also suffer from file fragmentation which can reduce access speed.

As highly portable media, USB flash drives are easily lost or stolen. Several measures can be used to prevent the data on lost USB flash drives from being accessed by unauthorized users. Some of these measures, such as password-protected encryption, are used on other storage mediums such as floppy disks, hard disk drives, and CD-ROMs in an attempt to keep data from falling into the wrong hands. However, as history has shown, any method of preventing unauthorized access is only secure until it has been compromised.

In addition to securing on-board data, USB flash drives are increasingly being called upon to protect the environments in which they are used. In particular, USB flash drives have been used to transfer malware and autorun worms, usually unbeknownst to their owners, which can then infect and wreck havoc upon an otherwise secure network.

All USB flash drives can have their contents encrypted using third party disk encryption software such as FreeOTFE and TrueCrypt, which can be used without installation. The executable files can be stored on the USB drive, together with the encrypted file image. The encrypted partition can then be accessed on any computer running the correct operating system, although it may require the user to have administrative rights on the host computer to access data.

Other flash drives allow the user to configure secure and public partitions of different sizes, and offer hardware encryption.

Newer flash drives support biometric fingerprinting to confirm the user's identity. As of mid-2005, this was a costly alternative to standard password protection offered on many new USB flash storage devices. Most fingerprint scanning drives rely upon the host operating system to validate the fingerprint via a software driver, often restricting the drive to Microsoft Windows computers. However, there are USB drives with fingerprint scanners which use controllers that allow access to protected data without any authentication.

Some manufacturers deploy physical authentication tokens in the form of a flash drive. These are used to control access to a sensitive system by containing encryption keys or, more commonly, communicating with security software on the target machine. The system is designed so the target machine will not operate except when the flash drive device is plugged into it. Some of these "PC lock" devices also function as normal flash drives when plugged into other machines.

Flash drives present a significant security challenge for large organizations. 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 flash drive to a free USB port and using malicious software such as keyboard loggers or packet sniffers. To prevent this, some Antivirus software companies have designed specific applications to protect computers from the spread of malware via USB flash drives.

Also it is possible to run a solution that has been specifically designed to run from a USB flash drive. This kind of solution prioritises the protection of the USB flash drives and protects any sensitive data contained on USB flash drives from infected malware residing on any computer that the USB flash drive is attached to.

Alternatively some organizations simply forbid the use of flash drives altogether, and some computers are configured to disable the mounting of USB mass storage devices by ordinary users; others use third-party software to control USB usage. In a lower-tech security solution, some organizations disconnect USB ports inside the computer or fill the USB sockets with epoxy.

By August 2008, "USB flash drive" or simply "UFD" had emerged as a de facto standard term for these devices, and most major manufacturers use similar wording on their packaging, although potentially confusing alternatives (such as memory stick) or USB memory key still occur. The myriad different brand names and terminology used, in the past and currently, make UFDs more difficult for manufacturers to market and for consumers to research. Some commonly-used names actually represent trademarks of particular companies, such as Cruzer, TravelDrive, ThumbDrive, and Disgo.

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 part-count and overall package-cost.

Flash drive capacities on the market increase continually. As of 2008 few manufacturers continue to produce models of 256 MB and smaller; and many have started to phase out 512 MB capacity flash memory. High-speed has become a standard for modern flash drives and capacities of up to 64 GB have come on the market.

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.

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Source : Wikipedia