A USB flash drive. DDR SDRAM ( double data rate synchronous dynamic random access memory) is a class of memory Integrated circuit used in Computers It achieves nearly twice Static random access memory (SRAM is a type of Semiconductor memory where the word static indicates that unlike ''dynamic'' RAM (DRAM, it does not Z-RAM, short for " zero capacitor RAM " is a new type of Computer memory in development by Innovative Silicon Inc Twin Transistor RAM ( TTRAM) is a new type of Computer memory in development by Renesas The Williams tube or the Williams-Kilburn tube (after inventors Freddie Williams and Tom Kilburn) developed about 1946 or 1947 Genesis in radar The basic concept of the delay line originated with World War II Radar research as a system to reduce clutter from reflections from the ground Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is Computer memory that can retain the stored information A programmable read-only memory ( PROM) or field programmable read-only memory ( FPROM) is a form of digital memory where the setting of each bit is EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable An EPROM, or E rasable P rogrammable '''''R'''ead-'''O'''nly '''M'''emory'', is a type of memory chip that retains its EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable Ferroelectric RAM ( FeRAM or FRAM) is a Random access memory similar in construction to DRAM but uses a Ferroelectric layer instead Magnetoresistive Random Access Memory ( MRAM) is a non-volatile computer memory ( NVRAM) technology which has been under development since The programmable metallization cell, or PMC, is a new form of non-volatile Computer memory being developed at Arizona State University and Phase-change memory (also known as PCM, PRAM, PCRAM, Ovonic Unified Memory, Chalcogenide RAM and C-RAM) is a type This article is about the music device manufacturer For the computer memory system see SONOS. Resistive random-access memory ( RRAM) is a new Non-volatile memory type being developed by Fujitsu, Sharp, Samsung, Micron IBM Racetrack Memory is an experimental Non-volatile memory device under development at IBM 's Almaden Research Center by a team led by Stuart Nano-RAM is a proprietary Computer memory technology from the company Nantero. Drum memory is a magnetic Data storage device and was an early form of Computer memory widely used in the 1950s and into the 1960s invented by Gustav Tauschek Magnetic core memory, or ferrite-core memory, is an early form of Random access Computer memory. Prehistory twistor memory Bubble memory is largely the brainchild of a single person Andrew Bobeck. Twistor is a form of Computer memory, similar to Core memory, formed by wrapping or closing Magnetic tape around a current-carrying wire The chip on the left is the flash memory. The microcontroller is on the right. A microcontroller (also MCU or µC is a functional Computer system-on-a- chip.

Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed. Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is Computer memory that can retain the stored information Computer data storage, often called storage or memory, refers to Computer components devices and recording media that retain digital 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. A memory card or flash memory card is a solid-state electronic Flash memory Data storage device used with Digital 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. EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable 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. A digital audio player, more commonly referred to as an MP3 player, is a Consumer electronics device that stores organizes and plays audio files Some Many compact digital still cameras can record Sound and moving Video as well as still Photograph. 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. EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable Static random access memory (SRAM is a type of Semiconductor memory where the word static indicates that unlike ''dynamic'' RAM (DRAM, it does not

Flash memory is non-volatile, which means that no power is needed to maintain the information stored in the chip. Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is Computer memory that can retain the stored information 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. Access time is the time delay or latency between a request to an electronic system and the access being completed or the requested data returned A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device 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. EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable 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. EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable

History

Flash memory (both NOR and NAND types) was invented by Dr. Fujio Masuoka while working for Toshiba in 1984. Dr is the inventor of Flash memory. He joined Toshiba in 1971 ( is a multinational conglomerate manufacturing company headquartered in Tokyo, Japan. 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. A flash is a device used in Photography that produces an instantaneous flash of artificial Light Dr. Masuoka presented the invention at the IEEE 1984 International Electron Devices Meeting (IEDM) held in San Francisco, California. The Institute of Electrical and Electronics Engineers or IEEE (read eye-triple-e) is an international Non-profit, professional organization 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. In Computer science, random access (sometimes called direct access) is the ability to access an arbitrary element of a sequence in equal time 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. In Computing, the BIOS (ˈbaɪoʊs In Computing, firmware is a computer program that is Embedded in a hardware device for example a Microcontroller. A set-top box (STB or set-top unit (STU is a device that connects to a Television and an external source of signal, turning the signal into 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. CompactFlash ( CF) is a Mass storage device format used in portable electronic devices

Toshiba announced NAND flash at ISSCC in 1989. ( is a multinational conglomerate manufacturing company headquartered in Tokyo, Japan. International Solid-State Circuits Conference is a global forum for presentation of advances in solid-state circuits and Systems-on-a-Chip. 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. Computer data storage, often called storage or memory, refers to Computer components devices and recording media that retain digital A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device A memory card or flash memory card is a solid-state electronic Flash memory Data storage device used with Digital The first NAND-based removable media format was SmartMedia, and many others have followed, including MultiMediaCard, Secure Digital, Memory Stick and xD-Picture Card. SmartMedia is a flash Memory card standard owned by Toshiba, with capacities ranging from 0 The MultiMediaCard ( MMC) is a Flash memory Secure Digital ( SD) is a non-volatile Memory card format developed by Matsushita, SanDisk, and Toshiba for use in Memory Stick is a removable flash Memory card format launched by Sony in October 1998, and is also used in general to describe the whole family The xD-Picture Card is a type of flash Memory card, used mainly in Digital cameras xD originally stood for e' x' treme D igital A new generation of memory card formats, including RS-MMC, miniSD and microSD, and Intelligent Stick, feature extremely small form factors. The MultiMediaCard ( MMC) is a Flash memory The miniSD Card is a small Form factor removable and portable memory device intended for use in cell phones / mobile phones, digital cameras microSD is a format for removable Flash memory cards It is derived from SanDisk TransFlash and is used mainly in mobile " Intelligent Stick " is a brand name for a USB flash drive Memory card which was developed by the 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 64MB to 16GB, as of March 2008. International holidays March 2 - Mothering Sunday (Britain March 7 - Nyepi (Indonesia

Principles of operation

Flash memory stores information in an array of memory cells made from floating-gate transistors. The floating gate transistor is a kind of Transistor that is commonly used for Non-volatile storage such as flash, EPROM and EEPROM In traditional single-level cell (SLC) devices, each cell stores only one bit of information. Some newer flash memory, known as multi-level cell (MLC) devices, can store more than one bit per cell by choosing between multiple levels of electrical charge to apply to the floating gates of its cells. In Electronics, a multi-level cell (MLC is a memory element capable of storing more than a single bit of information

A flash memory cell.

NOR flash

Programming a NOR memory cell (setting it to logical 0), via hot-electron injection.

Erasing a NOR memory cell (setting it to logical 1), via quantum tunneling.

In NOR gate flash, each cell resembles a standard MOSFET, except the transistor has two gates instead of one. Symbols There are two symbols for NOR gates the American ('military' symbol and the IEC ('European' or 'rectangular' symbol The metal–oxide–semiconductor field-effect transistor ( MOSFET, MOS-FET, or MOS FET) is a device used to amplify or switch electronic signals On top is the control gate (CG), as in other MOS transistors, but below this there is a floating gate (FG) insulated all around by an oxide layer. An oxide is a Chemical compound containing at least one Oxygen atom as well as at least one other element The FG is interposed between the CG and the MOSFET channel. The metal–oxide–semiconductor field-effect transistor ( MOSFET, MOS-FET, or MOS FET) is a device used to amplify or switch electronic signals Because the FG is electrically isolated by its insulating layer, any electrons placed on it are trapped there and, under normal conditions, will not discharge for many years. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J When the FG holds a charge, it screens (partially cancels) the electric field from the CG, which modifies the threshold voltage (V_T) of the cell. Screening is the damping of Electric fields caused by the presence of mobile charge carriers In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can The threshold voltage of a MOSFET is usually defined as the gate voltage where an inversion layer forms at the interface between the insulating layer (oxide and the substrate During read-out, a voltage is applied to the CG, and the MOSFET channel will become conducting or remain insulating, depending on the V_T of the cell, which is in turn controlled by charge on the FG. Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical The current flow through the MOSFET channel is sensed and forms a binary code, reproducing the stored data. Debt AIDS Trade in Africa (or DATA) is a Multinational non-government organization founded in January 2002 in London by U2 's In a multi-level cell device, which stores more than one bit per cell, the amount of current flow is sensed (rather than simply its presence or absence), in order to determine more precisely the level of charge on the FG. A bit is a binary digit, taking a value of either 0 or 1 Binary digits are a basic unit of Information storage and communication

A single-level NOR flash cell in its default state is logically equivalent to a binary "1" value, because current will flow through the channel under application of an appropriate voltage to the control gate. A NOR flash cell can be programmed, or set to a binary "0" value, by the following procedure:

• an elevated on-voltage (typically >5 V) is applied to the CG
• the channel is now turned on, so electrons can flow from the source to the drain (assuming an NMOS transistor)
• the source-drain current is sufficiently high to cause some high energy electrons to jump through the insulating layer onto the FG, via a process called hot-electron injection

To erase a NOR flash cell (resetting it to the "1" state), a large voltage of the opposite polarity is applied between the CG and drain, pulling the electrons off the FG through quantum tunneling. Hot carrier injection is the phenomenon in solid state devices or Semiconductors where either an Electron or a "hole" gains sufficient In Quantum mechanics, quantum tunnelling is a nanoscopic phenomenon in which a particle violates the principles of Classical mechanics by penetrating a Modern NOR flash memory chips are divided into erase segments (often called blocks or sectors). The erase operation can only be performed on a block-wise basis; all the cells in an erase segment must be erased together. Programming of NOR cells, however, can generally be performed one byte or word at a time.

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. A charge pump is an Electronic circuit that uses Capacitors as energy storage elements to create either a higher or lower Voltage power source

NOR flash memory wiring and structure on silicon

NAND flash

NAND gate flash uses tunnel injection for writing and tunnel release for erasing. Definition The NAND operation is a Logical operation on two Logical values typically the values of two Propositions that produces a value Tunnel injection is the Quantum tunneling effect also called Fowler-Nordheim tunnel injection, when Charge carriers are injected to an electric conductor Tunnel injection is the Quantum tunneling effect also called Fowler-Nordheim tunnel injection, when Charge carriers are injected to an electric conductor NAND flash memory forms the core of the removable USB storage devices known as USB flash drives, as well as most memory card formats available today. A memory card or flash memory card is a solid-state electronic Flash memory Data storage device used with Digital

NAND flash memory wiring and structure on silicon

Industry

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. Apple Inc, ( formerly Apple Computer Inc, is an American Multinational corporation with a focus on designing and manufacturing Consumer electronics ^[1] Other sources put the flash memory market at a size of more than US$20 billion dollars in 2006, accounting for more than eight percent of the overall semiconductor market and more than 34 percent of the total semiconductor memory market. ^[2]

Limitations

Block erasure

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. A nibble (often nybble) is the Computing term for a four- Bit aggregation or half an octet (an octet being an 8-bit Byte Successive writes to that nibble can change it to 1010, then 0010, and finally 0000. In practice few algorithms can 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 must be modified somewhat for multi-level devices, where one memory cell holds more than one bit.

Memory wear

Another limitation is that flash memory has a finite number of erase-write cycles (most commercially available flash products are guaranteed to withstand 100,000 write-erase-cycles for block 0, and no guarantees for other blocks). ^[3] This effect is partially offset by some chip firmware or file system drivers by counting the writes and dynamically remapping the blocks in order to spread the write operations between the sectors; this technique is called wear levelling. Wear levelling (also written wear leveling) is a technique for prolonging the Service life of some kinds of erasable Computer storage media such as 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 has been through a large number of programming cycles. This limitation does not apply to 'read-only' applications such as thin clients and routers, which are only programmed once or at most a few times during their lifetime. A thin client (sometimes also called a lean or slim client) is a client computer or client software in Client-server architecture networks A router ('rautər in the USA 'rutər in the UK and Ireland, or either pronunciation in Australia and Canada is a Computer whose software and hardware are usually

Low-level access

The low-level interface to flash memory chips usually differs from those of other common types such as DRAM, ROM, and EEPROM, which support random-access via externally accessible address buses. EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable In Computer science, random access (sometimes called direct access) is the ability to access an arbitrary element of a sequence in equal time An address bus is a Computer bus, controlled by CPUs or DMA -capable Peripherals for specifying the Physical addresses of computer

While NOR memory provides an external address bus for read operations (and thus supports random-access), unlocking, erasing, and writing NOR memory must proceed on a block-by-block basis. Typical block sizes are 64, 128, or 256 bytes. With NAND flash memory, all operations must be performed in a block-wise fashion: reading, unlocking, erasing, and writing.

NOR memories

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 copy them into RAM. In Computer science, execute in place (XIP is a method of executing programs directly from long term storage rather than copying it into RAM. NOR flash chips lack intrinsic bad block management, so when a flash block is worn out, the software or device driver controlling the device must handle this, or the device will cease to work reliably. In computing a device driver or software driver is a Computer program allowing higher-level computer programs to interact with a Hardware device

When unlocking, erasing or writing NOR memories, special commands are written to the first page of the mapped memory. These commands are defined by the Common Flash memory Interface (CFI) and the flash chips can provide a list of available commands to the physical driver. The Common Flash memory Interface ( CFI) is an open standard jointly developed by AMD, Intel, Sharp and Fujitsu.

Apart from being used as random-access ROM, NOR memories can also be used as storage devices. However, NOR flash chips typically have slow write speeds compared with NAND flash.

NAND memories

NAND flash architecture was introduced by Toshiba in 1989. ( is a multinational conglomerate manufacturing company headquartered in Tokyo, Japan. These memories are accessed much like block devices such as hard disks or memory cards. In Computing (specifically data transmission and data storage) block is a sequence of Bytes or Bits having a nominal length (a block size A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device A memory card or flash memory card is a solid-state electronic Flash memory Data storage device used with Digital Each block consists of a number of pages. The pages are typically 512 or 2,048 or 4,096 bytes in size. A byte (pronounced "bite" baɪt is the basic unit of measurement of information storage in Computer science. 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. In Mathematics, Computer science, Telecommunication, and Information theory, error detection and correction has great practical importance in A checksum is a form of Redundancy check, a simple way to protect the integrity of data by detecting errors in data that are sent through space ( Telecommunications

Typical block sizes include:
32 pages of 512 bytes each for a block size of 16 kiB
64 pages of 2,048 bytes each for a block size of 128 kiB
64 pages of 4,096 bytes each for a block size of 256 kiB
128 pages of 4,096 bytes each for a block size of 512 kiB

While programming is performed on a page basis, erasure can only be performed on a block basis. A kibibyte (a contraction of ki lo bi nary byte) is a unit of Information or Computer storage, established by the International 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 4.

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. Wear levelling (also written wear leveling) is a technique for prolonging the Service life of some kinds of erasable Computer storage media such as When a logical block is accessed by high-level software, it is mapped to a physical block by the device driver or controller, and a number of blocks on the flash chip are set aside for storing mapping tables to deal with bad blocks. The overall memory capacity gradually shrinks as more blocks are marked as bad.

The error-correcting and detecting checksum will typically correct an error where one bit per 256 bytes (2,048 bits) is incorrect. A checksum is a form of Redundancy check, a simple way to protect the integrity of data by detecting errors in data that are sent through space ( Telecommunications A bit is a binary digit, taking a value of either 0 or 1 Binary digits are a basic unit of Information storage and communication When this happens, the block is marked bad in a logical block allocation table, and its undamaged contents are copied to a new block and the logical block allocation table is altered accordingly. If more than one bit out of 2,048 is corrupted, the contents are partly lost, i. e. it is no longer possible to reconstruct the original contents. If this is detected when the block is written, the contents may still be available.

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 were tested good. This significantly reduces NAND flash costs and only slightly decreases the storage capacity of the parts.

The first physical block (block 0) is always guaranteed to be readable and free from errors. Hence, all vital pointers for partitioning and bad block management for the device must be located inside this block (typically a pointer to the bad block tables etc). If the device is used for booting a system, this block may contain the master boot record. MBRs and disk partitioning MBRs and system bootstrapping On IA-32 IBM PC compatible machines using the MBR Partition Table scheme the bootstrapping

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. Virtual memory is a Computer system technique which gives an application program the impression that it has contiguous working memory while in fact it may be physically In Computer Operating systems that have their Main memory divided into pages, paging (sometimes called swapping) is a transfer A memory management unit (MMU) in the system is helpful, but this can also be accomplished with overlays. A memory management unit ( MMU) sometimes called paged memory management unit ( PMMU) is a Computer hardware component responsible for handling In a general computing sense overlaying means "replacement of a block of stored instructions or data with another" Overlaying is a programming method that allows programs 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 random access storage area. In Computing, a file system (often also written as filesystem) is a method for storing and organizing Computer files and the data they contain to make NAND is best suited to flash devices requiring high capacity data storage. This type of flash architecture combines higher storage space with faster erase, write, and read capabilities over the execute in place advantage of the NOR architecture.

Standardization

A group called the Open NAND Flash Interface Working Group (ONFI) has developed a standardized low-level interface for NAND flash chips. The Open NAND Flash Interface Working Group, or ONFI, is a Consortium of technology companies working to develop Open standards for NAND This allows interoperability between conforming NAND devices from different vendors. The ONFI specification version 1. 0^[4] was released on December 28, 2006. It specifies:

• a standard physical interface (pinout) for NAND flash in TSOP-48, WSOP-48, LGA-52, and BGA-63 packages
• a standard command set for reading, writing, and erasing NAND flash chips
• a mechanism for self-identification (comparable to the Serial Presence Detection feature of SDRAM chips)

The ONFI group is supported by major NAND flash manufacturers, including Intel, Micron Technology, and Sony, as well as by major manufacturers of devices incorporating NAND flash chips. Pinout is a term used in Electronics to describe how an Electrical connector is wired Thin small-outline packages, or TSOP s are a type of Surface mount IC package The land grid array ( LGA) is a type of Surface-mount packaging used for Integrated circuits It can be electrically connected A ball grid array ( BGA) is a type of Surface-mount packaging used for Integrated circuits BGA The BGA is descended from the Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside Serial Presence Detect ( SPD) refers to a standardized way to automatically access information about a computer memory module. SDRAM refers to synchronous Dynamic random access memory, a term that is used to describe dynamic random access memory that has a synchronous interface Micron Technology ("Micron" is a multinational company based in Boise, Idaho, USA best known for producing many forms of Semiconductor is a multinational conglomerate corporation headquartered in Minato Tokyo, Japan, and one of the world's largest Media conglomerates with ^[5]

A group of vendors, including Intel, Dell, and Microsoft formed a Non-Volatile Memory Host Controller Interface (NVMHCI) Working Group. The multinational technology company Dell Inc develops manufactures sells and supports Personal computers and other computer-related products Microsoft Corporation is an American multinational Computer technology Corporation, which rose to dominate the Home computer ^[6] 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. Not to be confused with PCI-X, a different bus architecture Peripheral Component Interconnect Express, officially abbreviated as PCI-E

Distinction between NOR and NAND flash

NOR and NAND flash differ in two important ways:

• the connections of the individual memory cells are different
• the interface provided for reading and writing the memory is different (NOR allows random-access for reading, NAND allows only page access)

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. Magnetic storage and magnetic recording are terms from Engineering referring to the storage of Data on a Magnetized medium A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device

NOR and NAND flash get their names from the structure of the interconnections between memory cells. ^[7] In NOR flash, cells are connected in parallel to the bit lines, allowing cells to be read and programmed individually. In Semiconductor terminology the bitline (BL is where a single storage site (Bit is accessed when intersected with a word line (WL 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. Definition The NAND operation is a Logical operation on two Logical values typically the values of two Propositions that produces a value

When NOR flash was developed, it was envisioned as a more economical and conveniently rewritable ROM than contemporary EPROM, EAROM, and EEPROM memories. An EPROM, or E rasable P rogrammable '''''R'''ead-'''O'''nly '''M'''emory'', is a type of memory chip that retains its EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable 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, a large grid of NAND flash memory cells will occupy only a small fraction of the area of equivalent NOR cells (assuming the same CMOS process resolution, e. Complementary metal–oxide–semiconductor ( CMOS) (pronounced "see-moss" siːmɔːs ˈsiːmɒs is a major class of Integrated circuits CMOS technology g. 130 nm, 90 nm, 65 nm). A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a 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. A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device

Endurance

The endurance of NAND flash is much greater than that of NOR flash (typically 1,000,000 cycles vs. 100,000 cycles). This is because programming and erasure in NOR flash rely on different submicroscopic processes (hot electron injection), while they are perfectly symmetric in NAND flash (Fowler-Nordheim tunneling). Hot carrier injection is the phenomenon in solid state devices or Semiconductors where either an Electron or a "hole" gains sufficient Field emission (FE is the emission of electrons from the surface of a condensed phase into another phase due to the presence of high electric fields ^[7] The asymmetric nature of NOR flash programming and erasure increases the rate at which memory cells degrade, over many program/erase cycles.

The superior symmetric programming method of NAND flash has in fact been adopted in many NOR flash designs, so that some modern NOR chips boast endurance comparable to NAND flash. ^[7]

Serial flash

Serial flash is a small, low-power flash memory that uses a serial interface, typically SPI, for sequential data access. Interface The SPI bus specifies four logic signals SCLK &mdash Serial Clock (output from master MOSI/SIMO &mdash Master Output Slave Input (output 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. An embedded system is a special-purpose Computer system designed to perform one or a few dedicated functions often with Real-time computing constraints A printed circuit board, or PCB, is used to mechanically support and electrically connect Electronic components using conductive pathways or traces This may permit a reduction in board space, power consumption, and total system cost.

There are several reasons why a serial device, with fewer external pins than a parallel device, can significantly reduce overall cost:

• Many ASICs are pad-limited, meaning that the size of the die is constrained by the number of wire bond pads, rather than the complexity and number of gates used for the device logic. A die in the context of Integrated circuits is a small block of semiconducting material on which a given functional circuit is fabricated Wire bonding is a method of making interconnections between a microchip and other electronics as part of semiconductor device fabrication. Eliminating bond pads thus permits a more compact integrated circuit, on a smaller die; this increases the number of dies that may be fabricated on a wafer, and thus reduces the cost per die. A wafer is a thin slice of Semiconductor material such as a Silicon crystal used in the fabrication of Integrated circuit and other microdevices
• Reducing the number of external pins also reduces assembly and packaging costs. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside A serial device may be packaged in a smaller and simpler package than a parallel device.
• Smaller and lower pin-count packages occupy reduced PCB area.
• Lower pin-count devices simplify PCB routing.

Firmware storage

With the increasing speed of modern CPUs, parallel flash devices are often too slow to execute in place program code stored on them. In Computer science, execute in place (XIP is a method of executing programs directly from long term storage rather than copying it into RAM. Conversely, modern SRAM offers access times below 10 ns, while DDR2 SDRAM offers access times below 20 ns. Static random access memory (SRAM is a type of Semiconductor memory where the word static indicates that unlike ''dynamic'' RAM (DRAM, it does not A nanosecond ( ns) is one billionth of a second See also times of other orders of magnitude. SDRAM refers to synchronous Dynamic random access memory, a term that is used to describe dynamic random access memory that has a synchronous interface Because of this, it is often necessary to shadow code stored in flash into RAM; that is, code must be 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. In Computing, firmware is a computer program that is Embedded in a hardware device for example a Microcontroller. ^[8] 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. A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device Ethernet is a family of frame -based Computer networking technologies for Local area networks (LANs ADSL modem or DSL modem is a device used to connect a single Computer or Router to a DSL phone line in order to use an ADSL A wireless network interface controller (WNIC is a Network card which connects to a Radio -based Computer network, unlike a regular network interface

Flash file systems

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 file systems which spread writes over the media and deal with the long erase times of NOR flash blocks. Wear levelling (also written wear leveling) is a technique for prolonging the Service life of some kinds of erasable Computer storage media such as In Mathematics, Computer science, Telecommunication, and Information theory, error detection and correction has great practical importance in In Computing, a file system (often also written as filesystem) is a method for storing and organizing Computer files and the data they contain to make 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.

One of the earliest flash file systems was Microsoft's FFS2 (presumably preceded by FFS1), for use with MS-DOS in the early 1990s. Microsoft Corporation is an American multinational Computer technology Corporation, which rose to dominate the Home computer MS-DOS (short for M icro' s' oft D isk O perating S ystem is an Operating system commercialized by Microsoft. ^[9]

Around 1994, the PCMCIA, an industry group, approved the Flash Translation Layer (FTL) specification, which allowed a Linear Flash device to look like a FAT disk, but still have effective wear levelling. Linear Flash is a PC card Flash memory format now used primarily in Cisco Routers Linear Flash requires no battery support unlike somewhat faster Templateinfobox filesystem whilst covering all 3 file systems please make any style changes to both at the same time Wear levelling (also written wear leveling) is a technique for prolonging the Service life of some kinds of erasable Computer storage media such as Other commercial systems such as FlashFX and FlashFX Pro by Datalight were created to avoid patent concerns with FTL.

ZFS by Sun Microsystems has been optimized to manage Flash SSD systems, both as cache as well as main storage facilities, available for OpenSolaris, Mac OSX, and the Linux operating system. In Computing, ZFS is a File system designed by Sun Microsystems for the Solaris Operating System. Sun Microsystems Inc ( is a multinational vendor of Computers computer components Computer software, and Information technology services OpenSolaris is an Open source project created by Sun Microsystems to build a developer community around Solaris Operating System technology Mac OS X (mæk oʊ ɛs tɛn is a line of computer Operating systems developed marketed and sold by Apple Inc, the latest of which is pre-loaded on all currently Linux (commonly pronounced ˈlɪnəks Sun has announced a complete line of Flash enabled systems and storage devices.

JFFS was the first flash-specific file system for Linux, but it was quickly superseded by JFFS2, originally developed for NOR flash. The Journalling Flash File System (or JFFS) is a Log-structured file system for use on NOR Flash memory devices on the Linux operating system Linux (commonly pronounced ˈlɪnəks Journalling Flash File System version 2 or JFFS2 is a Log-structured file system for use in Flash memory devices Then YAFFS was released in 2002, dealing specifically with NAND flash, and JFFS2 was updated to support NAND flash too. YAFFS ( Yet Another Flash File System) was designed and written by Charles Manning, of Whitecliffs, New Zealand for the company Aleph One

In practice, flash file systems are only used for "Memory Technology Devices" ("MTD"), which are embedded flash memories that do not have a controller. A Memory Technology Device (MTD is a type of embedded Flash memory that Consists of eraseblocks rather than sectors like in Hard drives. 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. A memory card or flash memory card is a solid-state electronic Flash memory Data storage device used with Digital Wear levelling (also written wear leveling) is a technique for prolonging the Service life of some kinds of erasable Computer storage media such as In Mathematics, Computer science, Telecommunication, and Information theory, error detection and correction has great practical importance in 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. Templateinfobox filesystem whilst covering all 3 file systems please make any style changes to both at the same time

Capacity

Multiple chips are often arrayed to achieve higher capacities for use in consumer electronic devices such as multimedia player or GPS. Media Player was a media player originally included in Windows 3 Basic concept of GPS operation A GPS receiver calculates its position by carefully timing the signals sent by the constellation of GPS Satellites high above the Earth The capacity of flash chips generally follows Moore's Law because they are manufactured with many of the same integrated circuits techniques and equipment. Moore's law describes an important trend in the History of computer hardware. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside

Consumer flash drives typically have sizes measured in powers of two (e. g. 512 MB, 8 GB), but unlike DIMMs (and like hard drives) these sizes use decimal units. A megabyte is a unit of Information or Computer storage equal to either 106 (1000000 Bytes or 220 (1048576 bytes depending on A DIMM, or dual in-line memory module, comprises a series of Dynamic random access memory Integrated circuits These modules are mounted on a Printed A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol to form a Decimal multiple or

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. ( is a multinational conglomerate manufacturing company headquartered in Tokyo, Japan. SanDisk Corporation ( is an American Multinational corporation which designs and markets Flash memory card products Definition The NAND operation is a Logical operation on two Logical values typically the values of two Propositions that produces a value A gigabyte (derived from the SI prefix Giga-) is a unit of Information or Computer In Electronics, a multi-level cell (MLC is a memory element capable of storing more than a single bit of information In September 2005, Samsung Electronics announced that it had developed the world’s first 2 GB chip. Samsung Electronics (SEC Hangul:삼성전자,,,) is the world's largest Consumer electronics company headquartered in Seocho Samsung Town in ^[10]

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. Complementary metal–oxide–semiconductor ( CMOS) (pronounced "see-moss" siːmɔːs ˈsiːmɒs is a major class of Integrated circuits CMOS technology ^[11]

In January 2008 Sandisk announced availability of their 12GB MicroSDHC and 32GB SDHC Plus cards. SanDisk Corporation ( is an American Multinational corporation which designs and markets Flash memory card products ^[12][13]

Transfer rates

Commonly advertised is the maximum read speed, NAND flash memory cards are generally faster at reading than writing.

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.

Sometimes denoted in MB/s (megabyte per second), or in number of "X" like 60x 100x or 150x. "X" speed rating makes reference to the speed at which a legacy audio CD drive would deliver data, 1x is equal to 150 kibibytes per second. A kibibyte (a contraction of ki lo bi nary byte) is a unit of Information or Computer storage, established by the International

For example, a 100x memory card goes to 150 KiB x 100 = 15000 KiB per second = 14. 65 MiB per second.

Note that the exact speed depends on whether the marketer means 10^6 bytes or 2^20 bytes by "megabyte". A megabyte is a unit of Information or Computer storage equal to either 106 (1000000 Bytes or 220 (1048576 bytes depending on

Flash memory as a replacement for hard drives

Main article: Solid-state drive

An obvious extension of flash memory would be as a replacement for hard disks. A solid-state drive ( SSD) is a Data storage device that uses solid-state memory to store persistent Data. A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device 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. A solid-state drive ( SSD) is a Data storage device that uses solid-state memory to store persistent Data.

There remain some aspects of flash-based SSDs that make the idea unattractive. Most importantly, 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. ^[14][15]

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. Events 1218 - The Fifth Crusade leaves Acre for Egypt. 1276 - Magnus Ladulås is crowned Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. South Korea, officially the Republic of Korea and often referred to as Korea ( Korean: 대한민국 tɛː Samsung Electronics (SEC Hangul:삼성전자,,,) is the world's largest Consumer electronics company headquartered in Seocho Samsung Town in ^[16] 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. The Las Vegas metropolitan area includes the Las Vegas Valley a 600-square-mile (1600 km² basin and surrounding areas that is part of Clark County in southern The International Consumer Electronics Show (CES is a Trade show held each January in Las Vegas, Nevada, and is sponsored Taiwan ( Taiwanese: Tâi-oân/Tāi-oân (historically 大灣/台員/大員/台圓/大圓/台窩灣 is an Island in East Asia. A-DATA Technology ( ( TSEC3260 is a Taiwanese memory manufacturer founded on May 2001 by Chairman and CEO Mr A solid-state drive ( SSD) is a Data storage device that uses solid-state memory to store persistent Data. ^[17] Sandisk announced an OEM 32 GB 1. 8" SSD drive at CES 2007. ^[18] The XO-1, developed by the One Laptop Per Child (OLPC) association, uses flash memory rather than a hard drive. The XO-1, previously known as the $100 Laptop or Children's Machine, is an inexpensive Laptop computer intended to be distributed to children in developing 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. ^[19]

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. A hybrid drive or Hybrid Hard Drive (HHD is a type of large-buffer computer hard disk drive. ReadyBoost is an operating system feature included with Microsoft 's Windows Vista Operating system. In Computer science, a cache (kæʃ like "cash") is a collection of data duplicating original In Computing, an executable (file causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a file that only contains Also, Addonics has a PCI adapter for 4 CF cards,^[20] 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 2GB to 20GB, depending on model. The ASUS Eee PC (pronounced as the letter e, IPA /iː/ is a Subnotebook / Netbook computer designed by ASUS. The Apple Inc. Macbook Air has the option to upgrade the standard hard drive to a 64GB Solid State hard drive. Apple Inc, ( formerly Apple Computer Inc, is an American Multinational corporation with a focus on designing and manufacturing Consumer electronics The MacBook Air is a thin lightweight Macintosh Notebook computer designed by Apple. The Lenovo ThinkPad X300 also features a built-in 64GB Solid State Drive. Lenovo Group Limited (,) is China's largest and the world's fourth largest Personal computer manufacturer after Hewlett-Packard and Dell of the U ThinkPad is a brand of portable Laptop and Notebook Personal computers originally designed manufactured and sold by IBM.

NAND Flash scalability

The aggressive trend of process design rule shrinks in NAND Flash memory technology effectively accelerates Moore's Law.

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 ~20 nm by ~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. Moore's law describes an important trend in the History of computer hardware.

As the feature size of a Flash memory cell reaches the minimum limit (currently estimated ~20 nm), it is likely Flash capacity will be extended by MLC operation or extended 3D stacking.

See also

• List of emerging technologies
• CompactFlash
• Wear levelling
• DataFlash
• Open NAND Flash Interface Working Group
• 1T-FLASH
• List of flash file systems

References

• Digital Memories Survive Extremes
• Flash memory database

Flash file systems (general references)

• Presentation on various Flash File Systems - 9/24/2007
• Article regarding various Flash File Systems - 2005 USENIX Annual Conference
• Survey of various Flash File Systems - 8/10/2005

External links

• Open NAND Flash Interface Working Group
• NAND vs. NOR flash technology: The designer should weigh the options when using flash memory
• A Nonvolatile Memory Overview
• How Flash Memory Works
• SanDisk Flash Memory Plant
• What is NAND Flash
• NAND Flash Applications
• NAND Flash Applications Design Guide from Toshiba (explains the low-level details of interfacing with common NAND flash chips)
• NAND vs. NOR Flash Memory from Toshiba
• Samsung Develops New Flash Memory Chip - AP, October 23, 2007
• Numonyx - Intel & ST Micro Flash merger