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Encyclopedia > Flash memory
Computer memory types
Volatile
Non-Volatile
A USB flash drive. The chip on the left is the flash memory. The microcontroller is on the right.
A USB flash drive. The chip on the left is the flash memory. The microcontroller is on the right.

Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed. It is a technology that is primarily used in memory cards, USB flash drives (thumb drives, handy drive, memory stick, flash stick, jump drive), which are used for general storage and transfer of data between computers and other digital products. It is a specific type of EEPROM 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. Examples of applications include PDAs and laptop computers, digital audio players, digital cameras and mobile phones. It has also gained some popularity in the game console market, where it is often used instead of EEPROMs or battery-powered static RAM (SRAM) for game save data. The terms storage (U.K.) or memory (U.S.) refer to the parts of a digital computer that retain physical state (data) for some interval of time, possibly even after electrical power to the computer is turned off. ... Volatile memory refers to computer memory that must be powered to maintain its data. ... Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit. ... eDRAM stands for embedded DRAM, a capacitor-based dynamic random access memory usually integrated on the same die or in the same package as the main ASIC or processor, as opposed to external DRAM modules and transistor-based SRAM typically used for caches. ... Static random access memory (SRAM) is a type of semiconductor memory. ... 1T-SRAM is MoSyss implementation of embedded-DRAM on a conventional digital-logic (standard-cell) ASIC process. ... Z-RAM, short for zero capacitor DRAM is a new type of computer memory in development by Innovative Silicon Inc. ... TTRAM, short for Twin Transistor RAM is new type of computer memory in development by Renesas. ... The Williams tube or (more accurately) the Williams-Kilburn tube (after Freddie Williams and coworker Tom Kilburn), developed about 1946 or 1947, was a cathode ray tube used to store electronic data. ... Mercury memory of UNIVAC I (1951) Delay line memory was a form of computer memory used on some of the earliest digital computers, such as the EDSAC and UNIVAC I. The basic concept of the delay line originated with World War II radar research, specifically to reduce clutter from reflections... The Selectron was an early form of computer memory developed by RCA. Development started in 1946 with a planned production of 200 by the end of the year, but production problems meant that they were still not available by the middle of 1948. ... It has been suggested that this article or section be merged with NVRAM. (Discuss) Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is computer memory that can retain the stored information even when not powered. ... Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ... D23128C PROM on the board of ZX Spectrum A programmable read-only memory (PROM) or field programmable read-only memory (FPROM) is a form of digital memory where the setting of each byte is locked by a fuse or antifuse. ... Read-only memory (ROM) is used as a storage medium in computers. ... EPROM. The small quartz window admits UV light during erasure. ... An EEPROM (also called an E2PROM)[] or Electronically Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices to store small amounts of volatile (configuration) data. ... Ferroelectric RAM (FRAM or FeRAM) is a type of non-volatile computer memory, similar to EEPROM but based on electric field orientation and with near-unlimited number (exceeding 1010 for 5V devices and even more for 3. ... Magnetoresistive Random Access Memory (MRAM) is a non-volatile computer memory (NVRAM) technology, which has been in development since the 1990s. ... Phase-change memory (also known as PCM, PRAM, Ovonic Unified Memory and Chalcogenide RAM [C-RAM]) is a type of non-volatile computer memory. ... Wikipedia does not have an article with this exact name. ... RRAM or Resistive Random Access Memory is a new non-volatile memory type begin developed by Sharp, Samsung, Fujitsu, Spansion, Macronix, Winbond and other companies. ... Nano-RAM, is a proprietary computer memory technology from the company Nantero. ... hi i am cool xbox is all most as cool as me hi again ... A 16×16 cm area core memory plane of 128×128 bits, i. ... Bubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles, which each store one bit of data. ... Download high resolution version (2592x1944, 982 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (2592x1944, 982 KB) Wikipedia does not have an article with this exact name. ... A USB flash drive, shown with a 24 mm U.S. quarter coin for scale. ... It has been suggested that this article or section be merged with embedded microprocessor. ... It has been suggested that this article or section be merged with NVRAM. (Discuss) Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is computer memory that can retain the stored information even when not powered. ... This article or section does not cite any references or sources. ... This article does not cite any references or sources. ... A USB flash drive, shown with a 24 mm U.S. quarter coin for scale. ... An EEPROM (also called an E2PROM)[] or Electronically Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices to store small amounts of volatile (configuration) data. ... User with PDA Personal digital assistants (PDAs) are handheld computers that were originally designed as personal organizers, but became much more versatile over the years. ... Apple iPod, the most popular hard drive-based digital audio player An embedded hard drive-based player (Creative Zen Vision:M), one of the many alternatives for the iPod An MP3 CD player (Philips Expanium) Some mobile phones can be used as digital audio players, such as the Nokia 6233. ... This article or section does not cite any references or sources. ... Static Random Access Memory (SRAM) is a type of semiconductor memory. ...

Contents

Overview

Flash memory is non-volatile, which means that it does not need power 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 for applications such as storage on battery-powered 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 immersion in water. It has been suggested that this article or section be merged with NVRAM. (Discuss) Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is computer memory that can retain the stored information even when not powered. ... In telecommunication, the term access time has the following meanings: In a telecommunication system, the elapsed time between the start of an access attempt and successful access. ... Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit. ... Typical hard drives of the mid-1990s. ...


Although technically a type of EEPROM, the term "EEPROM" is generally used to refer specifically to non-flash EEPROM which is eraseable in small blocks, typically bytes. Because an erase cycle is slow, the large size of a flash ROM's erase block can make programming it faster than old-style EEPROM.


Principles of operation

Flash memory stores information in an array of floating-gate transistors, called "cells". 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. It has been suggested that this article or section be merged into Floating_Gate_MOSFET. (Discuss) A cross-section of a floating-gate transistor The floating-gate transistor is a kind of transistor that is commonly used for non-volatile storage such as flash, EPROM and EEPROM memory. ...

A flash memory cell.
A flash memory cell.

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NOR flash

Programming a NOR memory cell (setting it to logical 0), via hot-electron injection.
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.
Erasing a NOR memory cell (setting it to logical 1), via quantum tunneling.

. During read-out, a voltage is applied to the CG, and the MOSFET channel will become conducting or remain insulating, depending on the VT of the cell, which is in turn controlled by charge on the FG. The presence or absence of current flow through the MOSFET channel is sensed and forms a binary code, reproducing the stored data. 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. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... It has been suggested that this article or section be merged into Binary. ... For other uses, see Data (disambiguation). ... This article is about the unit of information. ...


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 between the source and the drain
  • 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. 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, that is 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. This article or section is in need of attention from an expert on the subject. ... Quantum tunneling is the quantum-mechanical effect of transitioning through a classically-forbidden energy state. ...


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 on-chip via 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.
NOR flash memory wiring and structure on silicon.

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NAND flash

NAND gate flash uses tunnel injection for writing and tunnel release for erasing. NAND flash memory forms the core of the removable USB interface storage devices known as USB flash drives, as well as most memory card formats available today. NAND Logic gate The Sheffer stroke, written | or ↑, denotes a logical operation that is equivalent to the negation of the conjunction operation, expressed in ordinary language as not both. It is also called the alternative denial, since it says in effect that at least one of its operands is false. ... Tunnel injection is the effect used to program NAND flash memory. ... Tunnel injection is the quantum tunneling effect, also called Fowler-Nordheim tunnel injection, when charge carriers are injected to an electric conductor through a thin layer of an electric insulator. ... A USB Series “A” plug, the most common USB plug Universal Serial Bus (USB) is a serial bus standard to interface devices. ... A USB flash drive, shown with a 24 mm U.S. quarter coin for scale. ... This article does not cite any references or sources. ...

NAND flash memory wiring and structure on silicon.

Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ...

New designs

As manufacturers increase the density of data storage in flash devices, individual memory cells are shrinking and the number of electrons stored in any cell is becoming very small. Coupling between adjacent floating gates can change the write characteristics of cells, making it increasingly difficult to design flash devices for high data integrity. New designs, such as charge trap flash, attempt to provide better isolation between adjacent cells. Charge Trap Flash (Often abbreviated to CTF) is a new technology to fabricate a NAND flash device invented by Samsung Electronics in 2006. ...


History

Flash memory (both NOR and NAND types) was invented by Dr. Fujio Masuoka while working for Toshiba in 1984. 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. Toshiba Corporations headquarters (Center) in Hamamatsucho, Tokyo Toshiba Corporation sales by division for year ending March, 31 2005 Toshiba Corporation ) (TYO: 6502 ) is a multinational high technology electrical and electronics manufacturing firm, headquartered in Tokyo, Japan. ... Running water frozen by flash. ... The Institute of Electrical and Electronics Engineers or IEEE (pronounced as eye-triple-ee) is an international non-profit, professional organization incorporated in the State of New York, United States. ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ...


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. [citation needed] 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. In computer science, random access is the ability to access a random element of a group in equal time. ... Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ... This article does not cite any references or sources. ... In computing, firmware is software that is embedded in a hardware device. ... The term set-top box (STB) describes a device that connects to a television and some external source of signal, and turns the signal into content then displayed on the screen. ... A 64 MB CompactFlash Type I card A 32 MB High Speed CompactFlash Type I card CompactFlash (CF) was originally developed as a type of data storage device used in portable electronic devices. ...


Toshiba announced NAND flash at ISSCC in 1989. 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 makes NAND flash unsuitable to replace program ROM, since most microprocessors and microcontrollers cannot directly execute programs stored in memory without random access; however, 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; the microSD card has an area of just over 1.5 cm², with a thickness of less than 1 mm. Toshiba Corporations headquarters (Center) in Hamamatsucho, Tokyo Toshiba Corporation sales by division for year ending March, 31 2005 Toshiba Corporation ) (TYO: 6502 ) is a multinational high technology electrical and electronics manufacturing firm, 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. ... In computer storage, secondary storage, or external memory, is computer memory that is not directly accessible to the central processing unit of a computer, requiring the use of computers input/output channels. ... Typical hard drives of the mid-1990s. ... In computing, sound reproduction, and video, an optical disc is flat, circular, usually polycarbonate disc whereon data is stored. ... This article does not cite any references or sources. ... A 128MB SmartMedia flash memory card. ... A 32 MB MultiMediaCard MultiMediaCard A 128 MB RS-MMC card and an adapter An RS-MMC card with adapter attached The MultiMediaCard (MMC) is a flash memory memory card standard. ... 16Mb SD Card Secure Digital, or SD, is a flash memory data storage device based on Toshibas earlier Multi Media Cards (MMC). ... A 2GB Sony High Speed Memory Stick PRO Duo with MagicGate support. ... xD-Picture Card (front) xD-Picture Card (back) The xD-Picture Card is a type of flash memory memory card, used mainly in digital cameras. ... Categories: Computer stubs | Solid-state computer storage media ... Announced for the first time by SanDisk Corporation at CeBIT 2003, the miniSD joined the MemoryStick Duo and xD-Picture Card at this small Form factor. ... The width of two microSD cards together is less than that of this 24 mm diameter coin. ... A pqi Intelligent Stick Pro 170 memory card Intelligent Stick is a USB-based flash memory card which was developed by the pqi company in 2002. ...


Limitations

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. Although data structures in flash memory can not 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. A nibble (or less commonly but more accurately, nybble) is the computing term for a four-bit aggregation, or half an octet (an octet being an 8-bit byte). ...


Another limitation is that flash memory has a finite number of erase-write cycles (most commercially available flash products are guaranteed to withstand 1000 write-erase-cycles for block 0, and no guarantees for other blocks[citation needed]). 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. Another mechanism is to perform write verification and remapping to spare sectors in case of write failure, which is named bad block management (BBM). With these mechanisms in place, some industry analysts[1] have calculated that flash memory can be written to at full speed continuously for 51 years before exceeding its write endurance, even if such writes frequently cause the entire disk to be overwritten. This figure (51 years) involved a worst-case scenario using specific data parameters and should not be confused with a particular "shelf life" for a flash memory device. The bottom line is that a typical user using a commercial device, such as a camera, with a flash drive will probably not wear out the memory for the effective life of the camera. However, it - like any other hardware component - can fail. Anyone using flash memory (and any other medium) for critical data would be well advised to backup the data to another device (preferably of a different medium). Many have found it very fast and reliable for 'read-only' operating systems such as thin clients and routers. Wear levelling (also written -levelling) is a technique for prolonging the service life of some kinds of eraseable computer storage media, e. ... A Thin client is a computer (client) in client-server architecture networks which has little or no application logic, so it has to depend primarily on the central server for processing activities. ... This article describes the computer networking device. ...


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. Dram can mean several things: Dram (unit), an imperial unit of volume Dram, an imperial unit of weight or mass, see avoirdupois and apothecaries system Ottoman dram, a unit of weight, see dirhem Armenian dram, a monetary unit DRAM, a type of RAM Category: ... Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ... An EEPROM (also called an E2PROM)[] or Electronically Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices to store small amounts of volatile (configuration) data. ... In computer science, random access is the ability to access a random element of a group in equal time. ... An address bus is (part of) a computer bus, used by CPUs or DMA-capable units for communicating the physical addresses of computer memory elements/locations that the requesting unit wants to access (read/write). ...


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. 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 computer science, an execute in place filesystem is one that allows certain sections of programs to be stored read-only in an area other than main system memory. ... Windows XP loading drivers during a Safe Mode bootup A device driver, or a software driver is a specific type of computer software, typically developed to allow interaction with hardware devices. ...


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 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. NAND flash memories cannot provide execute in place due to their different construction principles. These memories are accessed much like block devices such as hard disks or memory cards. The pages are typically 512 or 2,048 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. Toshiba Corporations headquarters (Center) in Hamamatsucho, Tokyo Toshiba Corporation sales by division for year ending March, 31 2005 Toshiba Corporation ) (TYO: 6502 ) is a multinational high technology electrical and electronics manufacturing firm, headquartered in Tokyo, Japan. ... In computing (specifically data transmission and data storage), block size indicates a nominal size, usually expressed in bytes or bits, of a block of data. ... Typical hard drives of the mid-1990s. ... This article does not cite any references or sources. ... It has been suggested that Error-correcting code be merged into this article or section. ... 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) or time (storage). ...


The pages are typically arranged in blocks. A typical block would be 32 pages of 512 bytes or 64 pages of 2,048 bytes.


While programming is performed on a page basis, erasure can only be performed on a block basis.


NAND devices also require bad block management to be performed by 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, and a number of blocks on the flash chip are set aside for storing mapping tables to deal with bad blocks.


The error-correcting and detecting checksum will typically correct an error where one bit per 256 bytes is incorrect. 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 in the memory is corrupted, the contents are partly lost, i.e. it is no longer possible to reconstruct the original contents.


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 manfacturers achieve far higher yields than would be possible if all blocks were tested good. This significantly reduces NAND flash costs and only slightly increases the size 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. A Master Boot Record (MBR), or partition sector, is the 512-byte boot sector that is the first sector (Sector 0) of a partitioned data storage device such as a hard disk. ...


When executing software from NAND memories, virtual memory strategies are used: memory contents must first be paged or copied into memory-mapped RAM and executed there. 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 random access storage area. 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. How virtual memory maps to physical memory Virtual memory is an addressing scheme implemented in hardware and software that allows non-contiguous memory to be addressed as if it were contiguous. ... In computer operating systems, paging memory allocation, paging refers to the process of managing program access to virtual memory pages that do not currently reside in RAM. It is implemented as a task that resides in the kernel of the operating system and gains control when a page fault takes... This 68451 MMU could be used with the Motorola 68010 MMU, short for memory management unit or sometimes called paged memory management unit as PMMU, is a class of computer hardware components responsible for handling memory accesses requested by the CPU. Among the functions of such devices are the translation... Overlays are a programming method that allow computer programs to be bigger than the amount of virtual address space available to the user. ... Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ... It has been suggested that Crash counting be merged into this article or section. ...


Standardization

A group called the Open NAND Flash Interface Working Group (ONFI) has developed a standardized low-level interface for NAND flash chips. This allows interoperability between conforming NAND devices from different vendors. The ONFI specification version 1.0[2] was released on December 28, 2006. It specifies: The Open NAND Flash Interface Working Group, or ONFI, is a consortium of technology companies working to develop open standards for NAND flash memory chips and devices that communicate with them. ...

  • 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.[3] Pinout is a term used in electronics to describe how an electrical connector is wired. ... This article does not cite any references or sources. ... The land grid array (LGA) is a physical interface for microprocessors of the Intel Pentium 4 family. ... For the Bulgarian Go Association, see Bulgarian Go Association. ... Integrated circuit showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... Serial Presence Detect (SPD) refers to a standardized way to access manufacturer information from a computer memory module. ... This article or section does not cite any references or sources. ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... Micron Technology (Micron) NYSE: MU is a multinational company based in Boise, Idaho, USA, best known for producing many forms of semiconductor devices. ... Sony Corporation ) is a Japanese multinational corporation and one of the worlds largest media conglomerates with revenue of $66. ...


A group of vendors, including Intel, Dell, and Microsoft formed a Non-Volatile Memory Host Controller Interface (NVMHCI) Working Group [4]. 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. Dell Inc. ... Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... PCI Express (formerly known as 3GIO for 3rd Generation I/O, not to be mistaken with PCI-X) is an implementation of the PCI computer bus that uses existing PCI programming concepts and communications standards, but bases it on a much faster serial communications system. ...


Understanding the 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 block 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 is a term from engineering referring to the storage of data on a magnetised medium. ... Typical hard drives of the mid-1990s. ...


NOR and NAND flash get their names from the structure of the interconnections between memory cells.[5] 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. This article or section does not cite any references or sources. ... This article is about logical nor Nór. ... ...


When NOR flash was developed, it was envisioned as a more economical and conveniently rewriteable 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. EPROM. The small quartz window admits UV light during erasure. ... Read-only memory (ROM) is used as a storage medium in computers. ... An EEPROM (also called an E2PROM)[] or Electronically Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices to store small amounts of volatile (configuration) data. ...


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.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. Static CMOS Inverter Complementary metal–oxide–semiconductor (CMOS) (see-moss, IPA: ), is a major class of integrated circuits. ... Typical hard drives of the mid-1990s. ...


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 microscopic processes (hot electron injection and quantum tunneling, respectively), while they are perfectly symmetric in NAND flash (Fowler-Nordheim tunneling).[5] The asymmetric nature of NOR flash programming and erasure increases the rate at which memory cells degrade, over many program/erase cycles. This article or section does not cite any references or sources. ... Quantum tunneling is the quantum-mechanical effect of transitioning through a classically-forbidden energy state. ... Quantum tunneling is the quantum-mechanical effect of transitioning through a classically-forbidden energy state. ...


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.[5]


Serial flash

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. The Serial Peripheral Interface Bus or SPI (often pronounced es-pē-ī or spy) bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. ... A router, an example of an embedded system. ... Part of a 1983 Sinclair ZX Spectrum computer board. ...


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. 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.
  • Reducing the number of external pins also reduces assembly and packaging costs. 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.

This article does not cite any references or sources. ... A die in the context of integrated circuits is a small piece of semiconducting material on which a given circuit is fabricated. ... Gold wire ball-bonded to a gold contact pad Aluminium wires wedge-bonded to a KSY34 transistor die The interconnection in a power package are made using thick aluminium wires (250 to 400 µm) wedge-bonded Wire bonding is a method of making interconnections between a microchip and the outside... It has been suggested that Wafer prober be merged into this article or section. ... Integrated circuit showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... Routing is a crucial step in the design of integrated circuits. ...

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. Conversely, modern SRAM offers access times below 10 ns, while DDR2 SDRAM offers access times below 20 ns. 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. [6] 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. In computer science, an execute in place filesystem is one that allows certain sections of programs to be stored read-only in an area other than main system memory. ... Static Random Access Memory (SRAM) is a type of semiconductor memory. ... To help compare orders of magnitude of different times this page lists times between 10−9 seconds and 10−8 seconds (1 nanosecond and 10 nanoseconds) See also times of other orders of magnitude. ... This article or section does not cite any references or sources. ... To help compare orders of magnitude of different times this page lists times between 10−9 seconds and 10−8 seconds (1 nanosecond and 10 nanoseconds) See also times of other orders of magnitude. ... Look up RAM and random access memory in Wiktionary, the free dictionary Different types of RAM. From top to bottom: DIP, SIPP, SIMM 30 pin, SIMM 72 pin, DIMM, DDR DIMM Random access memory (sometimes random-access memory), commonly known by its acronym RAM, is a type of computer storage... In computing, firmware is software that is embedded in a hardware device. ... Typical hard drives of the mid-1990s. ... Ethernet is a large, diverse family of frame-based computer networking technologies that operates at many speeds for local area networks (LANs). ... An ADSL modem, also known as a DSL modem, is a device used to connect one or more computers to a phone line, in order to use an ADSL service. ... A wireless network interface card (WNIC) is a network card which connects to a radio-based computer network, unlike a regular network card (NIC) which connects to a wire-based network such as token ring or ethernet. ...


Flash file systems

Because of the particular characteristics of flash memory, it is best used with specifically designed 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. One of the earliest flash file systems was Microsoft's FFS2 (presumably preceded by FFS1), for use with MS-DOS in the early 1990s. Around 1994, the PCMCIA industry group approved the FTL (Flash Translation Layer) specification, which allowed a Linear Flash device to look like a FAT disk, but still have effective wear levelling. Other commercial systems such as FlashFX by Datalight were created to avoid patent concerns with FTL. It has been suggested that Crash counting be merged into this article or section. ... Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ... Linear Flash is a PC card flash memory format now used primarily in Cisco routers. ... File Allocation Table (FAT) is a partially patented file system developed by Microsoft for MS-DOS and was the primary file system for consumer versions of Microsoft Windows up to and including Windows Me. ... Wear levelling (also written -levelling) is a technique for prolonging the service life of some kinds of eraseable computer storage media, e. ...


JFFS was the first flash-specific file system for Linux, but it was quickly superseded by JFFS2, originally developed for NOR flash. Then YAFFS was released in 2003, dealing specifically with NAND flash, and JFFS2 was updated to support NAND flash too. In practice, these filesystems are only used for "Memory Technology Devices" ("MTD"), which are embedded flash memories which do not have a controller. Removable flash media, such as SD and CF cards and USB flash drives, have a controller (often built into the card) to perform wear-levelling and error correction, so use of JFFS2 or YAFFS does not add any benefit. These removable flash memory devices are often used with the old FAT filesystem for compatibility with cameras and other portable devices. Controllerless removable flash memory devices also exist; For example, SmartMedia is even electrically compatible with the Toshiba TC58 series of NAND flash chips. The Journaled Flash File System (or JFFS) is a log-structured file system for use on NOR flash memory devices. ... Linux (IPA pronunciation: ) is a Unix-like computer operating system. ... The Journalling Flash File System version 2 or JFFS2 is a log-structured file system for use in flash memory devices. ... This article needs to be cleaned up to conform to a higher standard of quality. ... MTD(Memory Technology Device) is a type of embeded flash memory that: 1. ... A USB flash drive, shown with a 24 mm U.S. quarter coin for scale. ... Wear levelling (also written -levelling) is a technique for prolonging the service life of some kinds of eraseable computer storage media, e. ... In computer science and information theory, error correction consists of using methods to detect and/or correct errors in the transmission or storage of data by the use of some amount of redundant data and (in the case of transmission) the selective retransmission of incorrect segments of the data. ... File Allocation Table (FAT) is a partially patented file system developed by Microsoft for MS-DOS and was the primary file system for consumer versions of Microsoft Windows up to and including Windows Me. ... A 128MB SmartMedia flash memory card. ...


Capacity

Common flash memory parts (individual internal components or "chips") range widely in capacity from kilobits to several gigabits each. Multiple chips are often arrayed to achieve higher capacities for use in devices such as the iPod nano or SanDisk Sansa e200. The capacity of flash chips generally follows Moore's law because they are produced with the same processes used to manufacture other integrated circuits. However, there have also been jumps beyond Moore's law due to innovations in technology. A kilobit is a unit of information storage, abbreviated kbit or sometimes kb. ... A gigabit is a unit of information or computer storage, abbreviated Gbit or sometimes Gb. ... The iPod nano is Apples fourth digital audio player. ... The SanDisk Sansa is a line of flash memory-based digital audio players produced by SanDisk. ... Gordon Moores original graph from 1965 Growth of transistor counts for Intel processors (dots) and Moores Law (upper line=18 months; lower line=24 months) For the observation regarding information retrieval, see Mooers Law. ...


In 2005, Toshiba and SanDisk developed a NAND flash chip capable of storing 1 GB of data using MLC (multi-level cell) 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.[7] Toshiba Corporations headquarters (Center) in Hamamatsucho, Tokyo Toshiba Corporation sales by division for year ending March, 31 2005 Toshiba Corporation ) (TYO: 6502 ) is a multinational high technology electrical and electronics manufacturing firm, headquartered in Tokyo, Japan. ... SanDisk Corporation (NASDAQ: SNDK), formerly SunDisk, is an American multinational corporation which designs and markets flash memory card products. ... ... Samsung Electronics (SEC, Hangul:삼성전자; KSE: 005930, KSE: 005935, LSE: SMSN, LSE: SMSD) is a South Korean Multinational Corporation and one of the worlds largest Electronics and IT companies,[1]. In August 2005, BusinessWeek rated Samsung as the Number 1 consumer electronics brand in the world. ...


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 of 2006, Samsung announced an 8-GB chip produced using a 40-nm manufacturing process.[8] NM may stand for: National Master, a chess title Nautical mile, a unit of length used for maritime and aviation purposes Neal Morse, an American multi-instrumentalist Network marketing, a business model that combines direct marketing with franchising Neurofiber mitosis, a nerve disease, sometimes confused with neurofibromatosis New Mexico, in...


For some flash memory products such as memory cards and USB drives, as of mid 2006, 256-megabyte and smaller devices have been largely discontinued. 1-GB-capacity flash memory has become the normal storage space for people who do not extensively use flash memory, while more and more consumers are adopting 2-GB, 4-GB, or 8-GB flash drives. The highest capacity lays in USB with a current record of 64-GB.[9] ReBoot character, see Megabyte (ReBoot). ...


Hitachi (formerly the OEM hard disk unit supplying IBM) has a competing hard-drive mechanism, the Microdrive, that can fit inside the shell of a type II CompactFlash card. It has a capacity up to 8 GB. BiTMicro offers a 155-GB 3.5-" Solid-State disk, named the "Edisk".[10] Hitachi may refer to: Hitachi (train) trains in Melbourne, Australia. ... IBM redirects here. ... IBM 1 GB Microdrive The Microdrive is a brand name for a miniature, 1-inch hard disk designed to fit in a Compact Flash (CF) Type II slot. ... A 64 MB CompactFlash Type I card A 32 MB High Speed CompactFlash Type I card CompactFlash (CF) was originally developed as a type of data storage device used in portable electronic devices. ...


Speed

Flash memory cards are available in different speeds. Some are specified the approximate transfer rate of the card such as 2 MB per second, 12 MB per second, etc. The exact speed of these cards depends on which definition of "megabyte" the marketer has chosen to use. ReBoot character, see Megabyte (ReBoot). ...


Many cards are simply rated 100x, 130x, 200x, etc. For these cards the base assumption is that 1x is equal to 150 kibibytes per second. This was the speed at which the first CD drives could transfer information, which was adopted as the reference speed for flash memory cards. Thus, when comparing a 100x card to a card capable of 12 MiB per second the following calculations are useful: A kibibyte (a contraction of kilo binary byte) is a unit of information or computer storage, abbreviated KiB (never kiB). 1 kibibyte = 210 bytes = 1,024 bytes The kibibyte is closely related to the kilobyte, which can be used either as an (inaccurate) synonym for kibibyte or to refer to... A mebibyte (a contraction of mega binary byte) is a unit of information or computer storage, abbreviated MiB. 1 MiB = 220 bytes = 1,048,576 bytes = 1,024 kibibytes 1 MiB = 1024 (= 210) kibibytes (KiB), and 1024 MiB equal one gibibyte (GiB). ...


150 KiB x 100 = 15000 KiB per second = 14.65 MiB per second.


Therefore, the 100x card is 14.65 MiB per second, which is faster than the card that is measured at 12 MiB per second.


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. 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 flash SSD in standard 2. ... Typical hard drives of the mid-1990s. ... A flash SSD in standard 2. ...


There remain some aspects of flash-based SSD's 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 SSD's are approaching those of current hard drives.[11][12]


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.[13] Dell Computer introduced the Latitude D430 laptop with 32 GB flash-memory storage in July 2007 -- at a price signficiantly above a hard-drive equipped version. is the 144th day of the year (145th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday (link displays full 2006 calendar) of the Gregorian calendar. ... Motto None (Unofficial: Broadly benefit humankind also translated as Devotion to the welfare of humanity) Anthem Aegukga Patriotic Hymn Capital (and largest city) Seoul Official languages Korean Government Presidential republic  -  President Roh Moo-hyun  -  Prime Minister Han Duck-soo Establishment  -  Liberation declared March 1, 1919 (de jure)   -  Liberation August 15... Samsung Electronics (SEC, Hangul:삼성전자; KSE: 005930, KSE: 005935, LSE: SMSN, LSE: SMSD) is a South Korean Multinational Corporation and one of the worlds largest Electronics and IT companies,[1]. In August 2005, BusinessWeek rated Samsung as the Number 1 consumer electronics brand in the world. ...


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.[14] Sandisk announced an OEM 32 GB 1.8" SSD drive at CES 2007.[15] The Las Vegas metropolitan area, includes the Las Vegas Valley a 600 square mile (1600 km²) basin, and surrounding areas, that are part of Clark County in southern Nevada. ... The International Consumer Electronics Show (CES) is a trade show held each January in Las Vegas, Nevada, and is sponsored by the Consumer Electronics Association. ... This article is about the history, geography, and people of the island known as Taiwan. ... It has been suggested that this article or section be merged with Solid state drive. ...


The XO-1, developed by the One Laptop Per Child (OLPC) association, uses flash memory rather than a hard drive. It has been suggested that this article be split into multiple articles. ... The $100 laptop is a design for an inexpensive laptop computer being developed by the One Laptop Per Child (OLPC) organization to provide every child in the world access to knowledge and modern forms of education. ...


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.[1] June 2007 is the sixth month of that year. ... MB, Mb, mB or mb may mean: Mb (digraph) Megabit (1,000,000 bits) or mebibit (220 = 1,048,576 bits); the preferred symbols are Mb and Mibit, respectively¹ Megabyte (1,000,000 bytes) or mebibyte (220 = 1,048,576 bytes); the preferred symbols are MB and MiB, respectively¹ MB...


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 operation system executable files. This article refers to the computer hard disk. ... ReadyBoost is a disk caching technology first included with Microsofts Windows Vista operating system. ... Look up cache in Wiktionary, the free dictionary. ...


See also

A 64 MB CompactFlash Type I card A 32 MB High Speed CompactFlash Type I card CompactFlash (CF) was originally developed as a type of data storage device used in portable electronic devices. ... Wear levelling (also written -leveling) is a technique for prolonging the service life of some kinds of erasable computer storage media, such as flash memory. ... DataFlash is a low pin-count serial interface for flash memory. ... The Open NAND Flash Interface Working Group, or ONFI, is a consortium of technology companies working to develop open standards for NAND flash memory chips and devices that communicate with them. ... This article needs to be cleaned up to conform to a higher standard of quality. ...

External links

References

  1. ^ SSD Myths and Legends
  2. ^ http://www.onfi.org/docs/ONFI_1_0_Gold.pdf
  3. ^ A list of ONFI members is available at http://www.onfi.org/onfimembers.html.
  4. ^ http://www.intel.com/pressroom/archive/releases/20070530corp.htm
  5. ^ a b c See pages 5-7 of Toshiba's "NAND Applications Design Guide" under External links.
  6. ^ Many serial flash devices implement a bulk read mode and incorporate an internal address counter, so that it is trivial to configure them to transfer their entire contents to RAM on power-up. When clocked at 50 MHz, for example, a serial flash could transfer a 64 Mbit firmware image in less than two seconds.
  7. ^ http://www.xbitlabs.com/news/memory/display/20050912212649.html
  8. ^ http://tgdaily.com/2006/09/11/samsung_40nm_flash/
  9. ^ http://www.pcnation.com/web/details.asp?affid=909&item=H76595
  10. ^ http://www.tgdaily.com/2005/09/13/bitmicro_rolls_out_155_gig_solid/
  11. ^ http://www.storagesearch.com/semico-art1.html
  12. ^ http://www.storagesearch.com/bitmicro-art1.html
  13. ^ http://www.samsung.com/he/presscenter/pressrelease/pressrelease_20060524_0000257996.asp
  14. ^ Future of Flash revealed
  15. ^ SanDisk SSD Solid State Drives

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