The notion of read-only data can also refer to file system permissions. Most modern File systems have methods of administering permissions or access rights to specific users and groups of users

Computer memory types

Volatile

DRAM, e. Volatile memory, also known as volatile storage or primary storage device, is Computer memory that requires power to maintain the stored information g. DDR SDRAM SRAM Upcoming Z-RAM TTRAM Historical Williams tube Delay line memory

Non-volatile

ROM PROM EAROM EPROM EEPROM Flash memory Upcoming FeRAM MRAM CBRAM PRAM SONOS RRAM Racetrack memory NRAM Historical Drum memory Magnetic core memory Bubble memory Twistor memory

Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. 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 Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed 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 Computer data storage, often called storage or memory, refers to Computer components devices and recording media that retain digital A computer is a Machine that manipulates data according to a list of instructions. Because data stored in ROM cannot be modified (at least not very quickly or easily), it is mainly used to distribute firmware (software that is very closely tied to specific hardware, and unlikely to require frequent updates). In Computing, firmware is a computer program that is Embedded in a hardware device for example a Microcontroller. Typical PC hardware A typical Personal computer consists of a case or chassis in a tower shape (desktop and the following parts Motherboard

Modern semiconductor ROM chips are not immediately distinguishable from similar chips like RAM modules, except by the part numbers printed on the package. A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside

In its strictest sense, ROM refers only to mask ROM (the oldest type of solid state ROM), which is fabricated with the desired data permanently stored in it, and thus can never be modified. Mask ROM (MROM refers to a kind of ROM (read-only memory whose contents are programmed by the Integrated circuit manufacturer (rather than by the user Solid-state Electronic components devices and systems are based entirely on the Semiconductor, such as Transistors Microprocessor chips and Semiconductor device fabrication is the process used to create chips the Integrated circuits that are present in everyday Electrical and electronic However, more modern types such as EPROM and flash EEPROM can be erased and re-programmed multiple times; they are still described as "read-only memory" because the reprogramming process is generally infrequent, comparatively slow, and often does not permit random access writes to individual memory locations, which are possible when reading a ROM. An EPROM, or E rasable P rogrammable '''''R'''ead-'''O'''nly '''M'''emory'', is a type of memory chip that retains its Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed In Computer science, random access (sometimes called direct access) is the ability to access an arbitrary element of a sequence in equal time Despite the simplicity of mask ROM, economies of scale and field-programmability often make reprogrammable technologies more flexible and inexpensive, so that mask ROM is rarely used in new products as of 2007. An electronic device or Embedded system is said to be field-programmable or in-place programmable if its Firmware (stored in Non-volatile Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.

Contents 1 History 1.1 Use of ROM for program storage 1.2 ROM for data storage 2 Types of ROMs 2.1 Semiconductor based 2.2 Other technologies 2.2.1 Historical examples 3 Speed of ROMs 3.1 Reading speed 3.2 Writing speed 4 Endurance and data retention 5 ROM images 6 See also 7 Terminology 8 References

History

The simplest type of solid state ROM is as old as semiconductor technology itself. Solid-state Electronic components devices and systems are based entirely on the Semiconductor, such as Transistors Microprocessor chips and Combinatorial logic gates can be joined manually to map n-bit address input onto arbitrary values of m-bit data output (a look-up table). In Digital circuit theory combinational logic (also called combinatorial logic) is a type of logic circuit whose output is a Pure function of the A logic gate performs a logical operation on one or more logic inputs and produces a single logic output In Computer science, a lookup table is a Data structure, usually an Array or Associative array, often used to replace a runtime computation with With the invention of the integrated circuit came mask ROM. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside Mask ROM (MROM refers to a kind of ROM (read-only memory whose contents are programmed by the Integrated circuit manufacturer (rather than by the user Mask ROM consists of a grid of word lines (the address input) and bit lines (the data output), selectively joined together with transistor switches, and can represent an arbitrary look-up table with a regular physical layout and predictable propagation delay. In Computing, " word " is a term for the natural unit of data used by a particular computer design Networking Propagation delay is defined as how long it takes for a certain amount of bytes to transfered over a medium

In mask ROM, the data is physically encoded in the circuit, so it can only be programmed during fabrication. This leads to a number of serious disadvantages:

1. It is only economical to buy mask ROM in large quantities, since users must contract with a foundry to produce a custom design. In the Microelectronics industry a semiconductor fabrication plant (commonly called a fab) is a factory where devices such as Integrated circuits are manufactured
2. The turnaround time between completing the design for a mask ROM and receiving the finished product is long, for the same reason.
3. Mask ROM is impractical for R&D work since designers frequently need to modify the contents of memora means to receive the program contents from an external source (e. The phrase research and development (also R and D or more often R&D) according to the Organization for Economic Co-operation and Development, refers g. a personal computer via a serial cable). A serial cable is a Cable that can be used to transfer information between two devices using Serial communication, often using the RS-232 standard Flash memory, invented at Toshiba in the mid-1980s, and commercialized in the early 1990s, is a form of EEPROM that makes very efficient use of chip area and can be erased and reprogrammed thousands of times without damage. Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed ( is a multinational conglomerate manufacturing company headquartered in Tokyo, Japan. EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable

All of these technologies improved the flexibility of ROM, but at a significant cost-per-chip, so that in large quantities mask ROM would remain an economical choice for many years. (Decreasing cost of reprogrammable devices had almost eliminated the market for mask ROM by the year 2000. 2000 ( MM) was a Leap year that started on Saturday of the Common Era, in accordance with the Gregorian calendar. ) Furthermore, despite the fact that newer technologies were increasingly less "read-only," most were envisioned only as replacements for the traditional use of mask ROM.

The most recent development is NAND flash, also invented by Toshiba. Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed Its designers explicitly broke from past practice, stating plainly that "the aim of NAND Flash is to replace hard disks,"^[1] rather than the traditional use of ROM as a form of non-volatile primary storage. A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device Computer data storage, often called storage or memory, refers to Computer components devices and recording media that retain digital As of 2007, NAND has partially achieved this goal by offering throughput comparable to hard disks, higher tolerance of physical shock, extreme miniaturization (in the form of USB flash drives and tiny microSD memory cards, for example), and much lower power consumption. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. microSD is a format for removable Flash memory cards It is derived from SanDisk TransFlash and is used mainly in mobile A memory card or flash memory card is a solid-state electronic Flash memory Data storage device used with Digital

Use of ROM for program storage

Every stored-program computer requires some form of non-volatile storage to store the initial program that runs when the computer is powered on or otherwise begins execution (a process known as bootstrapping, often abbreviated to "booting" or "booting up"). The von Neumann architecture is a design model for a stored-program Digital computer that uses a processing unit and a single separate storage structure 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 In computing bootstrapping ("to pull oneself up by one's bootstraps" refers to techniques that allow a simple system to activate a more complicated system In Computing, booting ( booting up) is a bootstrapping process that starts Operating systems when the user turns on a Computer system Likewise, every non-trivial computer requires some form of mutable memory to record changes in its state as it executes. In Computer science and Automata theory, a state is a unique configuration of information in a program or machine

Forms of read-only memory were employed as non-volatile storage for programs in most early stored-program computers, such as ENIAC after 1948 (until then it was not a stored-program computer as every problem had to be manually wired into the machine, which could take days to weeks). ENIAC, short for Electronic Numerical Integrator And Computer, was the first general-purpose electronic Computer. ENIAC, short for Electronic Numerical Integrator And Computer, was the first general-purpose electronic Computer. Read-only memory was simpler to implement since it required only a mechanism to read stored values, and not to change them in-place, and thus could be implemented with very crude electromechanical devices (see historical examples below). With the advent of integrated circuits in the 1960s, both ROM and its mutable counterpart static RAM were implemented as arrays of transistors in silicon chips; however, a ROM memory cell could be implemented using fewer transistors than an SRAM memory cell, since the latter requires a latch (comprising 5-20 transistors) to retain its contents, while a ROM cell might consist of a the absence (logical 0) or presence (logical 1) of a single transistor connecting a bit line to a word line. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside Static random access memory (SRAM is a type of Semiconductor memory where the word static indicates that unlike ''dynamic'' RAM (DRAM, it does not In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals In Electronics, a latch is a kind of Bistable Multivibrator, an Electronic circuit which has two stable states and thereby can store ^[2] Consequently, ROM could be implemented at a lower cost-per-bit than RAM for many years. 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

Many home computers of the 1980s stored a BASIC interpreter or operating system in ROM. A home computer was a class of Personal computer entering the market in 1977 and becoming common during the 1980s In Computer programming, BASIC (an Acronym for Beginner's All-purpose Symbolic Instruction Code) is a family of High-level programming languages An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination ROM was more economical than RAM, and other forms of non-volatile storage such as magnetic disk drives were too expensive to be included with every home computer. Magnetic storage and magnetic recording are terms from Engineering referring to the storage of Data on a Magnetized medium For example, the celebrated Commodore 64 included 64 KiB of RAM and 20 KiB of ROM contained a BASIC interpreter and the "KERNAL" (sic) of its operating system. A kibibyte (a contraction of ki lo bi nary byte) is a unit of Information or Computer storage, established by the International A kibibyte (a contraction of ki lo bi nary byte) is a unit of Information or Computer storage, established by the International This article is about Commodore's 8-bit OS software Kernal is also a common misspelling of Kernel. Later home or office computers such as the IBM PC XT often included magnetic disk drives, and larger amounts of RAM, allowing them to load their operating systems from disk into RAM, with only a minimal hardware initialization core and bootloader remaining in ROM (known as the BIOS in IBM-compatible computers). International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology The IBM Personal Computer XT, often shortened to the IBM XT or simply XT, was IBM's successor to the original IBM PC. In Computing, booting ( booting up) is a bootstrapping process that starts Operating systems when the user turns on a Computer system In Computing, the BIOS (ˈbaɪoʊs IBM PC compatible computers are those generally similar to the original IBM PC, XT, and AT. This arrangement allowed for a more complex and easily upgradeable operating system.

In modern general-purpose computers, there is little reason to store any program code or data in read-only memory: secondary storage devices such as hard disks are fast, ubiquitous, and rapidly decreasing in cost per bit, and large capacity dynamic RAM modules are cheaper than ROM thanks to economies of scale and more efficient designs. 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 hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device In modern PCs, ROM is used only to store basic bootstrapping firmware, such as the legacy BIOS which persists in most x86-based systems; even this limited "read-only" memory is likely to be implemented as Flash ROM (see below) to permit in-place reprogramming should the need for a firmware upgrade arise. In Computing, firmware is a computer program that is Embedded in a hardware device for example a Microcontroller. See also X86 assembly language The generic term x86 refers to the most commercially successful Instruction set architecture in the history of Personal

ROM and its successor technologies remain prevalent in embedded systems, such as MP3 players, set-top boxes, and broadband routers, all of which are designed to achieve more restricted functions than general-purpose computers, but which are nonetheless based on general-purpose microprocessors in most cases. 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 digital audio player, more commonly referred to as an MP3 player, is a Consumer electronics device that stores organizes and plays audio files Some 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 This article is about the types of network routers and modems found in many homes known colloquially as "residential gateways" A microprocessor incorporates most or all of the functions of a Central processing unit (CPU on a single Integrated These devices often store all of their program code in ROM since they usually lack mass storage peripherals (e. g. hard disks) for reasons of cost, portability, and power consumption. Furthermore, since the software is usually tightly coupled to the hardware, changes to the software are rarely needed. Nonetheless, as of 2007 nearly all of these devices use Flash rather than mask ROM, and many provide some means to connect the device to a personal computer for firmware updates (for example, a digital audio player's firmware might be updated to support a new music file format). Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. In Computing, firmware is a computer program that is Embedded in a hardware device for example a Microcontroller. A file format is a particular way to encode information for storage in a Computer file. Hobbyists have taken advantage of this flexibility to reprogram such devices to new purposes; for example, the iPodLinux and OpenWRT projects have enabled users to run full-featured Linux distributions on their MP3 players and wireless routers, respectively. iPodLinux is a µClinux -based Linux distribution targeted specifically to run on Apple Inc OpenWrt is a Linux -based Firmware program for embedded devices such as Residential gateways Support was originally limited to the Linux (commonly pronounced ˈlɪnəks A Linux distribution (also called GNU/Linux by distributions such as Debian, Fedora, Ubuntu, Linux Mint, Mandriva and

ROM is also useful for binary storage of cryptographic data, as it makes them difficult to replace, which may be desirable in order to enhance information security. Cryptography (or cryptology; from Greek grc κρυπτός kryptos, "hidden secret" and grc γράφω gráphō, "I write" Information security means protecting information and information systems from unauthorized access use disclosure disruption modification or destruction

ROM for data storage

Since ROM (at least in hard-wired mask form) cannot be modified, it is really only suitable for storing data which is not expected to need modification for the life of the device. To that end, ROM has been used in many computers to store look-up tables for the evaluation of mathematical and logical functions (for example, a floating-point unit might tabulate the sine function in order to facilitate faster computation). In Computer science, a lookup table is a Data structure, usually an Array or Associative array, often used to replace a runtime computation with A floating point unit (FPU is a part of a Computer system specially designed to carry out operations on Floating point numbers In Computer science, a lookup table is a Data structure, usually an Array or Associative array, often used to replace a runtime computation with This was especially effective when CPUs were slow and ROM was cheap compared to RAM.

Notably, the display adapters of early personal computers stored tables of bitmapped font characters in ROM. A video card, also known as a graphics accelerator card, display adapter, or graphics card, is a hardware component whose function is to This usually meant that the text display font could not be changed interactively. In typography a font (also fount) is traditionally defined as a complete character set of a single size and style of a particular Typeface. This was the case for both the CGA and MDA adapters available with the IBM PC XT. The Color Graphics Adapter ( CGA) originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter The Monochrome Display Adapter ( MDA, also MDA card, Monochrome Display and Printer Adapter, MDPA) introduced in 1981 was IBM

The use of ROM to store such small amounts of data has disappeared almost completely in modern general-purpose computers. However, Flash ROM has taken over a new role as a medium for mass storage or secondary storage of files . In Computing, mass storage refers to the storage of large amounts of information in a persisting and Machine-readable fashion Computer data storage, often called storage or memory, refers to Computer components devices and recording media that retain digital

Types of ROMs

Semiconductor based

Classic mask-programmed ROM chips are integrated circuits that physically encode the data to be stored, and thus it is impossible to change their contents after fabrication. Other types of non-volatile solid-state memory permit some degree of modification:

• Programmable read-only memory (PROM), or one-time programmable ROM (OTP), can be written to or programmed via a special device called a PROM programmer. 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 Typically, this device uses high voltages to permanently destroy or create internal links (fuses or antifuses) within the chip. In Electronics and Electrical engineering a fuse (short for fusible link) is a type of Overcurrent protection device An antifuse is an electrical device that performs the opposite function to a fuse. Consequently, a PROM can only be programmed once.
• Erasable programmable read-only memory (EPROM) can be erased by exposure to strong ultraviolet light (typically for 10 minutes or longer), then rewritten with a process that again requires application of higher than usual voltage. An EPROM, or E rasable P rogrammable '''''R'''ead-'''O'''nly '''M'''emory'', is a type of memory chip that retains its Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Repeated exposure to UV light will eventually wear out an EPROM, but the endurance of most EPROM chips exceeds 1000 cycles of erasing and reprogramming. EPROM chip packages can often be identified by the prominent quartz "window" which allows UV light to enter. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in After programming, the window is typically covered with a label to prevent accidental erasure. Some EPROM chips are factory-erased before they are packaged, and include no window; these are effectively PROM.
• Electrically erasable programmable read-only memory (EEPROM) is based on a similar semiconductor structure to EPROM, but allows its entire contents (or selected banks) to be electrically erased, then rewritten electrically, so that they need not be removed from the computer (or camera, MP3 player, etc. EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable ). Writing or flashing an EEPROM is much slower (milliseconds per bit) than reading from a ROM or writing to a RAM (nanoseconds in both cases).
  • Electrically alterable read-only memory (EAROM) is a type of EEPROM that can be modified one bit at a time. EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable 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 Writing is a very slow process and again requires higher voltage (usually around 12 V) than is used for read access. The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. EAROMs are intended for applications that require infrequent and only partial rewriting. EAROM may be used as non-volatile storage for critical system setup information; in many applications, EAROM has been supplanted by CMOS RAM supplied by mains power and backed-up with a lithium battery. Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is Computer memory that can retain the stored information Complementary metal–oxide–semiconductor ( CMOS) (pronounced "see-moss" siːmɔːs ˈsiːmɒs is a major class of Integrated circuits CMOS technology Mains is the general-purpose Alternating current (AC Electric power supply (as in "I've connected the appliance to the mains" Lithium batteries are not to be confused with lithium-ion batteries which are high energy-density rechargeable batteries Lithium batteries are
  • Flash memory (or simply flash) is a modern type of EEPROM invented in 1984. Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed Year 1984 ( MCMLXXXIV) was a Leap year starting on Sunday (link displays the 1984 Gregorian calendar) Flash memory can be erased and rewritten faster than ordinary EEPROM, and newer designs feature very high endurance (exceeding 1,000,000 cycles). Modern NAND flash makes efficient use of silicon chip area, resulting in individual ICs with a capacity as high as 16 GB as of 2007; this feature, along with its endurance and physical durability, has allowed NAND flash to replace magnetic in some applications (such as USB flash drives). Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Magnetic storage and magnetic recording are terms from Engineering referring to the storage of Data on a Magnetized medium Flash memory is sometimes called flash ROM or flash EEPROM when used as a replacement for older ROM types, but not in applications that take advantage of its ability to be modified quickly and frequently.

By applying write protection, some types of reprogrammable ROMs may temporarily become read-only memory. Write protection is any physical mechanism that prevents modification or erasure of valuable Data on a device

Other technologies

There are other types of non-volatile memory which are not based on solid-state IC technology, including:

• Optical storage media, such CD-ROM which is read-only (analogous to masked ROM). Optical storage is a term from Engineering referring to the storage of data on an optically readable medium CD-ROM (an initialism of "Compact Disc Read-Only Memory " is a pre-pressed Compact Disc that contains data accessible to but not writable CD-R is Write Once Read Many (analogous to PROM), while CD-RW supports erase-rewrite cycles (analogous to EEPROM); both are designed for backwards-compatibility with CD-ROM. A CD-R ( C ompact D isc- R ecordable is a variation of the Compact Disc invented by Philips and Sony. Write Once Read Many (alternatively Write One Read Multiple or Write Once Read Mostly or WORM) refers to Computer data storage systems Compact Disc ReWritable (CD-RW is a rewritable Optical disc format In Technology, especially Computing (irrespective of platform a product is said to be backward compatible when it is able to take the place of an older product

Historical examples

• Diode matrix ROM, used in small amounts in many computers in the 1960s as well as electronic desk calculators and keyboard encoders for terminals. Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes The 1960s decade refers to the years from the beginning of 1960 to the end of 1969 A calculator is device for performing mathematical calculations distinguished from a Computer by having a limited problem solving ability and an interface optimized for interactive A computer terminal is an electronic or electromechanical hardware device that is used for entering data into and displaying data from a Computer or a Computing This ROM was programmed by installing discrete semiconductor diodes at selected locations between a matrix of word line traces and bit line traces on a printed circuit board. A printed circuit board, or PCB, is used to mechanically support and electrically connect Electronic components using conductive pathways or traces
• Resistor, capacitor, or transformer matrix ROM, used in many computers until the 1970s. |- align = "center"| |width = "25"| | |- align = "center"| || Potentiometer |- align = "center"| | | |- align = "center"| Resistor| | A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors This article is about the Decade 1970-1979 For the Year 1970 see 1970. Like diode matrix ROM, it was programmed by placing components at selected locations between a matrix of word lines and bit lines. ENIAC's Function Tables were resistor matrix ROM, programmed by manually setting rotary switches. ENIAC, short for Electronic Numerical Integrator And Computer, was the first general-purpose electronic Computer. Various models of the IBM System/360 and complex peripherial devices stored their microcode in either capacitor (called BCROS for Balanced Capacitor Read Only Storage on the 360/50 & 360/65 or CCROS for Card Capacitor Read Only Storage on the 360/30) or transformer (called TROS for Transformer Read Only Storage on the 360/20, 360/40 and others) matrix ROM. International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology The IBM System/360 ( S/360) is a Mainframe computer system family announced by IBM on April 7, 1964. Microprogramming (ie writing microcode) is a method that can be employed to implement Machine instructions in a CPU relatively easily often using less
• Core rope, a form of transformer matrix ROM technology used where size and/or weight were critical. Core rope memory is a form of Read-only memory (ROM for Computers first used by early NASA Mars probes and then in the Apollo This was used in NASA/MIT's Apollo Spacecraft Computers, DEC's PDP-8 computers, and other places. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program Digital Equipment Corporation was a pioneering American company in the Computer industry The PDP-8 was the first successful commercial Minicomputer, produced by Digital Equipment Corporation (DEC in the 1960s This type of ROM was programmed by hand by weaving "word line wires" inside or outside of ferrite transformer cores. Ferrites are a class of Chemical compounds with the formula AB2O4 where A and B represent various metal Cations usually including
• The perforated metal character mask ("stencil") in Charactron cathode ray tubes, which was used as ROM to shape a wide electron beam to form a selected character shape on the screen either for display or a scanned electron beam to form a selected character shape as an overlay on a video signal. A stencil is a Template used to draw or paint identical letters, Symbols, Shapes or Patterns every Charactron was U S registered trademark (number 0585950 23 February 1954 by Consolidated Vultee Aircraft Corporation ( Convair) for its shaped electron beam Cathode ray The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or Cathode rays (also called an electron beam or e-beam) are streams of Electrons observed in Vacuum tubes i Video is the technology of electronically capturing, Recording, processing storing transmitting and reconstructing a sequence of Still images
• Various mechanical devices used in early computing equipment. A machined metal plate served as ROM in the dot matrix printers on the IBM 026 and IBM 029 key punches. A dot matrix printer or impact matrix printer refers to a type of Computer printer with a print head that runs back and forth on the page and prints by impact striking A key punch is a device for entering data into Punched cards by precisely punching holes at locations designated by the keys struck by the operator A key punch is a device for entering data into Punched cards by precisely punching holes at locations designated by the keys struck by the operator A key punch is a device for entering data into Punched cards by precisely punching holes at locations designated by the keys struck by the operator

Speed of ROMs

Reading speed

Although the relative speed of RAM vs. ROM has varied over time, as of 2007 large RAM chips can be read faster than most ROMs. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. For this reason (and to make for uniform access), ROM content is sometimes copied to RAM or shadowed before its first use, and subsequently read from RAM.

Writing speed

For those types of ROM that can be electrically modified, writing speed is always much slower than reading speed, and it may require unusually high voltage, the movement of jumper plugs to apply write-enable signals, and special lock/unlock command codes. Modern NAND Flash achieves the highest write speeds of any rewritable ROM technology, with speeds as high as 15 MiB/s (or 70 ns/bit), by allowing (indeed requiring) large blocks of memory cells to be written simultaneously. A mebibyte (a contraction of me ga bi nary byte) is a unit of Information or Computer storage, abbreviated MiB. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units A nanosecond ( ns) is one billionth of a second See also times of other orders of magnitude.

Endurance and data retention

Because they are written by forcing electrons through a layer of electrical insulation onto a floating transistor gate, rewriteable ROMs can withstand only a limited number of write and erase cycles before the insulation is permanently damaged. An insulator, also called a Dielectric, is a material that resists the flow of Electric current. In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals In the earliest EAROMs, this might occur after as few as 1,000 write cycles, while in modern Flash EEPROM the endurance may exceed 1,000,000, but it is by no means infinite. This limited endurance, as well as the higher cost per bit, means that Flash-based storage is unlikely to completely supplant magnetic disk drives in the near future. Disk storage is a general category of a Computer storage mechanisms in which data is recorded on planar round and rotating surfaces ( disks, discs, or

The timespan over which a ROM remains accurately readable is not limited by write cycling. The data retention of EPROM, EAROM, EEPROM, and Flash may be limited by charge leaking from the floating gates of the memory cell transistors. The floating gate transistor is a kind of Transistor that is commonly used for Non-volatile storage such as flash, EPROM and EEPROM Leakage is exacerbated at high temperatures or in high-radiation environments. Image talkNew_radiation_symbol_ISO_21482svg for details --> Ionizing radiation Masked ROM and fuse/antifuse PROM do not suffer from this effect, as their data retention depends on physical rather than electrical permanence of the integrated circuit (although fuse re-growth was once a problem in some systems).

ROM images

Main article: ROM image

The contents of ROM chips in video game console cartridges can be extracted with special software or hardware devices. A ROM image, or simply ROM, is a computer file which contains a copy of the data from a Read-only memory chip often from a video game cartridge, a In various types of electronic equipment a cartridge can refer one method of adding different functionality or content (e The resultant memory dump files are known as ROM images, and can be used to produce duplicate cartridges, or in console emulators. A console emulator is a program that allows a computer or modern console (cross-console emulation to emulate a Video game console. The term originated when most console games were distributed on cartridges containing ROM chips, but achieved such widespread usage that it is still applied to images of newer games distributed on CD-ROMs or other optical media. CD-ROM (an initialism of "Compact Disc Read-Only Memory " is a pre-pressed Compact Disc that contains data accessible to but not writable

ROM images of commercial games usually contain copyrighted software. The unauthorized copying and distribution of copyrighted software is usually a violation of copyright laws (in some jurisdictions duplication of ROM cartridges for backup purposes may be considered fair use). Copyright is a legal concept enacted by Governments, giving the creator of an original work of authorship Exclusive rights to control its distribution usually for In Law, jurisdiction (from the Latin ius iuris meaning "law" and dicere meaning "to speak" is the practical Authority In Information technology, backup refers to making copies of Data so that these additional copies may be used to restore the original after a Fair use is a doctrine in United States copyright law that allows limited use of copyrighted material without requiring permission from the rights holders such as use for Nevertheless, there is a thriving community engaged in the illegal distribution and trading of such software. In such circles, the term "ROM images" is sometimes shortened simply to "ROMs" or sometimes changed to "romz" to highlight the connection with "warez". "Warez" refers primarily to Copyrighted works traded in violation of Copyright law.

See also

• Random access memory
• PROM
• EPROM
• EEPROM
• Flash memory

Terminology

EEPROM

Electrically Erasable Programmable Read-Only Memory

EPROM

Erasable Programmable Read-Only Memory

PROM

Programmable read-only memory

References

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