Flash memory
Flash memory is an electronic non-volatile computer storage medium that can be electrically erased and reprogrammed. Toshiba developed flash memory from EEPROM in the early 1980s and introduced it to the market in 1984; the two main types of flash memory are named after the NOR logic gates. The individual flash memory cells exhibit internal characteristics similar to those of the corresponding gates. While EPROMs had to be erased before being rewritten, NAND-type flash memory may be written and read in blocks which are much smaller than the entire device. NOR-type flash allows a single machine word to be written – to an erased location – or read independently; the NAND type is found in memory cards, USB flash drives, solid-state drives, similar products, for general storage and transfer of data. NAND or NOR flash memory is often used to store configuration data in numerous digital products, a task made possible by EEPROM or battery-powered static RAM. One key disadvantage of flash memory is that it can only endure a small number of write cycles in a specific block.
Example applications of both types of flash memory include personal computers, PDAs, digital audio players, digital cameras, mobile phones, video games, scientific instrumentation, industrial robotics, medical electronics. In addition to being non-volatile, flash memory offers fast read access times, although not as fast as static RAM or ROM, its mechanical shock resistance helps explain its popularity over hard disks in portable devices, as does its high durability, ability to withstand high pressure and immersion in water, etc. Although flash memory is technically a type of EEPROM, the term "EEPROM" is used to refer to non-flash EEPROM, erasable in small blocks bytes; because erase cycles are slow, the large block sizes used in flash memory erasing give it a significant speed advantage over non-flash EEPROM when writing large amounts of data. As of 2013, flash memory costs much less than byte-programmable EEPROM and had become the dominant memory type wherever a system required a significant amount of non-volatile solid-state storage.
Flash memory was invented by Fujio Masuoka while working for Toshiba circa 1980. According to Toshiba, the name "flash" was suggested by Masuoka's colleague, Shōji Ariizumi, because the erasure process of the memory contents reminded him of the flash of a camera. Masuoka and colleagues presented the invention at the IEEE 1987 International Electron Devices Meeting held in San Francisco. Intel Corporation introduced the first commercial NOR type flash chip in 1988. NOR-based flash has long erase and write times, but provides full address and data buses, allowing random access to any memory location; this makes it a suitable replacement for older read-only memory chips, which are used to store program code that needs to be updated, such as a computer's BIOS or the firmware of set-top boxes. Its endurance may be from as little as 100 erase cycles for an on-chip flash memory, to a more typical 10,000 or 100,000 erase cycles, up to 1,000,000 erase cycles. NOR-based flash was the basis of early flash-based removable media.
NAND flash has reduced erase and write times, requires less chip area per cell, thus allowing greater storage density and lower cost per bit than 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 as a drop-in replacement for program ROM, since most microprocessors and microcontrollers require byte-level random access. In this regard, NAND flash is similar to other secondary data storage devices, such as hard disks and optical media, is thus suitable for use in mass-storage devices, such as memory cards; the first NAND-based removable media format was SmartMedia in 1995, many others have followed, including: MultiMediaCard Secure Digital Memory Stick, xD-Picture Card. A new generation of memory card formats, including RS-MMC, miniSD and microSD, feature small form factors. For example, the microSD card has an area of just over 1.5 cm2, with a thickness of less than 1 mm.
As of August 2017 microSD cards with capacity up to 400 GB are available. Flash memory stores information in an array of memory cells made from floating-gate transistors. In single-level cell devices, each cell stores only one bit of information. Multi-level cell devices, including triple-level cell devices, can store more than one bit per cell; the floating gate may be non-conductive. In flash memory, each memory cell resembles a standard metal-oxide-semiconductor field-effect transistor except that the transistor has two gates instead of one; the cells can be seen as an electrical switch in which current flows between two terminals and is controlled by a floating gate and a control gate. The CG is similar to the gate in other MOS transistors, but below this, there is the FG insulated all around by an oxide layer; the FG is interposed between the MOSFET channel. Because the FG is electrically isolated by its insulating layer, electrons placed on it are trapped; when the FG is charged with electrons, this charge screens the electric field from the CG, inc
Floppy disk
A floppy disk known as a floppy, diskette, or disk, is a type of disk storage composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic enclosure lined with fabric that removes dust particles. Floppy disks are written by a floppy disk drive. Floppy disks as 8-inch media and in 5 1⁄4-inch and 3 1⁄2 inch sizes, were a ubiquitous form of data storage and exchange from the mid-1970s into the first years of the 21st century. By 2006 computers were manufactured with installed floppy disk drives; these formats are handled by older equipment. The prevalence of floppy disks in late-twentieth century culture was such that many electronic and software programs still use the floppy disks as save icons. While floppy disk drives still have some limited uses with legacy industrial computer equipment, they have been superseded by data storage methods with much greater capacity, such as USB flash drives, flash storage cards, portable external hard disk drives, optical discs, cloud storage and storage available through computer networks.
The first commercial floppy disks, developed in the late 1960s, were 8 inches in diameter. These disks and associated drives were produced and improved upon by IBM and other companies such as Memorex, Shugart Associates, Burroughs Corporation; the term "floppy disk" appeared in print as early as 1970, although IBM announced its first media as the "Type 1 Diskette" in 1973, the industry continued to use the terms "floppy disk" or "floppy". In 1976, Shugart Associates introduced the 5 1⁄4-inch FDD. By 1978 there were more than 10 manufacturers producing such FDDs. There were competing floppy disk formats, with hard- and soft-sector versions and encoding schemes such as FM, MFM, M2FM and GCR; the 5 1⁄4-inch format displaced the 8-inch one for most applications, the hard-sectored disk format disappeared. The most common capacity of the 5 1⁄4-inch format in DOS-based PCs was 360 KB, for the DSDD format using MFM encoding. In 1984 IBM introduced with its PC-AT model the 1.2 MB dual-sided 5 1⁄4-inch floppy disk, but it never became popular.
IBM started using the 720 KB double-density 3 1⁄2-inch microfloppy disk on its Convertible laptop computer in 1986 and the 1.44 MB high-density version with the PS/2 line in 1987. These disk drives could be added to older PC models. In 1988 IBM introduced a drive for 2.88 MB "DSED" diskettes in its top-of-the-line PS/2 models, but this was a commercial failure. Throughout the early 1980s, limitations of the 5 1⁄4-inch format became clear. Designed to be more practical than the 8-inch format, it was itself too large. A number of solutions were developed, with drives at 2-, 2 1⁄2-, 3-, 3 1⁄4-, 3 1⁄2- and 4-inches offered by various companies, they all shared a number of advantages over the old format, including a rigid case with a sliding metal shutter over the head slot, which helped protect the delicate magnetic medium from dust and damage, a sliding write protection tab, far more convenient than the adhesive tabs used with earlier disks. The large market share of the well-established 5 1⁄4-inch format made it difficult for these diverse mutually-incompatible new formats to gain significant market share.
A variant on the Sony design, introduced in 1982 by a large number of manufacturers, was rapidly adopted. The term floppy disk persisted though style floppy disks have a rigid case around an internal floppy disk. By the end of the 1980s, 5 1⁄4-inch disks had been superseded by 3 1⁄2-inch disks. During this time, PCs came equipped with drives of both sizes. By the mid-1990s, 5 1⁄4-inch drives had disappeared, as the 3 1⁄2-inch disk became the predominant floppy disk; the advantages of the 3 1⁄2-inch disk were its higher capacity, its smaller size, its rigid case which provided better protection from dirt and other environmental risks. If a person touches the exposed disk surface of a 5 1⁄4-inch disk through the drive hole, fingerprints may foul the disk—and the disk drive head if the disk is subsequently loaded into a drive—and it is easily possible to damage a disk of this type by folding or creasing it rendering it at least unreadable; however due to its simpler construction the 5 1⁄4-inch disk unit price was lower throughout its history in the range of a third to a half that of a 3 1⁄2-inch disk.
Floppy disks became commonplace during the 1980s and 1990s in their use with personal computers to distribute software, transfer data, create backups. Before hard disks became affordable to the general population, floppy disks were used to store a computer's operating system. Most home computers from that period have an elementary OS and BASIC stored in ROM, with the option of loading a more advanced operating system from a floppy disk. By the early 1990s, the increasing software size meant large packages like Windows or Adobe Photoshop required a dozen disks or more. In 1996, there were an estimated five billion standard floppy disks in use. Distribution of larger packages was replaced by CD-ROMs, DVDs and online distribution. An
Nano-RAM
Nano-RAM is a proprietary computer memory technology from the company Nantero. It is a type of nonvolatile random access memory based on the position of carbon nanotubes deposited on a chip-like substrate. In theory, the small size of the nanotubes allows for high density memories. Nantero refers to it as NRAM; the first generation Nantero NRAM technology was based on a three-terminal semiconductor device where a third terminal is used to switch the memory cell between memory states. The second generation NRAM technology is based on a two-terminal memory cell; the two-terminal cell has advantages such as a smaller cell size, better scalability to sub-20 nm nodes, the ability to passivate the memory cell during fabrication. In a non-woven fabric matrix of carbon nanotubes, crossed nanotubes can either be touching or separated depending on their position; when touching, the carbon nanotubes are held together by Van der Waals forces. Each NRAM "cell" consists of an interlinked network of CNTs located between two electrodes as illustrated in Figure 1.
The CNT fabric is located between two metal electrodes, defined and etched by photolithography, forms the NRAM cell. The NRAM acts as a resistive non-volatile random access memory and can be placed in two or more resistive modes depending on the resistive state of the CNT fabric; when the CNTs are not in contact the resistance state of the fabric is high and represents an "off" or "0" state. When the CNTs are brought into contact, the resistance state of the fabric is low and represents an "on" or "1" state. NRAM acts as a memory because the two resistive states are stable. In the 0 state, the CNTs are not in contact and remain in a separated state due to the stiffness of the CNTs resulting in a high resistance or low current measurement state between the top and bottom electrodes. In the 1 state, the CNTs are in contact and remain contacted due to Van der Waals forces between the CNTs, resulting in a low resistance or high current measurement state between the top and bottom electrodes. Note that other sources of resistance such as contact resistance between electrode and CNT can be significant and need to be considered.
To switch the NRAM between states, a small voltage greater than the read voltage is applied between top and bottom electrodes. If the NRAM is in the 0 state, the voltage applied will cause an electrostatic attraction between the CNTs close to each other causing a SET operation. After the applied voltage is removed, the CNTs remain in a 1 or low resistance state due to physical adhesion with an activation energy of 5eV. If the NRAM cell is in the 1 state, applying a voltage greater than the read voltage will generate CNT phonon excitations with sufficient energy to separate the CNT junctions; this is the phonon driven RESET operation. The CNTs remain in the OFF or high resistance state due to the high mechanical stiffness with an activation energy much greater than 5 eV. Figure 2 illustrates both states of an individual pair of CNTs involved in the switch operation. Due to the high activation energy required for switching between states, the NRAM switch resists outside interference like radiation and operating temperature that can erase or flip conventional memories like DRAM.
NRAMs are fabricated by depositing a uniform layer of CNTs onto a prefabricated array of drivers such as transistors as shown in Figure 1. The bottom electrode of the NRAM cell is in contact with the underlying via connecting the cell to the driver; the bottom electrode may be fabricated as part of the underlying via or it may be fabricated with the NRAM cell, when the cell is photolithographically defined and etched. Before the cell is photolithographically defined and etched, the top electrode is deposited as a metal film onto the CNT layer so that the top metal electrode is patterned and etched during the definition of the NRAM cell. Following the dielectric passivation and fill of the array, the top metal electrode is exposed by etching back the overlying dielectric using a smoothing process such as chemical-mechanical planarization. With the top electrode exposed, the next level of metal wiring interconnect is fabricated to complete the NRAM array. Figure 3 illustrates one circuit method to select a single cell for reading.
Using a cross-grid interconnect arrangement, the NRAM and driver, forms a memory array similar to other memory arrays. A single cell can be selected by applying the proper voltages to the word line, bit line, select lines without disturbing the other cells in the array. NRAM has a density, at least in theory, similar to that of DRAM. DRAM includes capacitors, which are two small metal plates with a thin insulator between them. NRAM has terminals and electrodes the same size as the plates in a DRAM, the nanotubes between them being so much smaller they add nothing to the overall size; however it seems there is a minimum size at which a DRAM can be built, below which there is not enough charge being stored on the plates. NRAM appears to be limited only by lithography; this means that NRAM may be able to become much denser than DRAM also less expensive. Unlike DRAM, NRAM does not require power to "refresh" it, will retain its memory after power is removed, thus the power needed to write and retain the memory state of the device is much lower than DRAM, which has to build up charge on the cell plates.
This means that NRAM might compete with DRAM in terms of cost, but require less power, as a result be much faster because write performance is determin
Random-access memory
Random-access memory is a form of computer data storage that stores data and machine code being used. A random-access memory device allows data items to be read or written in the same amount of time irrespective of the physical location of data inside the memory. In contrast, with other direct-access data storage media such as hard disks, CD-RWs, DVD-RWs and the older magnetic tapes and drum memory, the time required to read and write data items varies depending on their physical locations on the recording medium, due to mechanical limitations such as media rotation speeds and arm movement. RAM contains multiplexing and demultiplexing circuitry, to connect the data lines to the addressed storage for reading or writing the entry. More than one bit of storage is accessed by the same address, RAM devices have multiple data lines and are said to be "8-bit" or "16-bit", etc. devices. In today's technology, random-access memory takes the form of integrated circuits. RAM is associated with volatile types of memory, where stored information is lost if power is removed, although non-volatile RAM has been developed.
Other types of non-volatile memories exist that allow random access for read operations, but either do not allow write operations or have other kinds of limitations on them. These include most types of ROM and a type of flash memory called NOR-Flash. Integrated-circuit RAM chips came into the market in the early 1970s, with the first commercially available DRAM chip, the Intel 1103, introduced in October 1970. Early computers used relays, mechanical counters or delay lines for main memory functions. Ultrasonic delay lines could only reproduce data in the order. Drum memory could be expanded at low cost but efficient retrieval of memory items required knowledge of the physical layout of the drum to optimize speed. Latches built out of vacuum tube triodes, out of discrete transistors, were used for smaller and faster memories such as registers; such registers were large and too costly to use for large amounts of data. The first practical form of random-access memory was the Williams tube starting in 1947.
It stored data. Since the electron beam of the CRT could read and write the spots on the tube in any order, memory was random access; the capacity of the Williams tube was a few hundred to around a thousand bits, but it was much smaller and more power-efficient than using individual vacuum tube latches. Developed at the University of Manchester in England, the Williams tube provided the medium on which the first electronically stored program was implemented in the Manchester Baby computer, which first ran a program on 21 June 1948. In fact, rather than the Williams tube memory being designed for the Baby, the Baby was a testbed to demonstrate the reliability of the memory. Magnetic-core memory was developed up until the mid-1970s, it became a widespread form of random-access memory. By changing the sense of each ring's magnetization, data could be stored with one bit stored per ring. Since every ring had a combination of address wires to select and read or write it, access to any memory location in any sequence was possible.
Magnetic core memory was the standard form of memory system until displaced by solid-state memory in integrated circuits, starting in the early 1970s. Dynamic random-access memory allowed replacement of a 4 or 6-transistor latch circuit by a single transistor for each memory bit increasing memory density at the cost of volatility. Data was stored in the tiny capacitance of each transistor, had to be periodically refreshed every few milliseconds before the charge could leak away; the Toshiba Toscal BC-1411 electronic calculator, introduced in 1965, used a form of DRAM built from discrete components. DRAM was developed by Robert H. Dennard in 1968. Prior to the development of integrated read-only memory circuits, permanent random-access memory was constructed using diode matrices driven by address decoders, or specially wound core rope memory planes; the two used forms of modern RAM are static RAM and dynamic RAM. In SRAM, a bit of data is stored using the state of a six transistor memory cell.
This form of RAM is more expensive to produce, but is faster and requires less dynamic power than DRAM. In modern computers, SRAM is used as cache memory for the CPU. DRAM stores a bit of data using a transistor and capacitor pair, which together comprise a DRAM cell; the capacitor holds a high or low charge, the transistor acts as a switch that lets the control circuitry on the chip read the capacitor's state of charge or change it. As this form of memory is less expensive to produce than static RAM, it is the predominant form of computer memory used in modern computers. Both static and dynamic RAM are considered volatile, as their state is lost or reset when power is removed from the system. By contrast, read-only memory stores data by permanently enabling or disabling selected transistors, such that the memory cannot be altered. Writeable variants of ROM share properties of both ROM and RAM, enabling data to persist without power and to be updated without requiring special equipment; these persistent forms of semiconductor ROM include USB flash drives, memory cards for cameras and portable devices, solid-state drives.
ECC memory includes special circuitry to detect and/or correct random faults (mem
Disk pack
Disk packs and disk cartridges were early forms of removable media for computer data storage, introduced in the 1960s. A Disk pack is a layered grouping of hard disk platters. A disk pack is the core component of a hard disk drive. In modern hard disks, the disk pack is permanently sealed inside the drive. In many early hard disks, the disk pack was a removable unit, would be supplied with a protective canister featuring a lifting handle; the protective cover consisted of two parts, a plastic shell, with a handle in the center, that enclosed the top and sides of the disks and a separate bottom that completed the sealed package. To remove the disk pack, the drive would be allowed to spin down, its access door could be opened and an empty shell inserted and twisted to unlock the disk platter from the drive and secure it to the shell. The assembly would be lifted out and the bottom cover attached. A different disk pack could be inserted by removing the bottom and placing the disk pack with its shell into the drive.
Turning the handle would lock the disk pack in place and free the shell for removal. The first removable disk pack was invented in 1961 by IBM engineers R. E. Pattison as part of the LCF project headed by Jack Harker; the 14-inch diameter disks introduced by IBM became a de facto standard, with many vendors producing disk drives using 14-inch disks in disk packs and cartridges into the 1980s. Examples of disk drives that employed removable disk packs include the IBM 1311, IBM 2311, the Digital RP04. An early disk cartridge was a single hard disk platter encased in a protective plastic shell; when the removable cartridge was inserted into the cartridge drive peripheral device, the read/write heads of the drive could access the magnetic data storage surface of the platter through holes in the shell. The disk cartridge was the early hard drive; as the storage density improved a single platter would provide a useful amount of data storage space, with the benefit being easier to handle than a removable disk pack.
An example of a cartridge drive is the IBM 2310, used on the IBM 1130. Disk cartridges were made obsolete by floppy disks. Disk drives with exchangeable disk packs or disk cartridges required the data heads to be aligned to allow packs formatted on one drive to be read and written on another compatible drive. Alignment required a special alignment pack, an oscilloscope, an alignment tool that moved the read/write heads, patience; the pattern generated on the scope looks like a row of alternating C and E characters on their backs. Head alignment needed to be performed after head replacement, in any case on a periodic basis as part of the routine maintenance required by the drives; the alignment pack was called the "CE pack," because IBM never called their'service technicians"repairmen,' but "Customer Engineers". And, since the alignment pack was only to be used by CEs, it was called the "CE Pack." Special CE media was available for tape drives and diskette drives, known as "the CE tape" and "the CE floppy."
Drives with exchangeable packs embedded the servo with the data and didn't require regular head alignment. History of hard disk drives IBM 1311 disk storage drive, IBM Archives Thomas G. Leary, "Transporting and Protecting Cases for Drum and Disk Records," U. S. Patent 3,206,214, 1965. E. Pattison, "Portable Memory for Data Processing Machine," U. S. Patent 3,176,281, 1965
Read-only memory
Read-only memory is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM can only be modified with difficulty, or not at all, so it is used to store firmware or application software in plug-in cartridges. Read-only memory refers to memory, hard-wired, such as diode matrix and the mask ROM, which cannot be changed after manufacture. Although discrete circuits can be altered in principle, integrated circuits cannot, are useless if the data is bad or requires an update; that such memory can never be changed is a disadvantage in many applications, as bugs and security issues cannot be fixed, new features cannot be added. More ROM has come to include memory, read-only in normal operation, but can still be reprogrammed in some way. Erasable programmable read-only memory and electrically erasable programmable read-only memory can be erased and re-programmed, but this can only be done at slow speeds, may require special equipment to achieve, is only possible a certain number of times.
IBM used Capacitor Read Only Storage and Transformer Read Only Storage to store microcode for the smaller System/360 models, the 360/85 and the initial two models of the S/370. On some models there was a Writeable Control Store for additional diagnostics and emulation support; the simplest type of solid-state ROM is as old as the semiconductor technology itself. Combinational logic gates can be joined manually to map n-bit address input onto arbitrary values of m-bit data output. With the invention of the integrated circuit came mask ROM. Mask ROM consists of a grid of word lines and bit lines, selectively joined together with transistor switches, can represent an arbitrary look-up table with a regular physical layout and predictable propagation delay. 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: It is only economical to buy mask ROM in large quantities, since users must contract with a foundry to produce a custom design.
The turnaround time between completing the design for a mask ROM and receiving the finished product is long, for the same reason. Mask ROM is impractical for R&D work since designers need to modify the contents of memory as they refine a design. If a product is shipped with faulty mask ROM, the only way to fix it is to recall the product and physically replace the ROM in every unit shipped. Subsequent developments have addressed these shortcomings. PROM, invented in 1956, allowed users to program its contents once by physically altering its structure with the application of high-voltage pulses; this addressed problems 1 and 2 above, since a company can order a large batch of fresh PROM chips and program them with the desired contents at its designers' convenience. The 1971 invention of EPROM solved problem 3, since EPROM can be reset to its unprogrammed state by exposure to strong ultraviolet light. EEPROM, invented in 1983, went a long way to solving problem 4, since an EEPROM can be programmed in-place if the containing device provides a means to receive the program contents from an external source.
Flash memory, invented at Toshiba in the mid-1980s, commercialized in the early 1990s, is a form of EEPROM that makes efficient use of chip area and can be erased and reprogrammed thousands of times without damage. 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. Rewriteable technologies were envisioned as replacements for mask ROM; the most recent development is NAND flash invented at Toshiba. Its designers explicitly broke from past practice, stating plainly that "the aim of NAND Flash is to replace hard disks," rather than the traditional use of ROM as a form of non-volatile primary storage; as of 2007, NAND has achieved this goal by offering throughput comparable to hard disks, higher tolerance of physical shock, extreme miniaturization, much lower power consumption. Every stored-program computer may use a form of non-volatile storage to store the initial program that runs when the computer is powered on or otherwise begins execution.
Every non-trivial computer needs some form of mutable memory to record changes in its state as it executes. Forms of read-only memory were employed as non-volatile storage for programs in most early stored-program computers, such as ENIAC after 1948. Read-only memory was simpler to implement since it needed only a mechanism to read stored values, not to change them in-place, thus could be implemented with crude electromechanical devices. 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.
Core rope memory
Core rope memory is a form of read-only memory for computers, first used in the 1960s by early NASA Mars space probes and in the Apollo Guidance Computer designed and programmed by the Massachusetts Institute of Technology Instrumentation Lab and built by Raytheon. Contrary to ordinary coincident-current magnetic-core memory, used for random access memory at the time, the ferrite cores in a core rope are just used as transformers; the signal from a word line wire passing through a given core is coupled to the bit line wire and interpreted as a binary "one", while a word line wire that bypasses the core is not coupled to the bit line wire and is read as a "zero". In the AGC, up to 64 wires could be passed through a single core. Software written by MIT programmers was woven into core rope memory by female workers in factories; some programmers nicknamed the finished product LOL memory, for Little Old Lady memory. By the standards of the time, a large amount of data could be stored in a small installed volume of core rope memory: 72 kilobytes per cubic foot, or 2.5 megabytes per cubic meter.
This was about 18 times the amount of data per volume compared to standard read-write core memory: the Block II Apollo Guidance Computer used 36,864 sixteen-bit words of core rope memory and 4,096 words of magnetic core memory. "Computer for Apollo" NASA/MIT film from 1965. Visual Introduction to the Apollo Guidance Computer, part 3: Manufacturing the Apollo Guidance Computer. – By Raytheon.
