Volt
The volt is the derived unit for electric potential, electric potential difference, electromotive force. It is named after the Italian physicist Alessandro Volta. One volt is defined as the difference in electric potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points, it is equal to the potential difference between two parallel, infinite planes spaced 1 meter apart that create an electric field of 1 newton per coulomb. Additionally, it is the potential difference between two points that will impart one joule of energy per coulomb of charge that passes through it, it can be expressed in terms of SI base units as V = potential energy charge = J C = kg ⋅ m 2 A ⋅ s 3. It can be expressed as amperes times ohms, watts per ampere, or joules per coulomb, equivalent to electronvolts per elementary charge: V = A ⋅ Ω = W A = J C = eV e; the "conventional" volt, V90, defined in 1987 by the 18th General Conference on Weights and Measures and in use from 1990, is implemented using the Josephson effect for exact frequency-to-voltage conversion, combined with the caesium frequency standard.
For the Josephson constant, KJ = 2e/h, the "conventional" value KJ-90 is used: K J-90 = 0.4835979 GHz μ V. This standard is realized using a series-connected array of several thousand or tens of thousands of junctions, excited by microwave signals between 10 and 80 GHz. Empirically, several experiments have shown that the method is independent of device design, measurement setup, etc. and no correction terms are required in a practical implementation. In the water-flow analogy, sometimes used to explain electric circuits by comparing them with water-filled pipes, voltage is likened to difference in water pressure. Current is proportional to the amount of water flowing at that pressure. A resistor would be a reduced diameter somewhere in the piping and a capacitor/inductor could be likened to a "U" shaped pipe where a higher water level on one side could store energy temporarily; the relationship between voltage and current is defined by Ohm's law. Ohm's Law is analogous to the Hagen–Poiseuille equation, as both are linear models relating flux and potential in their respective systems.
The voltage produced by each electrochemical cell in a battery is determined by the chemistry of that cell. See Galvanic cell § Cell voltage. Cells can be combined in series for multiples of that voltage, or additional circuitry added to adjust the voltage to a different level. Mechanical generators can be constructed to any voltage in a range of feasibility. Nominal voltages of familiar sources: Nerve cell resting potential: ~75 mV Single-cell, rechargeable NiMH or NiCd battery: 1.2 V Single-cell, non-rechargeable: alkaline battery: 1.5 V. Some antique vehicles use 6.3 volts. Electric vehicle battery: 400 V when charged Household mains electricity AC: 100 V in Japan 120 V in North America, 230 V in Europe, Asia and Australia Rapid transit third rail: 600–750 V High-speed train overhead power lines: 25 kV at 50 Hz, but see the List of railway electrification systems and 25 kV at 60 Hz for exceptions. High-voltage electric power transmission lines: 110 kV and up Lightning: Varies often around 100 MV.
In 1800, as the result of a professional disagreement over the galvanic response advocated by Luigi Galvani, Alessandro Volta developed the so-called voltaic pile, a forerunner of the battery, which produced a steady electric current. Volta had determined that the most effective pair of dissimilar metals to produce electricity was zinc and silver. In 1861, Latimer Clark and Sir Charles Bright coined the name "volt" for the unit of resistance. By 1873, the British Association for the Advancement of Science had defined the volt and farad. In 1881, the International Electrical Congress, now the International Electrotechnical Commission, approved the volt as the unit for electromotive force, they made the volt equal to 108 cgs units of voltage
Industry Standard Architecture
Industry Standard Architecture is the 16-bit internal bus of IBM PC/AT and similar computers based on the Intel 80286 and its immediate successors during the 1980s. The bus was backward compatible with the 8-bit bus of the 8088-based IBM PC, including the IBM PC/XT as well as IBM PC compatibles. Referred to as the PC/AT-bus, it was termed I/O Channel by IBM; the ISA term was coined as a retronym by competing PC-clone manufacturers in the late 1980s or early 1990s as a reaction to IBM attempts to replace the AT-bus with its new and incompatible Micro Channel architecture. The 16-bit ISA bus was used with 32-bit processors for several years. An attempt to extend it to 32 bits, called Extended Industry Standard Architecture, was not successful, however. Buses such as VESA Local Bus and PCI were used instead along with ISA slots on the same mainboard. Derivatives of the AT bus structure were and still are used in ATA/IDE, the PCMCIA standard, Compact Flash, the PC/104 bus, internally within Super I/O chips.
The ISA bus was developed by a team led by Mark Dean at IBM as part of the IBM PC project in 1981 Compaq created the term "Industry Standard Architecture" to replace "PC compatible". ISA originated as an 8-bit system. A 16-bit version, the IBM AT bus, was introduced with the release of the IBM PC/AT in 1984. In 1988, the 32-bit Extended Industry Standard Architecture standard was proposed by the "Gang of Nine" group of PC-compatible manufacturers that included Compaq. In the process, they retroactively renamed the AT bus to "ISA" to avoid infringing IBM's trademark on its PC/AT computer. IBM designed the 8-bit version as a buffered interface to the motherboard buses of the Intel 8088 CPU in the IBM PC and PC/XT; the 16-bit version was an upgrade for the motherboard buses of the Intel 80286 CPU used in the IBM AT. The ISA bus was therefore synchronous with the CPU clock, until sophisticated buffering methods were implemented by chipsets to interface ISA to much faster CPUs. ISA allows for bus mastering.
Only the first 16 MB of main memory is addressable. The original 8-bit bus ran from the 4.77 MHz clock of the 8088 CPU in the IBM PC and PC/XT. The original 16-bit bus ran from the CPU clock of the 80286 in IBM PC/AT computers, 6 MHz in the first models and 8 MHz in models; the IBM RT PC used the 16-bit bus. ISA was used in some non-IBM compatible machines such as Motorola 68k-based Apollo and Amiga 3000 workstations, the short-lived AT&T Hobbit and the PowerPC-based BeBox. Companies like Dell improved the AT bus's performance but in 1987, IBM replaced the AT bus with its proprietary Micro Channel Architecture. MCA overcame many of the limitations apparent in ISA but was an effort by IBM to regain control of the PC architecture and the PC market. MCA was far more advanced than ISA and had many features that would appear in PCI. However, MCA was a closed standard whereas IBM had released full specifications and circuit schematics for ISA. Computer manufacturers responded to MCA by developing the Extended Industry Standard Architecture and the VESA Local Bus.
VLB used some electronic parts intended for MCA because component manufacturers were equipped to manufacture them. Both EISA and VLB were backwards-compatible expansions of the AT bus. Users of ISA-based machines had to know special information about the hardware they were adding to the system. While a handful of devices were "plug-n-play", this was rare. Users had to configure parameters when adding a new device, such as the IRQ line, I/O address, or DMA channel. MCA had done away with this complication and PCI incorporated many of the ideas first explored with MCA, though it was more directly descended from EISA; this trouble with configuration led to the creation of ISA PnP, a plug-n-play system that used a combination of modifications to hardware, the system BIOS, operating system software to automatically manage resource allocations. In reality, ISA PnP could be troublesome and did not become well-supported until the architecture was in its final days. PCI slots were the first physically-incompatible expansion ports to directly squeeze ISA off the motherboard.
At first, motherboards were ISA, including a few PCI slots. By the mid-1990s, the two slot types were balanced, ISA slots soon were in the minority of consumer systems. Microsoft's PC 99 specification recommended that ISA slots be removed though the system architecture still required ISA to be present in some vestigial way internally to handle the floppy drive, serial ports, etc., why the software compatible LPC bus was created. ISA slots remained for a few more years, towards the turn of the century it was common to see systems with an Accelerated Graphics Port sitting near the central processing unit, an array of PCI slots, one or two ISA slots near the end. In late 2008 floppy disk drives and serial ports were disappearing, the extinction of vestigial ISA from chipsets was on the horizon. PCI slots are "rotated" compared to their ISA counterparts—PCI cards were inserted "upside-down," allowing ISA and PCI connectors to squeeze together on the motherboard. Only one of the two connectors can be used in each slot at a time, but this allowed for greater flexibility.
The AT Attachment hard disk interface is directly descended from the 16-bit ISA of the PC/AT. ATA has its origins in hardcards that integrated a hard disk drive and a hard disk controller onto one card; this was at best awkward and at worst damaging to the motherboard, as ISA slots were
CompactFlash
CompactFlash is a flash memory mass storage device used in portable electronic devices. The format was specified and the devices were first manufactured by SanDisk in 1994. CompactFlash became one of the most successful of the early memory card formats, surpassing Miniature Card and SmartMedia. Subsequent formats, such as MMC/SD, various Memory Stick formats, xD-Picture Card offered stiff competition. Most of these cards are smaller than CompactFlash while offering comparable capacity and speed. Proprietary memory card formats for use in professional audio and video, such as P2 and SxS, are faster, but physically larger and more costly. CompactFlash remains popular and is supported by many professional devices and high-end consumer devices; as of 2017, both Canon and Nikon use CompactFlash for their flagship digital still cameras. Canon chose CompactFlash as the recording medium for its professional high-definition tapeless video cameras. Ikegami professional video cameras can record digital video onto CompactFlash cards through an adaptor.
Traditional CompactFlash cards use the Parallel ATA interface, but in 2008, a variant of CompactFlash, CFast was announced. CFast is based on the Serial ATA interface. In November 2010, SanDisk and Nikon presented a next generation card format to the CompactFlash Association; the new format has a similar form factor to CF/CFast but is based on the PCI Express interface instead of Parallel ATA or Serial ATA. With potential read and write speeds of 1 Gbit/s and storage capabilities beyond 2 TiB, the new format is aimed at high-definition camcorders and high-resolution digital cameras, but the new cards are not backward compatible with either CompactFlash or CFast; the XQD card format was announced by the CompactFlash Association in December 2011. There are two main subdivisions of CF cards, 3.3 mm-thick type I and 5 mm-thick type II. The type II slot is used by miniature hard drives and some other devices, such as the Hasselblad CFV Digital Back for the Hasselblad series of medium format cameras.
There are four main card speeds: original CF, CF High Speed, faster CF 3.0 standard and the faster CF 4.0 standard adopted as of 2007. CompactFlash was built around Intel's NOR-based flash memory, but has switched to NAND technology. CF is among the oldest and most successful formats, has held a niche in the professional camera market well, it has benefited from both a better cost to memory-size ratio and, for much of the format's life greater available capacity than other formats. CF cards can be used directly in a PC Card slot with a plug adapter, used as an ATA or PCMCIA storage device with a passive adapter or with a reader, or attached to other types of ports such as USB or FireWire; as some newer card types are smaller, they can be used directly in a CF card slot with an adapter. Formats that can be used this way include SD/MMC, Memory Stick Duo, xD-Picture Card in a Type I slot and SmartMedia in a Type II slot, as of 2005; some multi-card readers use CF for I/O as well. The CompactFlash interface is a 50-pin subset of the 68-pin PCMCIA connector.
"It can be slipped into a passive 68-pin PCMCIA Type II to CF Type I adapter that meets PCMCIA electrical and mechanical interface specifications", according to compactflash.org. The interface operates, depending on the state of a mode pin on power-up, as either a 16-bit PC Card or as an IDE interface. Unlike the PC Card interface, no dedicated programming voltages are provided on the CompactFlash interface. CompactFlash IDE mode defines an interface, smaller than, but electrically identical to, the ATA interface; the CF device appears to the host device as if it were a hard disk. CF devices operate at 3.3 volts or 5 volts, can be swapped from system to system. CompactFlash supports 28-bit logical block addressing. CF cards with flash memory are able to cope with rapid changes in temperature. Industrial versions of flash memory cards can operate at a range of −45 °C to +85 °C. NOR-based flash has lower density than newer NAND-based systems, CompactFlash is therefore the physically largest of the three memory card formats introduced in the early 1990s, being derived from the JEIDA/PCMCIA Memory Card formats.
The other two are Miniature SmartMedia. However, CF did switch to NAND type memory later; the IBM Microdrive format made by Hitachi, implements the CF Type II interface, but is a hard disk drive as opposed to solid-state memory. Seagate made CF HDDs. CompactFlash IDE emulation speed is specified in "x" ratings, e.g. 8x, 20x, 133x. This is the same system used for CD-ROMs and indicates the maximum transfer rate in the form of a multiplier based on the original audio CD data transfer rate, 150 kB/s. R = K ⋅ 150 kB/s where R = transfer rate, K = speed rating. For example, 133x rating means transfer speed of: 133 × 150 kB/s ≈ 20 MB/s; these are manufacturer speed ratings. Actual transfer speed may be lower, than shown on the card depending on several factors; the speed rating quoted is always the read speed, while write speed is slower. For reads, the onboard controller first powers up the memory chips from standby. Reads are in parallel, error correction is done on the data transferred through the interface 16 bits at a time.
Error checking is required due to soft read errors. Writes require powerup from standby, wear leveling calculation, a block erase of the area to be written to, E
USB
USB is an industry standard that establishes specifications for cables and protocols for connection and power supply between personal computers and their peripheral devices. Released in 1996, the USB standard is maintained by the USB Implementers Forum. There have been three generations of USB specifications: USB 2.0 and USB 3.x. USB was designed to standardize the connection of peripherals like keyboards, pointing devices, digital still and video cameras, portable media players, disk drives and network adapters to personal computers, both to communicate and to supply electric power, it has replaced interfaces such as serial ports and parallel ports, has become commonplace on a wide range of devices. USB connectors have been replacing other types for battery chargers of portable devices; this section is intended to allow fast identification of USB receptacles on equipment. Further diagrams and discussion of plugs and receptacles can be found in the main article above; the Universal Serial Bus was developed to simplify and improve the interface between personal computers and peripheral devices, when compared with existing standard or ad-hoc proprietary interfaces.
From the computer user's perspective, the USB interface improved ease of use in several ways. The USB interface is self-configuring, so the user need not adjust settings on the device and interface for speed or data format, or configure interrupts, input/output addresses, or direct memory access channels. USB connectors are standardized at the host, so any peripheral can use any available receptacle. USB takes full advantage of the additional processing power that can be economically put into peripheral devices so that they can manage themselves; the USB interface is "hot pluggable", meaning devices can be exchanged without rebooting the host computer. Small devices can be powered directly from displacing extra power supply cables; because use of the USB logos is only permitted after compliance testing, the user can have confidence that a USB device will work as expected without extensive interaction with settings and configuration. Installation of a device relying on the USB standard requires minimal operator action.
When a device is plugged into a port on a running personal computer system, it is either automatically configured using existing device drivers, or the system prompts the user to locate a driver, installed and configured automatically. For hardware manufacturers and software developers, the USB standard eliminates the requirement to develop proprietary interfaces to new peripherals; the wide range of transfer speeds available from a USB interface suits devices ranging from keyboards and mice up to streaming video interfaces. A USB interface can be designed to provide the best available latency for time-critical functions, or can be set up to do background transfers of bulk data with little impact on system resources; the USB interface is generalized with no signal lines dedicated to only one function of one device. USB cables are limited in length, as the standard was meant to connect to peripherals on the same table-top, not between rooms or between buildings. However, a USB port can be connected to a gateway.
USB has "master-slave" protocol for addressing peripheral devices. Some extension to this limitation is possible through USB On-The-Go. A host cannot "broadcast" signals to all peripherals at once, each must be addressed individually; some high speed peripheral devices require sustained speeds not available in the USB standard. While converters exist between certain "legacy" interfaces and USB, they may not provide full implementation of the legacy hardware. For a product developer, use of USB requires implementation of a complex protocol and implies an "intelligent" controller in the peripheral device. Developers of USB devices intended for public sale must obtain a USB ID which requires a fee paid to the Implementers' Forum. Developers of products that use the USB specification must sign an agreement with Implementer's Forum. Use of the USB logos on the product require annual fees and membership in the organization. A group of seven companies began the development of USB in 1994: Compaq, DEC, IBM, Microsoft, NEC, Nortel.
The goal was to make it fundamentally easier to connect external devices to PCs by replacing the multitude of connectors at the back of PCs, addressing the usability issues of existing interfaces, simplifying software configuration of all devices connected to USB, as well as permitting greater data rates for external devices. Ajay Bhatt and his team worked on the standard at Intel; the original USB 1.0 specification, introduced in January 1996, defined data transfer rates of 1.5 Mbit/s Low Speed and 12 Mbit/s Full Speed. Microsoft Windows 95, OSR 2.1 provided OEM support for the devices. The first used version of USB was 1.1, released in September 1998. The 12 Mbit/s data rate was intended for higher-speed devices such as disk drives, the lower 1.5 Mbit/s rate for low data
Memory card
A memory card, flash card or memory cartridge is an electronic flash memory data storage device used for storing digital information. These are used in portable electronic devices, such as digital cameras, mobile phones, laptop computers, tablets, PDAs, portable media players, video game consoles, electronic keyboards, digital pianos. PC Cards were the first commercial memory card formats to come out, but are now used in industrial applications and to connect I/O devices such as modems. Since 1994, a number of memory card formats smaller than the PC Card arrived, the first one was CompactFlash and SmartMedia and Miniature Card; the desire for smaller cards for cell-phones, PDAs, compact digital cameras drove a trend that left the previous generation of "compact" cards looking big. In digital cameras SmartMedia and CompactFlash had been successful. In 2001, SM alone captured 50% of the digital camera market and CF had captured the professional digital camera market. By 2005 however, SD/MMC had nearly taken over SmartMedia's spot, though not to the same level and with stiff competition coming from Memory Stick variants, as well CompactFlash.
In industrial and embedded fields the venerable PC card memory cards still manage to maintain a niche, while in mobile phones and PDAs, the memory card has become smaller. Since 2010, new products of Sony and Olympus have been offered with an additional SD-Card slot; the format war has turned in SD-Card's favor. PCMCIA ATA Type I Card PCMCIA Type II, Type III cards CompactFlash Card, CompactFlash High-Speed CompactFlash Type II, CF+, CF3.0 Microdrive CFexpress MiniCard SmartMedia Card xD-Picture Card, xD-Picture Card Type M Memory Stick, MagicGate Memory Stick. MU-Flash C-Flash SIM card Smart card UFC FISH Universal Transportable Memory Card Standard Intelligent Stick SxS memory card, a new memory card specification developed by Sandisk and Sony. SxS complies to the ExpressCard industry standard. Nexflash Winbond Serial Flash Module cards, size range 2 mb and 4 mb. Many older video game consoles used memory cards to hold saved game data. Cartridge-based systems used battery-backed volatile RAM within each individual cartridge to hold saves for that game.
Cartridges without this RAM wouldn't save progress at all. The Neo Geo AES, released in 1990 by SNK, was the first video game console able to use a memory card. AES memory cards were compatible with Neo-Geo MVS arcade cabinets, allowing players to migrate saves between home and arcade systems and vice versa. Memory cards became commonplace when home consoles moved to read-only optical discs for storing the game program, beginning with systems such as the TurboGrafx-CD and Sega-CD; until the sixth generation of video game consoles, memory cards were based on proprietary formats. Home consoles now use hard disk drive storage for saved games and allow the use of generic USB flash drives or other card formats via a memory card reader to transport game saves and other game information, along with cloud storage saving, though most portable gaming systems still rely on custom memory cartridges to store program data, due to their low power consumption, smaller physical size and reduced mechanical complexity.
Comparison of memory cards Hot swapping
Wi-Fi
Wi-Fi is technology for radio wireless local area networking of devices based on the IEEE 802.11 standards. Wi‑Fi is a trademark of the Wi-Fi Alliance, which restricts the use of the term Wi-Fi Certified to products that complete after many years of testing the 802.11 committee interoperability certification testing. Devices that can use Wi-Fi technologies include, among others and laptops, video game consoles and tablets, smart TVs, digital audio players, digital cameras and drones. Wi-Fi compatible devices can connect to the Internet via a wireless access point; such an access point has a range of about 20 meters indoors and a greater range outdoors. Hotspot coverage can be as small as a single room with walls that block radio waves, or as large as many square kilometres achieved by using multiple overlapping access points. Different versions of Wi-Fi exist, with radio bands and speeds. Wi-Fi most uses the 2.4 gigahertz UHF and 5 gigahertz SHF ISM radio bands. Each channel can be time-shared by multiple networks.
These wavelengths work best for line-of-sight. Many common materials absorb or reflect them, which further restricts range, but can tend to help minimise interference between different networks in crowded environments. At close range, some versions of Wi-Fi, running on suitable hardware, can achieve speeds of over 1 Gbit/s. Anyone within range with a wireless network interface controller can attempt to access a network. Wi-Fi Protected Access is a family of technologies created to protect information moving across Wi-Fi networks and includes solutions for personal and enterprise networks. Security features of WPA have included stronger protections and new security practices as the security landscape has changed over time. In 1971, ALOHAnet connected the Hawaiian Islands with a UHF wireless packet network. ALOHAnet and the ALOHA protocol were early forerunners to Ethernet, the IEEE 802.11 protocols, respectively. A 1985 ruling by the U. S. Federal Communications Commission released the ISM band for unlicensed use.
These frequency bands are the same ones used by equipment such as microwave ovens and are subject to interference. In 1991, NCR Corporation with AT&T Corporation invented the precursor to 802.11, intended for use in cashier systems, under the name WaveLAN. The Australian radio-astronomer Dr John O'Sullivan with his colleagues Terence Percival, Graham Daniels, Diet Ostry, John Deane developed a key patent used in Wi-Fi as a by-product of a Commonwealth Scientific and Industrial Research Organisation research project, "a failed experiment to detect exploding mini black holes the size of an atomic particle". Dr O'Sullivan and his colleagues are credited with inventing Wi-Fi. In 1992 and 1996, CSIRO obtained patents for a method used in Wi-Fi to "unsmear" the signal; the first version of the 802.11 protocol was released in 1997, provided up to 2 Mbit/s link speeds. This was updated in 1999 with 802.11b to permit 11 Mbit/s link speeds, this proved to be popular. In 1999, the Wi-Fi Alliance formed as a trade association to hold the Wi-Fi trademark under which most products are sold.
Wi-Fi uses a large number of patents held by many different organizations. In April 2009, 14 technology companies agreed to pay CSIRO $1 billion for infringements on CSIRO patents; this led to Australia labeling Wi-Fi as an Australian invention, though this has been the subject of some controversy. CSIRO won a further $220 million settlement for Wi-Fi patent-infringements in 2012 with global firms in the United States required to pay the CSIRO licensing rights estimated to be worth an additional $1 billion in royalties. In 2016, the wireless local area network Test Bed was chosen as Australia's contribution to the exhibition A History of the World in 100 Objects held in the National Museum of Australia; the name Wi-Fi, commercially used at least as early as August 1999, was coined by the brand-consulting firm Interbrand. The Wi-Fi Alliance had hired Interbrand to create a name, "a little catchier than'IEEE 802.11b Direct Sequence'." Phil Belanger, a founding member of the Wi-Fi Alliance who presided over the selection of the name "Wi-Fi", has stated that Interbrand invented Wi-Fi as a pun on the word hi-fi, a term for high-quality audio technology.
Interbrand created the Wi-Fi logo. The yin-yang Wi-Fi logo indicates the certification of a product for interoperability; the Wi-Fi Alliance used the advertising slogan "The Standard for Wireless Fidelity" for a short time after the brand name was created. While inspired by the term hi-fi, the name was never "Wireless Fidelity"; the Wi-Fi Alliance was called the "Wireless Fidelity Alliance Inc" in some publications. Non-Wi-Fi technologies intended for fixed points, such as Motorola Canopy, are described as fixed wireless. Alternative wireless technologies include mobile phone standards, such as 2G, 3G, 4G, LTE; the name is sometimes written as WiFi, Wifi, or wifi, but these are not approved by the Wi-Fi Alliance. IEEE is a separate, but related organization and their website has stated "WiFi is a short name for Wireless Fidelity". To connect to a Wi-Fi LAN, a computer has to be equipped with a wireless network interface controller; the combination of computer and interface controllers is called a station.
A service set is the set of all the devices associated with a particular Wi-Fi network. The service set can be local, extended or mesh; each service set has an associated identifier, the 32-byte Service Set Identifier, which identifies the partic
Static random-access memory
Static random-access memory is a type of semiconductor memory that uses bistable latching circuitry to store each bit. SRAM exhibits data remanence, but it is still volatile in the conventional sense that data is lost when the memory is not powered; the term static differentiates SRAM from DRAM. SRAM is faster and more expensive than DRAM. Advantages: Simplicity – a refresh circuit is not needed Performance Reliability Low idle power consumptionDisadvantages: Price Density High operational power consumption The power consumption of SRAM varies depending on how it is accessed. On the other hand, static RAM used at a somewhat slower pace, such as in applications with moderately clocked microprocessors, draws little power and can have a nearly negligible power consumption when sitting idle – in the region of a few micro-watts. Several techniques have been proposed to manage power consumption of SRAM-based memory structures. General purpose products with asynchronous interface, such as the ubiquitous 28-pin 8K × 8 and 32K × 8 chips, as well as similar products up to 16 Mbit per chip with synchronous interface used for caches and other applications requiring burst transfers, up to 18 Mbit per chip integrated on chip as RAM or cache memory in micro-controllers as the primary caches in powerful microprocessors, such as the x86 family, many others to store the registers and parts of the state-machines used in some microprocessors on application specific ICs, or ASICs in Field Programmable Gate Array and Complex Programmable Logic Device Many categories of industrial and scientific subsystems, automotive electronics, similar, contain static RAM.
Some amount is embedded in all modern appliances, etc. that implement an electronic user interface. Several megabytes may be used in complex products such as digital cameras, cell phones, etc. SRAM in its dual-ported form is sometimes used for realtime digital signal processing circuits. SRAM is used in personal computers, workstations and peripheral equipment: CPU register files, internal CPU caches and external burst mode SRAM caches, hard disk buffers, router buffers, etc. LCD screens and printers normally employ static RAM to hold the image displayed. Static RAM was used for the main memory of some early personal computers such as the ZX80, TRS-80 Model 100 and Commodore VIC-20. Hobbyists home-built processor enthusiasts prefer SRAM due to the ease of interfacing, it is much easier to work with than DRAM as there are no refresh cycles and the address and data buses are directly accessible rather than multiplexed. In addition to buses and power connections, SRAM requires only three controls: Chip Enable, Write Enable and Output Enable.
In synchronous SRAM, Clock is included. Non-volatile SRAMs, or nvSRAMs, have standard SRAM functionality, but they save the data when the power supply is lost, ensuring preservation of critical information. NvSRAMs are used in a wide range of situations – networking and medical, among many others – where the preservation of data is critical and where batteries are impractical. PSRAMs have a DRAM storage core, combined with a self refresh circuit, they appear externally as a slower SRAM. They have a density/cost advantage over true SRAM, without the access complexity of DRAM. Bipolar junction transistor – fast but consumes a lot of power MOSFET – low power and common today Asynchronous – independent of clock frequency. Address, data in and other control signals are associated with the clock signalsIn 1990s, asynchronous SRAM used to be employed for fast access time. Asynchronous SRAM was used as main memory for small cache-less embedded processors used in everything from industrial electronics and measurement systems to hard disks and networking equipment, among many other applications.
Nowadays, synchronous SRAM is rather employed like Synchronous DRAM – DDR SDRAM memory is rather used than asynchronous DRAM. Synchronous memory interface is much faster as access time can be reduced by employing pipeline architecture. Furthermore, as DRAM is much cheaper than SRAM, SRAM is replaced by DRAM in the case when large volume of data is required. SRAM memory is however much faster for random access. Therefore, SRAM memory is used for CPU cache, small on-chip memory, FIFOs or other small buffers. Zero bus turnaround – the turnaround is the number of clock cycles it takes to change access to the SRAM from write to read and vice versa; the turnaround for ZBT SRAMs or the latency between read and write cycle is zero. SyncBurst – features synchronous burst write access to the SRAM to increase write operation to the SRAM DDR SRAM – Synchronous, single read/write port, double data rate I/O Quad Data Rate SRAM – Synchronous, separate read and write ports, quadruple data rate I/O Binary SRAM Ternary SRAM A typical SRAM cell is mad
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