Dynamic random-access memory
Dynamic random-access memory is a type of random access semiconductor memory that stores each bit of data in a separate tiny capacitor within an integrated circuit. The capacitor can either be discharged; the electric charge on the capacitors leaks off, so without intervention the data on the chip would soon be lost. To prevent this, DRAM requires an external memory refresh circuit which periodically rewrites the data in the capacitors, restoring them to their original charge; this refresh process is the defining characteristic of dynamic random-access memory, in contrast to static random-access memory which does not require data to be refreshed. Unlike flash memory, DRAM is volatile memory, since it loses its data when power is removed. However, DRAM does exhibit limited data remanence. DRAM is used in digital electronics where low-cost and high-capacity memory is required. One of the largest applications for DRAM is the main memory in modern graphics cards, it is used in many portable devices and video game consoles.
In contrast, SRAM, faster and more expensive than DRAM, is used where speed is of greater concern than cost and size, such as the cache memories in processors. Due to its need of a system to perform refreshing, DRAM has more complicated circuitry and timing requirements than SRAM, but it is much more used; the advantage of DRAM is the structural simplicity of its memory cells: only one transistor and a capacitor are required per bit, compared to four or six transistors in SRAM. This allows DRAM to reach high densities, making DRAM much cheaper per bit; the transistors and capacitors used are small. Due to the dynamic nature of its memory cells, DRAM consumes large amounts of power, with different ways for managing the power consumption. DRAM had a 47% increase in the price-per-bit in 2017, the largest jump in 30 years since the 45% percent jump in 1988, while in recent years the price has been going down; the cryptanalytic machine code-named "Aquarius" used at Bletchley Park during World War II incorporated a hard-wired dynamic memory.
Paper tape was read and the characters on it "were remembered in a dynamic store.... The store used a large bank of capacitors, which were either charged or not, a charged capacitor representing cross and an uncharged capacitor dot. Since the charge leaked away, a periodic pulse was applied to top up those still charged". In 1964, Arnold Farber and Eugene Schlig, working for IBM, created a hard-wired memory cell, using a transistor gate and tunnel diode latch, they replaced the latch with two transistors and two resistors, a configuration that became known as the Farber-Schlig cell. In 1965, Benjamin Agusta and his team at IBM created a 16-bit silicon memory chip based on the Farber-Schlig cell, with 80 transistors, 64 resistors, 4 diodes. In 1966, DRAM was invented by Dr. Robert Dennard at the IBM Thomas J. Watson Research Center, he was granted U. S. patent number 3,387,286 in 1968. Capacitors had been used for earlier memory schemes such as the drum of the Atanasoff–Berry Computer, the Williams tube and the Selectron tube.
The Toshiba "Toscal" BC-1411 electronic calculator, introduced in November 1966, used a form of DRAM built from discrete components. The first DRAM was introduced in 1969 by Advanced Memory system, Inc of Sunnyvale, CA; this 1000 bit chip was sold to Honeywell, Wang Computer, others. In 1969 Honeywell asked Intel to make a DRAM using a three-transistor cell; this became the Intel 1102 in early 1970. However, the 1102 had many problems, prompting Intel to begin work on their own improved design, in secrecy to avoid conflict with Honeywell; this became the first commercially available DRAM, the Intel 1103, in October 1970, despite initial problems with low yield until the fifth revision of the masks. The 1103 was laid out by Pat Earhart; the masks were cut by Judy Garcia. The first DRAM with multiplexed row and column address lines was the Mostek MK4096 4 Kbit DRAM designed by Robert Proebsting and introduced in 1973; this addressing scheme uses the same address pins to receive the low half and the high half of the address of the memory cell being referenced, switching between the two halves on alternating bus cycles.
This was a radical advance halving the number of address lines required, which enabled it to fit into packages with fewer pins, a cost advantage that grew with every jump in memory size. The MK4096 proved to be a robust design for customer applications. At the 16 Kbit density, the cost advantage increased. However, as density increased to 64 Kbit in the early 1980s, Mostek and other US manufacturers were overtaken by Japanese DRAM manufacturers dumping DRAMs on the US market. DRAM is arranged in a rectangular array of charge storage cells consisting of one capacitor and transistor per data bit; the figure to the right shows a simple example with a four-by-four cell matrix. Some DRAM matrices are many thousands of cells in width; the long horizontal lines connecting each row are known as word-lines. Each column of cells is composed of two bit-lines, each connected to every other storage cell in the column, they are known as the "+" and "−" bit lines. A sense amplifier is essent
In physics refraction is the change in direction of a wave passing from one medium to another or from a gradual change in the medium. Refraction of light is the most observed phenomenon, but other waves such as sound waves and water waves experience refraction. How much a wave is refracted is determined by the change in wave speed and the initial direction of wave propagation relative to the direction of change in speed. For light, refraction follows Snell's law, which states that, for a given pair of media, the ratio of the sines of the angle of incidence θ1 and angle of refraction θ2 is equal to the ratio of phase velocities in the two media, or equivalently, to the indices of refraction of the two media. Sin θ 1 sin θ 2 = v 1 v 2 = n 2 n 1 Optical prisms and lenses utilize refraction to redirect light, as does the human eye; the refractive index of materials varies with the wavelength of light, thus the angle of the refraction varies correspondingly. This is called dispersion and causes prisms and rainbows to divide white light into its constituent spectral colors.
Consider a wave going from one material to another where its speed is slower as in the figure. If it reaches the interface between the materials at an angle one side of the wave will reach the second material first, therefore slow down earlier. With one side of the wave going slower the whole wave will pivot towards that side; this is why a wave will bend away from the surface or toward the normal when going into a slower material. In the opposite case of a wave reaching a material where the speed is higher, one side of the wave will speed up and the wave will pivot away from that side. Another way of understanding the same thing is to consider the change in wavelength at the interface; when the wave goes from one material to another where the wave has a different speed v, the frequency f of the wave will stay the same, but the distance between wavefronts or wavelength λ=v/f will change. If the speed is decreased, such as in the figure to the right, the wavelength will decrease. With an angle between the wave fronts and the interface and change in distance between the wave fronts the angle must change over the interface to keep the wave fronts intact.
From these considerations the relationship between the angle of incidence θ1, angle of transmission θ2 and the wave speeds v1 and v2 in the two materials can be derived. This is the law of refraction or Snell's law and can be written as sin θ 1 sin θ 2 = v 1 v 2; the phenomenon of refraction can in a more fundamental way be derived from the 2 or 3-dimensional wave equation. The boundary condition at the interface will require the tangential component of the wave vector to be identical on the two sides of the interface. Since the magnitude of the wave vector depend on the wave speed this requires a change in direction of the wave vector; the relevant wave speed in the discussion above is the phase velocity of the wave. This is close to the group velocity which can be seen as the truer speed of a wave, but when they differ it is important to use the phase velocity in all calculations relating to refraction. A wave traveling perpendicular to a boundary, i.e. having its wavefronts parallel to the boundary, will not change direction if the speed of the wave changes.
Refraction of light can be seen in many places in our everyday life. It makes objects under a water surface appear closer than they are, it is what optical lenses are based on, allowing for instruments such as glasses, binoculars and the human eye. Refraction is responsible for some natural optical phenomena including rainbows and mirages. For light, the refractive index n of a material is more used than the wave phase speed v in the material, they are, directly related through the speed of light in vacuum c as n = c v. In optics, the law of refraction is written as n 1 sin θ 1 = n 2 sin θ 2. Refraction occurs when light goes through a water surface since water has a refractive index of 1.33 and air has a refractive index of about 1. Looking at a straight object, such as a pencil in the figure here, placed at a slant in the water, the object appears to bend at the water's surface; this is due to the bending of light rays. Once the rays reach the eye, the eye traces them back as straight lines.
The lines of sight intersect at a higher position than. This causes the pencil to appear higher and the water to appear shallower than it is; the depth that the water appears to be when viewed from above is known as the apparent depth. This is an important consideration for spearfishing from the surface because it will make the target fish appear to be in a different place, the fisher must aim lower to catch the fish. Conversely
Sonar is a technique that uses sound propagation to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. Two types of technology share the name "sonar": passive sonar is listening for the sound made by vessels. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of radar. Sonar may be used in air for robot navigation, SODAR is used for atmospheric investigations; the term sonar is used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from low to high; the study of underwater sound is known as underwater hydroacoustics. The first recorded use of the technique was by Leonardo da Vinci in 1490 who used a tube inserted into the water to detect vessels by ear, it was developed during World War I to counter the growing threat of submarine warfare, with an operational passive sonar system in use by 1918.
Modern active sonar systems use an acoustic transponder to generate a sound wave, reflected back from target objects. Although some animals have used sound for communication and object detection for millions of years, use by humans in the water is recorded by Leonardo da Vinci in 1490: a tube inserted into the water was said to be used to detect vessels by placing an ear to the tube. In the late 19th century an underwater bell was used as an ancillary to lighthouses or light ships to provide warning of hazards; the use of sound to "echo-locate" underwater in the same way as bats use sound for aerial navigation seems to have been prompted by the Titanic disaster of 1912. The world's first patent for an underwater echo-ranging device was filed at the British Patent Office by English meteorologist Lewis Fry Richardson a month after the sinking of the Titanic, a German physicist Alexander Behm obtained a patent for an echo sounder in 1913; the Canadian engineer Reginald Fessenden, while working for the Submarine Signal Company in Boston, built an experimental system beginning in 1912, a system tested in Boston Harbor, in 1914 from the U.
S. Revenue Cutter Miami on the Grand Banks off Newfoundland. In that test, Fessenden echo ranging; the "Fessenden oscillator", operated at about 500 Hz frequency, was unable to determine the bearing of the iceberg due to the 3-metre wavelength and the small dimension of the transducer's radiating face. The ten Montreal-built British H-class submarines launched in 1915 were equipped with Fessenden oscillators. During World War I the need to detect; the British made early use of underwater listening devices called hydrophones, while the French physicist Paul Langevin, working with a Russian immigrant electrical engineer Constantin Chilowsky, worked on the development of active sound devices for detecting submarines in 1915. Although piezoelectric and magnetostrictive transducers superseded the electrostatic transducers they used, this work influenced future designs. Lightweight sound-sensitive plastic film and fibre optics have been used for hydrophones, while Terfenol-D and PMN have been developed for projectors.
In 1916, under the British Board of Invention and Research, Canadian physicist Robert William Boyle took on the active sound detection project with A. B. Wood, producing a prototype for testing in mid-1917; this work, for the Anti-Submarine Division of the British Naval Staff, was undertaken in utmost secrecy, used quartz piezoelectric crystals to produce the world's first practical underwater active sound detection apparatus. To maintain secrecy, no mention of sound experimentation or quartz was made – the word used to describe the early work was changed to "ASD"ics, the quartz material to "ASD"ivite: "ASD" for "Anti-Submarine Division", hence the British acronym ASDIC. In 1939, in response to a question from the Oxford English Dictionary, the Admiralty made up the story that it stood for "Allied Submarine Detection Investigation Committee", this is still believed, though no committee bearing this name has been found in the Admiralty archives. By 1918, Britain and France had built prototype active systems.
The British tested their ASDIC on HMS Antrim in 1920 and started production in 1922. The 6th Destroyer Flotilla had ASDIC-equipped vessels in 1923. An anti-submarine school HMS Osprey and a training flotilla of four vessels were established on Portland in 1924; the U. S. Sonar QB set arrived in 1931. By the outbreak of World War II, the Royal Navy had five sets for different surface ship classes, others for submarines, incorporated into a complete anti-submarine attack system; the effectiveness of early ASDIC was hampered by the use of the depth charge as an anti-submarine weapon. This required an attacking vessel to pass over a submerged contact before dropping charges over the stern, resulting in a loss of ASDIC contact in the moments leading up to attack; the hunter was firing blind, during which time a submarine commander could take evasive action. This situation was remedied by using several ships cooperating and by the adoption of "ahead-throwing weapons", such as Hedgehogs and Squids, which proj
Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, spacecraft, guided missiles, motor vehicles, weather formations, terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the object. Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed. Radar was developed secretly for military use by several nations in the period before and during World War II. A key development was the cavity magnetron in the UK, which allowed the creation of small systems with sub-meter resolution; the term RADAR was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging The term radar has since entered English and other languages as a common noun, losing all capitalization.
The modern uses of radar are diverse, including air and terrestrial traffic control, radar astronomy, air-defense systems, antimissile systems, marine radars to locate landmarks and other ships, aircraft anticollision systems, ocean surveillance systems, outer space surveillance and rendezvous systems, meteorological precipitation monitoring and flight control systems, guided missile target locating systems, ground-penetrating radar for geological observations, range-controlled radar for public health surveillance. High tech radar systems are associated with digital signal processing, machine learning and are capable of extracting useful information from high noise levels. Radar is a key technology that the self-driving systems are designed to use, along with sonar and other sensors. Other systems similar to radar make use of other parts of the electromagnetic spectrum. One example is "lidar". With the emergence of driverless vehicles, Radar is expected to assist the automated platform to monitor its environment, thus preventing unwanted incidents.
As early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects. In 1895, Alexander Popov, a physics instructor at the Imperial Russian Navy school in Kronstadt, developed an apparatus using a coherer tube for detecting distant lightning strikes; the next year, he added a spark-gap transmitter. In 1897, while testing this equipment for communicating between two ships in the Baltic Sea, he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, but he did nothing more with this observation; the German inventor Christian Hülsmeyer was the first to use radio waves to detect "the presence of distant metallic objects". In 1904, he demonstrated the feasibility of detecting a ship in dense fog, but not its distance from the transmitter, he obtained a patent for his detection device in April 1904 and a patent for a related amendment for estimating the distance to the ship.
He got a British patent on September 23, 1904 for a full radar system, that he called a telemobiloscope. It operated on a 50 cm wavelength and the pulsed radar signal was created via a spark-gap, his system used the classic antenna setup of horn antenna with parabolic reflector and was presented to German military officials in practical tests in Cologne and Rotterdam harbour but was rejected. In 1915, Robert Watson-Watt used radio technology to provide advance warning to airmen and during the 1920s went on to lead the U. K. research establishment to make many advances using radio techniques, including the probing of the ionosphere and the detection of lightning at long distances. Through his lightning experiments, Watson-Watt became an expert on the use of radio direction finding before turning his inquiry to shortwave transmission. Requiring a suitable receiver for such studies, he told the "new boy" Arnold Frederic Wilkins to conduct an extensive review of available shortwave units. Wilkins would select a General Post Office model after noting its manual's description of a "fading" effect when aircraft flew overhead.
Across the Atlantic in 1922, after placing a transmitter and receiver on opposite sides of the Potomac River, U. S. Navy researchers A. Hoyt Taylor and Leo C. Young discovered that ships passing through the beam path caused the received signal to fade in and out. Taylor submitted a report, suggesting that this phenomenon might be used to detect the presence of ships in low visibility, but the Navy did not continue the work. Eight years Lawrence A. Hyland at the Naval Research Laboratory observed similar fading effects from passing aircraft. Before the Second World War, researchers in the United Kingdom, Germany, Japan, the Netherlands, the Soviet Union, the United States, independently and in great secrecy, developed technologies that led to the modern version of radar. Australia, New Zealand, South Africa followed prewar Great Britain's radar development, Hungary generated its radar technology during the war. In France in 1934, following systematic studies on the split-anode magnetron, the research branch of the Compagnie Générale de Télégraphie Sans Fil headed by Maurice Ponte with Henri Gutton, Sylvain Berline and M. Hugon, began developing an obstacle-locatin
The Cromemco Cyclops, introduced in 1975 by Cromemco, was the first commercial all-digital camera using a digital MOS area image sensor. It was the first digital camera to be interfaced to a microcomputer; the digital sensor for the camera was a modified 1K memory chip that offered a resolution of 32 × 32 pixels. The Cyclops Camera was developed by Terry Walker, Harry Garland, Roger Melen, introduced as a hobbyist construction project in the February 1975 issue of Popular Electronics magazine. One month earlier the MITS Altair 8800 microcomputer had been introduced in this same magazine. Les Solomon, technical editor of Popular Electronics, saw the value of interfacing the Cyclops to the Altair, put Roger Melen in contact with Ed Roberts to discuss a collaboration. Roger Melen met with Ed Roberts at MITS headquarters in New Mexico. Roberts encouraged Melen to interface the Cyclops to the Altair, promising to ship Melen an early Altair computer so that he and his colleagues could begin work on this project.
Roger Melen formed a partnership with Harry Garland to produce the Cyclops Camera, other products for the Altair computer. They named their new venture "Cromemco" after the Stanford University dormitory where they both had lived as graduate students. In January 1976 MITS introduced the Cromemco Cyclops Camera as the first peripheral for the Altair Computer; the Cyclops Camera used an innovative image sensor, a modified MOS computer memory chip. The opaque cover on the chip was replaced with a glass lid; the theory of operation was described in the original Popular Electronics article. The 1024 memory locations, which were arranged in a 32 × 32 array, were filled with all 1s. Light shining on these memory cells would cause their contents to change to 0s; the stronger the light, the more a cell would change from 1 to 0. The Cyclops used a 25mm f2.8 D-mount lens to focus an image on the sensor array. The memory array was scanned once to store all 1’s in the memory elements; this was followed by a series of 15 read-out scans.
The cells that had the most incident light changed from 1 to 0 the soonest. Cells with little or no incident light would not change at all. So with a series of scans the Cyclops could produce a digital, gray-scale representation of the image; the Cyclops had two bias lights that could be used to increase its sensitivity in low-light environments. These lights could be adjusted either manually or under computer control to shine a uniform, low level of light on the sensor. Once adjusted, the Cyclops would be sensitive to the smallest amount of incident light from an image in low-light situations. Today solid-state digital cameras are ubiquitous. A high-resolution digital camera sensor today may contain 20 million sensor elements, 20,000 times more than the 0.001 megapixel sensor of the Cyclops. Video of Cromemco Cyclops Camera used to control a ball going through a maze. on YouTube Video of Cromemco Cyclops Camera simulation running in an IMSAI simulation. On YouTube Cromemco Cyclops Camera Controller manual.
Cromemco Cyclops Camera manual
A color gel or color filter known as lighting gel or gel, is a transparent colored material, used in theater, event production, photography and cinematography to color light and for color correction. Modern gels are thin sheets of polycarbonate, polyester or other heat-resistant plastics, placed in front of a lighting fixture in the path of the beam. Gels have a limited life in saturated colors and shorter wavelength; the color will fade or melt, depending upon the energy absorption of the color, the sheet will have to be replaced. In permanent installations and some theatrical uses, colored glass filters or dichroic filters are being used; the main drawbacks are a more limited selection. In Shakespearean-era theater, red wine was used in a glass container as a light filter. In days, colored water or silk was used to filter light in the theater. A gelatin base became the material of choice. Gelatin gel was available at least until 1979; the name gel has continued to be used to the present day. Gelatin-based color media had no melting point, the color was cast in the media as opposed to being coated on the surface, both important properties for color media.
It would, char at high temperatures and become brittle once heated, so it was impossible to handle once used in the lighting instrument. By 1945 more heat-tolerant and self-extinguishing acetate-based through-dyed materials were being manufactured. In the U. S. Roscolene was developed to deal with these higher output light sources. Though cheaper, the acetate filters fell out of favor with professional organizations since they could not withstand the higher temperatures produced by the tungsten halogen lamps that came into widespread use in the late 1960s; the acetate-based material was replaced by polycarbonates like polyester-based filters. These materials have superior heat tolerance. Many were transparent film with a surface coating; the first dyed polyester gels were introduced by Berkey-Colortran in 1969 as Gelatran, the original deep-dyed polyester. The Gelatran process is still used today to produce Roscolux. Other color manufacturers, such as Lee Filters and Apollo Design Technology, use a surface applied dye.
Every color manufacturer today uses either polycarbonate or polyester to manufacture their gels. Today's gels can burn out rendering them useless. To help combat this, high-temperature materials – polyester having the highest melting point of 480 °F – can be used to help prolong the life in high-heat output lighting instruments; as instrument design improves, it has become a selling point on many lights to have as little heat radiating from the front of the fixture as possible to help prevent burn-through, help keep the stage and actors cooler during performances. In the 1930s, Strand Electric of London provided the first numbering system for their swatches and with their agents in New York and Sydney the numbering system went round the world. Remnants of this original filter color system exist in the color swatches of today. In the theater, gels are available in single 20 in × 24 in sheets, which are cut down to the appropriate size before use; the size originates from the gelatin days: it is the same as a standard baker's sheet, used to cast the sheets.
In the film industry, gels are cut straight from rolls 24 or 48 in wide and 50 ft long, as the size required may vary from a single practical halogen spotlight in a ceiling to a whole window, so a standard-sized sheet would be impractical. Similar colors may vary between different companies' formulations – for example, many have a color named "bastard amber", but the transmitted color spectrum may be different. For this reason, gel colors are not referred to by name. Apollo Design Technology uses a four digit number based on the visible spectrum to designate and locate specific color transmissions while Rosco used a two digit number for Roscolux, requiring them to prepend some newer gel numbers with a 3 in order to retain this order. Manufacturers use a code consisting of a number combination. Manufacturers produce swatch books, which contain a small piece of each color available, adjacent to its color code, to simplify ordering. Swatch books enable designers and technicians to have a true representation of the manufacturers' range of colors.
Most designers choose a limited color palette for generic applications because it is financially and logistically difficult to have access to all colors for a single show. There are gels for color correction, such as CTB and CTO. Color correction gels alter or correct the color temperature of a light to more match the color temperature of a film negative or the white balance of a digital imager. CTB, blue in appearance, will correct tungsten lights that have a color temperature in the range of 3,200 to 5,700 kelvins to more closely