Delay line memory was a form of computer memory used on some of the earliest digital computers. DDR SDRAM ( double data rate synchronous dynamic random access memory) is a class of memory Integrated circuit used in Computers It achieves nearly twice Static random access memory (SRAM is a type of Semiconductor memory where the word static indicates that unlike ''dynamic'' RAM (DRAM, it does not Z-RAM, short for " zero capacitor RAM " is a new type of Computer memory in development by Innovative Silicon Inc Twin Transistor RAM ( TTRAM) is a new type of Computer memory in development by Renesas The Williams tube or the Williams-Kilburn tube (after inventors Freddie Williams and Tom Kilburn) developed about 1946 or 1947 Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is Computer memory that can retain the stored information A programmable read-only memory ( PROM) or field programmable read-only memory ( FPROM) is a form of digital memory where the setting of each bit is EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable An EPROM, or E rasable P rogrammable '''''R'''ead-'''O'''nly '''M'''emory'', is a type of memory chip that retains its EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed Ferroelectric RAM ( FeRAM or FRAM) is a Random access memory similar in construction to DRAM but uses a Ferroelectric layer instead Magnetoresistive Random Access Memory ( MRAM) is a non-volatile computer memory ( NVRAM) technology which has been under development since The programmable metallization cell, or PMC, is a new form of non-volatile Computer memory being developed at Arizona State University and Phase-change memory (also known as PCM, PRAM, PCRAM, Ovonic Unified Memory, Chalcogenide RAM and C-RAM) is a type This article is about the music device manufacturer For the computer memory system see SONOS. Resistive random-access memory ( RRAM) is a new Non-volatile memory type being developed by Fujitsu, Sharp, Samsung, Micron IBM Racetrack Memory is an experimental Non-volatile memory device under development at IBM 's Almaden Research Center by a team led by Stuart Nano-RAM is a proprietary Computer memory technology from the company Nantero. Drum memory is a magnetic Data storage device and was an early form of Computer memory widely used in the 1950s and into the 1960s invented by Gustav Tauschek Magnetic core memory, or ferrite-core memory, is an early form of Random access Computer memory. Prehistory twistor memory Bubble memory is largely the brainchild of a single person Andrew Bobeck. Twistor is a form of Computer memory, similar to Core memory, formed by wrapping or closing Magnetic tape around a current-carrying wire A digital system uses discrete (discontinuous values usually but not always Symbolized Numerically (hence called "digital" to represent information for A computer is a Machine that manipulates data according to a list of instructions. Like many modern forms of electronic computer memory, delay line memory was a refreshable memory, but as opposed to modern random access memory, delay line memory was serial access. Memory refresh is the process of periodically reading information from an area of Computer memory, and immediately rewriting the read information to the same area with no modifications In the earliest forms of delay line memory, information introduced to the memory in the form of electric pulses was transduced into mechanical waves that propagated relatively slowly through a medium, such as a cylinder filled with a liquid like mercury, or a magnetorestrictive coil, or a piezoelectric crystal. A transducer is a device usually electrical, electronic, Electro-mechanical, Electromagnetic, Photonic, or Photovoltaic Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum Piezoelectricity is the ability of some materials (notably Crystals and certain Ceramics including bone to generate an Electric potential in response to The propagation medium could support the propagation of hundreds or thousands of pulses at any one time. Upon reaching the other end of the propagation medium, the waves were re-transduced into electric pulses, amplified, shaped, and reintroduced to the propagation medium at the beginning, thus refreshing the memory. Generally an amplifier or simply amp, is any device that changes usually increases the amplitude of a signal. In digital telecommunication pulse shaping is the process of changing the waveform of transmitted pulses Accessing a desired part of the propagation medium's memory contents required waiting for the pulses of interest to reach the end of the medium, a wait typically on the order of microseconds. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units Use of a delay line for a computer memory was invented by J. Presper Eckert in the mid-1940s for use in computers such as the EDVAC and the UNIVAC I. John Adam Presper "Pres" Eckert Jr ( April 9, 1919 – June 3, 1995) was an American electrical engineer and EDVAC ( E lectronic D iscrete V ariable A utomatic C omputer) was one of the earliest electronic Computers The UNIVAC I ( U N I V ersal A utomatic C omputer I) was the first commercial computer made in the United States

Genesis in radar

The basic concept of the delay line originated with World War II radar research, as a system to reduce clutter from reflections from the ground and other "fixed" objects. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships

A radar system consists largely of an antenna, a transmitter, a receiver, and a display of some sort. Modern Radar systems typically use some sort of Raster scan display to produce a map-like image The antenna is connected to the transmitter, which sends out a brief pulse of radio energy before being disconnected again. The antenna is then connected to the receiver, which amplifies any reflected signals, and sends them to the display. Objects further from the radar return echos later in time than those located closer to the radar, which the display indicates visually.

Non-moving objects at a fixed distance from the antenna always return a signal after the same delay. This would appear as a fixed spot on the display, making detection of other targets in the area more difficult. Early radars simply aimed their beams away from the ground in order to avoid the majority of this "clutter". This was not an ideal situation by any means; it required careful setup and aiming which was not very easy for smaller mobile radars, and did nothing to remove other sources of clutter like reflections off of certain terrain features.

In order to filter these returns out, two pulses were compared, and returns with common timing are removed. To do this, the signal being sent from the receiver to the display was split in two, with one path leading directly to the display, and the second leading to a delay unit. The delay was carefully tuned to delay the signals some multiple of the time between pulses (the pulse repetition frequency), that way the delayed signal from an earlier pulse would exit the delay unit at the same time as a newer pulse was being received from the antenna. Pulse Repetition Frequency (PRF is the number of pulses transmitted per second by a Radar. One of the signals was then inverted, typically the one from the delay, and the two signals were then combined and sent to the display. Any signal that was at the same location was nullified by the inverted signal from a previous pulse, leaving only the moving objects on the display.

Mercury memory of UNIVAC I (1951)

Several different types of delay systems were invented for this purpose, with one common principle being that the information was stored acoustically in a medium. The UNIVAC I ( U N I V ersal A utomatic C omputer I) was the first commercial computer made in the United States Acoustics is the interdisciplinary science that deals with the study of Sound, Ultrasound and Infrasound (all mechanical waves in gases liquids and solids MIT experimented with a number of systems including glass, quartz, steel and lead. The Japanese deployed a system consisting of a quartz element with a powdered glass coating that reduced surface waves that interfered with proper reception. In Physics, surface wave can refer to a Mechanical wave that propagates along the interface between differing media usually two fluids with different densities The Naval Research Laboratories used steel rods wrapped into a helix, but this was useful only for low frequencies under 1 MHz. Raytheon used a magnesium alloy originally developed for making bells. ^[1]

The first practical de-cluttering system based on the concept was developed by J. Presper Eckert at the University of Pennsylvania's Moore School of Electrical Engineering. John Adam Presper "Pres" Eckert Jr ( April 9, 1919 – June 3, 1995) was an American electrical engineer and The University of Pennsylvania (also known as Penn) is a private University located in Philadelphia, Pennsylvania, USA. Moore School of Electrical Engineering at the University of Pennsylvania came into existence as a result of an endowment from Alfred Fitler Moore on June 4, 1923 His solution used a column of mercury with piezo crystal transducers (a combination of speaker and microphone) at either end. Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum Piezoelectricity is the ability of some materials (notably Crystals and certain Ceramics including bone to generate an Electric potential in response to A transducer is a device usually electrical, electronic, Electro-mechanical, Electromagnetic, Photonic, or Photovoltaic Signals from the radar amplifier were sent to the piezo at one end of the tube, which would cause the transducer to pulse and generate a small wave in the mercury. The wave would quickly travel to the far end of the tube, where it would be read back out by the other piezo, inverted, and sent to the display. Careful mechanical arrangement was needed to ensure the delay time matched the inter-pulse timing of the particular radar being used.

All of these systems were suitable for conversion into a computer memory. The key was to recycle the signals within the memory system so they would not disappear after traveling through the delay. This was relatively easy to arrange with simple electronics.

Acoustic delay lines

Mercury delay lines

After the war Eckert turned his attention to computer development, which was a topic of some interest at the time. One problem with practical development was the lack of a suitable memory device, and Eckert's work on the radar delays meant he had a major advantage over other researchers in this regard.

For a computer application the timing was still critical, but for a different reason. Conventional computers have a natural "cycle time" needed to complete an operation, the start and end of which typically consist of reading or writing memory. Thus the delay lines had to be timed such that the pulses would arrive at the receiver just as the computer was ready to read it. Typically many pulses would be "in flight" through the delay, and the computer would count the pulses by comparing to a master clock to find the particular bit it was looking for.

Mercury was used because the acoustic impedance of mercury is almost exactly the same as that of the piezoelectric quartz crystals; this minimized the energy loss and the echoes when the signal was transmitted from crystal to medium and back again. The acoustic impedance Z (or sound impedance) is a frequency f dependent parameter and is very useful for example for describing the behaviour of musical The high speed of sound in mercury (1450 m/s) meant that the time needed to wait for a pulse to arrive at the receiving end was less than it would have been with a slower medium, such as air, but it also meant that the total number of pulses that could be stored in any reasonably sized column of mercury was limited. Sound is a vibration that travels through an elastic medium as a Wave. Other technical drawbacks of mercury included its weight, its cost, and its toxicity. Moreover, to get the acoustic impedances to match as closely as possible, the mercury had to be kept at a temperature of 40 degrees Celsius, which made servicing the tubes hot and uncomfortable work.

A considerable amount of engineering was needed to maintain a "clean" signal inside the tube. Large transducers were used to generate a very tight "beam" of sound that would not touch the walls of the tube, and care had to be taken to eliminate reflections off the far end of the tubes. The tightness of the beam then required considerable tuning to make sure the two piezos were pointed directly at each other. Since the speed of sound changes with temperature (because of the change in density with temperature) the tubes were heated in large ovens to keep them at a precise temperature. Other systems instead adjusted the computer clock rate according to the ambient temperature to achieve the same effect.

EDSAC, designed to be the first stored-program digital computer, began operation with 512 35-bit words of memory, stored in 32 delay lines holding 576 bits each (a 36th bit was added to every word as a start/stop indicator). Electronic Delay Storage Automatic Calculator ( EDSAC) was an early British Computer. The von Neumann architecture is a design model for a stored-program Digital computer that uses a processing unit and a single separate storage structure A computer is a Machine that manipulates data according to a list of instructions. In Computing, " word " is a term for the natural unit of data used by a particular computer design In the UNIVAC I this was reduced somewhat, each column stored 120 bits (although the term "bit" was not in popular use at the time), requiring seven large memory units with 18 columns each to make up a 1000-word store. The UNIVAC I ( U N I V ersal A utomatic C omputer I) was the first commercial computer made in the United States A bit is a binary digit, taking a value of either 0 or 1 Binary digits are a basic unit of Information storage and communication Combined with their support circuitry and amplifiers, the memory subsystem formed its own walk-in room. Generally an amplifier or simply amp, is any device that changes usually increases the amplitude of a signal. A room, in Architecture, is any distinguishable space within a structure The average access time was about 222 microseconds, which was considerably faster than the mechanical systems used on earlier computers. To help compare Orders of magnitude of different Times this page lists times between 10&minus6 seconds and 10&minus5 seconds (1 micro

Magnetostrictive delay lines

A later version of the delay line used metal wires as the storage medium. A wire is a single usually cylindrical, elongated string of drawn Metal. Transducers were built by applying the magnetostrictive effect; small pieces of a magnetostrictive material, typically nickel, were attached to either side of the end of the wire, inside an electromagnet. Magnetostriction is a property of Ferromagnetic materials that causes them to change their shape when subjected to a Magnetic field. Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 When bits from the computer entered the magnets the nickel would contract or expand (based on the polarity) and twist the end of the wire. The resulting torsional wave would then move down the wire just as the sound wave did down the mercury column. In most cases the entire wire was made of the same material.

Unlike the compressive wave, however, the torsional waves are considerably more resistant to problems caused by mechanical imperfections, so much so that the wires could be wound into a loose coil and pinned to a board. In Solid mechanics, torsion is the twisting of an object due to an applied Torque. Due to their ability to be coiled, the wire-based systems could be built as "long" as needed, and tended to hold considerably more data per unit; 1k units were typical on a board only 1 foot square. A kilobit is a unit of information abbreviated kbit (or kb) The standard definition is 1 kilobit = 103 bit = 1000 Bit. Of course this also meant that the time needed to find a particular bit was somewhat longer as it traveled through the wire, and access times on the order of 500 microseconds were typical.

Delay line memory was far less expensive and far more reliable per bit than flip-flops made from tubes, and yet far faster than a latching relay. In Digital circuits a flip-flop is a term referring to an Electronic circuit (a Bistable Multivibrator) that has two stable states and thereby This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. A relay is an electrical Switch that opens and closes under the control of another Electrical circuit. It was used right into the late 1960s, notably on British commercial machines like the LEO I and various Ferranti machines. The 1960s decade refers to the years from the beginning of 1960 to the end of 1969 The British LEO I ( L yons E lectronic O ffice I) Computer ran its first business application in 1951 Ferranti or Ferranti International plc was a major UK Electrical engineering and equipment firm known primarily for defence Electronics and They were also used very successfully in several models of early desktop electronic calculator, including the Friden EC130 (1964) and EC132, the Olivetti Programma 101 desktop programmable calculator introduced in 1965, and the Litton Monroe Epic 2000 and 3000 programmable calculators of 1967. A calculator is device for performing mathematical calculations distinguished from a Computer by having a limited problem solving ability and an interface optimized for interactive Year 1964 ( MCMLXIV) was a Leap year starting on Wednesday (link will display full calendar of the 1964 Gregorian calendar. Ing C Olivetti & Co SpA, known as Olivetti, is an Italian manufacturer of Computers printers and other business machines The Programma 101 was a printing Programmable calculator manufactured by Olivetti in 1965 Programmable calculators are Calculators capable of being programmed much like a Computer. Year 1965 ( MCMLXV) was a Common year starting on Friday (link will display full calendar of the 1965 Gregorian calendar. The Monroe EPIC was a programmable Calculator come on the market in the 1960s Programmable calculators are Calculators capable of being programmed much like a Computer. Year 1967 ( MCMLXVII) was a Common year starting on Sunday (link will display full calendar of the 1967 Gregorian calendar.

Piezoelectric delay lines

An ultrasonic delay line from a Colour-TV; it delays the colour signal for 64µs
Manufacturer: VEB ELFEMA Mittweida (GDR) in 1980

A similar solution to the magnetostrictive system was to use delay lines made entirely of a piezo material, typically quartz. The German Democratic Republic ( GDR; Deutsche Demokratische Republik DDR; commonly known in English as East Germany) was a Socialist state Current fed into one end of the crystal would generate a compressive wave that would flow to the other end where it could be read out. In effect, piezoelectric delays simply replaced the mercury and transducers of a conventional mercury delay line with a single unit combining both. However these solutions were fairly rare; building crystals of the required quality in large sizes was not easy, limiting them to small sizes, and thus small amounts of data storage.

A better and more widespread use of piezoelectric delays was in European television sets. The European PAL standard for color broadcasts compares the signal from two subsequent lines in order to avoid color shifting due to small phase shifts. PAL, short for Phase Alternating Line, is a colour -encoding system used in Broadcast television systems in large parts of the world By comparing two lines, one inverted, the shifting is averaged out and returns a signal more closely matching the original even under interference. In order to compare the two lines, a piezo delay tuned to the timing of the lines, 64 µs, is inserted in the signal path. The delay unit is shaped to "fold" the beam multiple times through the crystal, greatly reducing its length and producing a small square-ish device.

Electric delay lines

Electric delay line (450ns), consisting of enamelled copper wire, wound around a metal tube

Electric delay lines are used for shorter delay times (ns to several µs). They consist of a long electric line or are made of discrete inductors and capacitors, which are arranged in a chain. To shorten the total length of the line it can be wound around a metal tube, getting some more capacitance against ground and also more inductance due to the wire windings, which are laying close together.

Other examples are:

• short coaxial or microstrip lines for phase matching in high frequency circuits or antennas
• hollow resonator lines in magnetrons and klystrons as helices in travelling wave tubes to match the velocity of the electrons to the velocity of the electromagnetic waves
• undulators in free electron lasers

Another way to create a delay time is to implement a delay line in an integrated circuit storage device. Microstrip is a type of electrical Transmission line which can be fabricated using Printed circuit board technology and is used to convey Microwave -frequency An antenna is a Transducer designed to transmit or Receive electromagnetic waves In other words antennas convert electromagnetic waves into A cavity magnetron is a high-powered Vacuum tube that generates coherent Microwaves They are commonly found in Microwave ovens as well as various A klystron is a specialized linear-beam Vacuum tube (evacuated electron tube A traveling-wave tube (TWT is an electronic device used to amplify Radio frequency signals to high power usually in an electronic assembly known as a traveling-wave Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. An undulator is an Insertion device from high-energy physics and usually part of a larger installation a Synchrotron Storage ring. A free-electron laser, or FEL is a Laser that shares the same optical properties as conventional lasers such as emitting a Beam consisting of coherent Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside This can be done digitally or with a discrete analogue method. The analogue one uses charge coupled devices (CCD), which transport a stored electric charge stepwise from one end to the other. A charge-coupled device ( CCD) is an analog Shift register, that enables the transportation of analog signals (electric charges through successive stages (capacitors Both methods are bandwidth limited at the upper end to the half of the clock frequency, which determines the steps of transportation.

References

External links

• Acoustic Delay Line Memory – has an image of a Ferranti wire-based system about half-way down the page
• Delay line memories – contains a diagram of the magnetostrictive transducer
• Litton Monroe Epic 3000 - Shows details of the torsion delay lines inside this electronic calculator of 1967.
• Magnetostrictive memory, still used in a German computer museum

• U.S. Patent 2,629,827  "Memory System", Eckert-Mauchly Computer Corporation, filed October 1947, patented February 1953