Computers 4A: Origin of Hardware


laser1I was about to say that there are exceptions to all rules and admit that the laser, something also integral to computer data recording, came about as a result of the theoretical work of Albert Einstein. However, reading various versions of the history of his Nobel prize, the jury is still out, until I find some information that gives clear answers on the subject. It seems that no two writers agree as to exactly what he received the prize for, and this indecision apparently also applies to the Nobel committee who made the award after a year of deliberation. Their decision appears to be political rather than scientific or technical. The trend continues today. “As is well known Einstein did not get the Nobel Prize for his relativity theories due to strong disbeliefs in those theories among some influential members of the Royal Swedish Academy of Sciences. The 1911 Nobel Laureate in Physiology or Medicine Allvar Gullstrand was of the opinion that the correctness of Einstein’s special relativity theory rested on belief – not proven facts, and the general relativity theory could in his opinion not stand a critical analysis…(as is the case to this day, see the physics page

The Nobel Committee avoids committing itself to the particle concept.
Light-quanta or with modern terminology, photons, were explicitly mentioned in the reports on which the prize decision rested only in connection with emission and absorption processes. The Committee says that the most important application of Einstein’s photoelectric law and also its most convincing confirmation has come from the use Bohr made of it in his theory of atoms, which explains a vast amount of spectroscopic data.

einstein bohrBohr–Einstein debates
Wiki: Einstein was the first physicist to say that Planck’s discovery of the quantum (h) would require a rewriting of the laws of physics.


planckMax Plank

Even the history of this stuff is counterintuitive…..

See page on Electron particles



Laser “invention”?

Joseph Webber inducted in May 1988 for conceiving the idea of coherent microwave emissions which led to the development of the maser and laser.

1951 Joseph_Weber
Wiki: Professor of engineering Joseph_Weber submitted a paper in 1951 for the June 1952 Electron Tube Research Conference held in Ottawa, which was the earliest public lecture on the principles behind the laser and the maser. After this presentation, RCA asked Weber to give a seminar on this idea, and Charles Hard Townes asked him for a copy of the paper. Townes was working along similar lines, as were Nikolay Basov and Aleksandr Prokhorov. Although Weber was jointly nominated for the Nobel Prize in Physics in 1962 and 1963 for his contributions to the development of the laser, it was Townes, Basov, and Prokhorov, the first to build working prototypes of these devices, who received the 1964 Prize, “for fundamental work in the field of quantum electronics, which has led to the construction of oscillators and amplifiers based on the maser–laser principle.

His interest in general relativity led Weber to use a 1955–1956 sabbatical, funded by a Guggenheim Fellowship, to study gravitational radiation with John Archibald Wheeler at the Institute for Advanced Study in Princeton, NJ and the Lorentz Institute for Theoretical Physics at the University of Leiden in the Netherlands. At the time, the existence of gravitational waves was not widely accepted. Weber was the first to make a real attempt to detect these waves. After he began publishing papers on the detection of gravitational waves, he moved from the Engineering department to the Physics department at Maryland.

Physicists weren’t always so kind about Weber.

Charles Misner He was unwilling or unable to admit that he might have made an error. To others in the field, who were trying to get plans for what would become LIGO funded, that made him a threat.
Even if Weber’s work was discredited, there was a chance that one of the bureaucrats who controlled the funding could decide to back him, Boyd said.
Charles Misner, an emeritus professor of physics at the University of Maryland, said that concern made people wary of giving Weber some sort of prize during his lifetime.

Nobel Prize in physics awarded to 3 Americans for work on gravity waves

“But if we give him a prize he’ll make speeches,” Misner recalled people saying. “Nobody wanted to see him talk Congress into canceling all their money.”
Virginia Trimble, an astronomer at the University of California, Irvine and Weber’s second wife, said it was only after Weber’s death that his contributions began to be publicly recognized.
“They were nasty until he died because of competition for funding,” she said. “Once he died and wasn’t competing for money, slowly but surely all the people who had gotten the money said yes, he founded their field.”

It must be noted at this point that being a successful physicist also entails being a complete bastard, prepared to destroy the career of a fellow researcher.


1954, Charles Townes and Arthur Schawlow invented the maser (microwave amplification by stimulated emission of radiation), using ammonia gas and microwave radiation – the maser was invented before the (optical) laser.
(Again this is not invention but development.)

Laser Time-line

1958 Gordon Gould
Gordon Gould was the first person to use the word “laser”. There is good reason to believe that Gordon Gould made the first light laser. Gould was a doctoral student at Columbia University under Charles Townes, the inventor of the maser. Gordon Gould was inspired to build his optical laser starting in 1958. He failed to file for a patent on his invention until 1959. As a result, Gordon Gould’s patent was refused and his technology was exploited by others. It took until 1977 for Gordon Gould to finally win his patent war and receive his first patent for the laser.

1960 Theodore H. (Ted) Maiman
Maiman, a physicist at Hughes Research Laboratories in Malibu, Calif., constructs the first laser using a cylinder of synthetic ruby measuring 1 cm in diameter and 2 cm long, with the ends silver-coated to make them reflective and able to serve as a Fabry-Perot resonator. Maiman uses photographic flashlamps as the laser’s pump source.

Then everyone jumps on the bandwagon:
1956: Bloembergen, N. – Solid-state maser- [Proposal for a new type of solid state maser] at Harvard University.

1958: Schawlow, A.L. and Townes, C.H. – Proposed the realization of masers for light and infrared at Columbia University .

1960 Ali Javan: The first gas laser (helium neon) was invented by Ali Javan in 1960. The gas laser was the first continuous-light laser and the first to operate “on the principle of converting electrical energy to a laser light output.” It has been used in many practical applications.
The gas laser was the first continuous-light laser and the first laser to operate “on the principle of converting electrical energy to a laser light output.” By definition, “a gas laser is a laser in which an electric current is discharged through a gas to produce light.” Ali Javan received U.S. patent #3,149,290 together with William Bennett for the “Gas Optical Maser”. Ali Javan first tested his invention on December 12, 1960.
The gas laser laid the foundation for fiber optic communication. Laser telecommunication via fiber optics is known to be the key technology used in today’s Internet.[21] Helium-Neon gas lasers were the first lasers to be mass-produced. They were used in everything from UPC checkout scanners, video disc players to medical and monitoring technologies and laser printers. Although they have been largely replaced by diode-pumped solid state lasers and laser diodes, they are now used principally for specialized applications such as interferometry and holography due to their long coherence length and Gaussian irradiance profile.

1960: Maiman, T.H. – Realization of first working LASER based on Ruby at Hughes Research Laboratories.

1961: Javan, A., Bennet, W.R. and Herriot, D.R. – First gas laser : Helium- Neon (He-Ne laser) at Bell Laboratories.

1961: Fox, A.G., Li, T. – Theory of optical resonators at Bell Laboratories.

1962: Hall,R. – First Semiconductor laser (Gallium-Arsenide laser) at General Electric Labs.

1962: McClung,F.J and Hellwarth, R.W. – Giant pulse generation / Q-Switching.

1962: Johnson, L.F., Boyd, G.D., Nassau, K and Sodden, R.R. – Continuous wave solid-state laser.

1964: Geusic, J.E., Markos, H.M., Van Uiteit, L.G. – Development of first working Nd:YAG LASER at Bell Labs.

1964: Patel, C.K.N. – Development of CO2 LASER at Bell Labs.

1964: Bridges, W. – Development of Argon Ion LASER a Hughes Labs.

1965: Pimentel, G. and Kasper, J. V. V. – First chemical LASER at University of California, Berkley.

1965: Bloembergen, N. – Wave propagation in nonlinear media.

1966: Silfvast, W., Fowles, G. and Hopkins – First metal vapor LASER – Zn/Cd – at University of Utah.

1966: Walter, W.T., Solomon, N., Piltch, M and Gould, G. – Metal vapor laser.

1966: Sorokin, P. and Lankard, J. – Demonstration of first Dye Laser action at IBM Labs.

1966: AVCO Research Laboratory, USA. – First Gas Dynamic Laser based on CO2

1970: Nikolai Basov’s Group – First Excimer LASER at Lebedev Labs, Moscow based on Xenon (Xe) only.

1974: Ewing, J.J. and Brau, C. – First rare gas halide excimer at Avco Everet Labs.

1977: John M J Madey’s Group – First free electron laser at Stanford University.

1977: McDermott, W.E., Pehelkin, N.R,. Benard, D.J and Bousek, R.R. – Chemical Oxygen Iodine Laser (COIL).

1980: Geoffrey Pert’s Group – First report of X-ray lasing action, Hull University, UK.

1984: Dennis Matthew’s Group – First reported demonstration of a “laboratory” X-ray laser from Lawrence Livermore Labs.

1999: Herbelin,J.M., Henshaw, T.L., Rafferty, B.D., Anderson, B.T., Tate, R.F., Madden, T.J., Mankey II, G.C and Hager, G.D. – All Gas-Phase Chemical Iodine Laser (AGIL).

2001: Lawrence Livermore National Laboratory – Solid State Heat Capacity Laser (SSHCL).
Much of the above thanks to:

Oskar Heil

Oskar Heil

Oskar Heil (20 March 1908 – 1994, San Mateo, California) was a German electrical engineer and inventor. He studied physics, chemistry, mathematics, and music at the Georg-August University of Göttingen and was awarded his PhD in 1933, for his work on molecular spectroscopy.

Field-effect transistor
Heil is mentioned as the inventor of an early transistor-like device (see also History of the transistor), based on several patents that were issued to him.[3][4]

JFETS: The New Frontier states: “Field-effect transistors (FETs) have been around for a long time; in fact, they were invented, at least theoretically, before the bipolar transistors. The basic principle of the FET has been known since J.E. Lilienfeld’s US patent from 1930,[5] and Oscar Heil described the possibility of controlling the resistance in a semiconducting material with an electric field in a British patent in 1935.”

Scotching the laser
About 20 years ago, Dr (Oskar) Heil told me that, when he was working in Germany, a co-worker developed a device for studying quantum levels in ionized gases. He joked that he talked the guy out of working on it, because it had no practical use — and thereby stymied the invention of the gas laser! (See above) (“No practical use” was what Dr Heil said. This struck me as odd, because scientists generally don’t worry about whether research has “practical” use.)


CD, DVD, Laser Disk, Video Disk


David Paul Gregg

Dr. David Paul Gregg, according to Wiki, is credited with invention of the optical disk (CD, DVD, Laser Disk) in 1958. However, there do seem to be a string of complaints about the contents of the Wiki article on this subject. The author of these pages has no idea why there should be so much confusion about a relatively modern technology?

Here is an example – WikiTalk: “I have a problem with the intro to this section: The Compact Disc is not an invention: it is the convergence of a series of enabling technologies, such as laser technology, mechanics, electronics, and coding technology. Therefore, nobody can claim that he or she is the inventor of the Compact Disc…Is it just a digital version of the Videodisc developed in the 60s and 70s? ” 83

…and recording in digital is no different from recording in analogue. The discussion continues with a somewhat (by now) lame argument that we have come across before in these pages: WikiTalk again: “The same sort of argument could be made for just about any invention. Take the automobile – we couldn’t have cars if someone hadn’t invented the wheel, wagons, metalurgy, internal combustion engines, etc. And of course we never would have CDs if nobody had invented lasers, transistors, computers, digital audio formats, etc. But just because an invention builds on previous inventions doesn’t mean that it’s any less an invention in its own right. Credit for the invention should be given to Philips and Sony and their “joint taskforce of engineers.”” 84
But it’s all about the fact that Philips and Sony did not invent them, they developed them.

This argument is based on the assumption that some of the examples given: “lasers, transistors, computers, digital audio formats, etc.” are automatically assumed to be the work (or theory) of academics. The Compact Disc “invention” is attributed to an academic who is deserving of the accolade if the circular reasoning is accepted. The “engineering task-force” is assumed to be working on the instructions of the academic. The insecurity of the scientific community is such that it deems it necessary to lay-claim to every new technology even at a time when the patent claimant is making pots of money from the idea.

Wiki says: “Dr. David Paul Gregg was the inventor of the optical disc (disk). Gregg was inspired to create the optical disc in 1958 while working at Californian electronics company, Westrex. He (His) first patent for a “Videodisk” was filed in March 1962 (USPO 3350503) where he looks to advance electron beam recording and reproducing. Gregg went to work at 3M’s Mincom division with experienced television videotape engineers Wayne Johnson and Dean De Moss. The three men subsequently filed patents to cover a disc recording system, a way to duplicate discs, and reproducing TV signals from photographic discs. When Mincom contracted Stanford’s SRI to further the research, Gregg left and formed his own company Gauss Electrophysics.” 85

Videodisc History Time-line
Mostly from Wiki:
1898 “E & H T Anthony, a camera maker based in New York, marketed in 1898 a combination motion picture camera and projector called “The Spiral” that could capture 200 images arranged in a spiral on an 8 inch diameter glass plate, which when played back at 16 frames per second would give a running time of 13 seconds.

1907   Theodore Brown patented (UK patent GB190714493) a photographic disk system in 1907 recording approximately 1,200 images in a spiral of pictures on a 10 inch disk. Played back at 16 frames per second, the disk could provide around one and a quarter minutes of material. The system was marketed as the Urban Spirograph by Charles Urban, and disks were produced – but it soon disappeared.

1930s John Logie Baird, created the Phonovision system in the early 1930s, which mechanically produced about four frames per second. The system was not successful.” 86 But someone did get it to work:


1941 Video jukebox “Video jukebox from 1941 that played a stack of VideoDiscs and was the television equivalent of a Wurlitzer Jukebox. The image was seen through the aperture at the top, and the sound recorded on the discs came out the large round speaker at the bottom. A stack of 10″ VideoDiscs can be seen at the left side of the large opening in the middle, with any one of the discs being selectable using the row of buttons underneath the opening. The grooved discs rotated at 100 RPM and provided about a minute of playback. This system appeared in the December 1941 issue of Popular Mechanics, so the advent of World War II halted any commercial implementation of the VideoDisc jukebox. Manufacture of televisions was also halted during the war.” 87

1950’s P.M.G Toulon,
P.M.G Toulon, a French inventor working at Westinghouse Electric during the 1950s and 1960s patented a system in 1952 (US Patent 3198880) which used a slow spinning disc with a spiral track of photographically 1.5 millimeter wide recorded frames, along with a flying spot scanner, which swept over them to produce a video image. This was intended to be synchronously combined with playback from a vinyl record. It appears a working system was never produced. It has similarities with the tape based Electronic Video Recording system, which was released for professional use.  88

Laser Turntable

Laser Turntable for standard vinyl record reproduction

1977 William K. Heine Wiki: He presented a paper entitled A Laser Scanning Phonograph Record Player to the 57th Audio Engineering Society (AES) convention in May 1977. The paper details a method developed by Heine that employs a single 2.2 mW Helium–neon laser for both tracking a record groove and reproducing the stereo audio of a phonograph in real time. In development since 1972, the working prototype was named the “LASERPHONE” and the methods it used for playback was awarded U.S. Patent 3,992,593 on 16 November 1976.[1] Heine concluded in his paper that he hoped his work would increase interest in using lasers for phonographic playback.


Digital Recording

 1938 Alec Harley Reeves Digital Transmissions and Recording
Wiki and “Engineer, Alec Harley Reeves, (1902 – 1971) recognised the potential of pulse-code modulation (What are now called digital transmissions or recordings) for reducing noise when speech is transmitted over long distances. He patented the invention in 1938, (that 1930’s deadline again) but it was impractical at the time due to the need for the complex circuits needed with valve/vacuum tube technology. It only became feasible in the 1950’s with the introduction of the transistor. He was also involved in the invention of optical fibres.”. 89

Reeves was a pioneer of semiconductor devices and among the first to exploit the possibility of using light to carry information. When ‘waveguides’ – pipes carrying high frequency signals – failed to work, Reeves thought of glass fibres. In the late 1960’s, he inspired and led the team under Charles Kao and George Hockham (See below) that created the world’s first practical optical fibre system.”
Open-minded, he experimented with the paranormal and believed he was in regular contact with the 19th century inventor of DC electrical generation, Michael Faraday. (It’s not unusual to find a spiritual element in the lives of those who have pioneering ideas, but this is not considered to be sound scientific methodology. 😉  90

There is very little scope for inventors these days and almost no forums where they can exchange ideas. New ideas are frowned upon and inventors are often accused of pseudo-science by sceptics and sceptical scientists who often never have an original idea in their lives.


Fibre Optics

Like most “modern, original” ideas in these pages, fibre optics is an old technology invented by enthusiasts rather than the wise and prudent qualified academic scientists. But when someone gets a Nobel prize, I like to look at the history “As far back as Roman times, glass has been drawn into fibers.” 115


“Fibre optics, though used extensively in the modern world, is a fairly simple, and relatively old, technology. Guiding of light by refraction, the principle that makes fibre optics possible, was first demonstrated by Daniel Colladon and Jacques Babinet in Paris in the early 1840s. John Tyndall included a demonstration of it in his public lectures in London, 12 years later.” 116

1841 Daniel Colladon

Wiki: “Colladon studied law but then worked in the laboratories of Ampere and Fourier.” 117 He wrote: “I managed to illuminate the interior of a stream (of water)in a dark space. I have discovered that this strange arrangement offers in results one of the most beautiful, and most curious experiments that one can perform in a course on Optics.” Colladon demonstrated light guiding in water jets through a number of public performances to the urban intelligentsia of Paris. Auguste de la Rive, another Geneva Physicist, duplicated Colladon’s experiment using electric arc light. Colladon designed a spectacular device using arc light for Conservatory of Arts and Science of Paris in 1841, Oct..” 118

1842 Jacques Babinet

Wiki: “Babinet started his studies at the Lyce Napolon, but was persuaded to abandon a legal education for the pursuit of science. Arago recalled that Jacques Babinet, a French specialist in Optics had made similar demonstrations in Paris. He focused candle light on to the bottom of a glass bottle as he poured a thin stream of water from the top. TIR guided the light along the jet. Arago asked Babinet to write down his work, but Babinet did not think that the work is very important. Yet he made a comment that “the idea also works very well with a glass shaft curved in what ever manner and I had indicated that (it could be used) to illuminate the inside of the mouth (Comptes Rendes 15, Oct. 24, 1842). After sending his letter to Arago, Babinet never returned to guiding of light before he died in 1872.” 119

1870 John Tyndall “In 1870, John Tyndall, (teacher and surveyor), using a jet of water that flowed from one container to another and a beam of light, demonstrated that light used internal reflection to follow a specific path.” 120

It is but a small step from liquid to solid, but:

1880 William Wheeling “William Wheeling, in 1880, patented a method of light transfer called piping light. Wheeling believed that by using mirrored pipes branching off from a single source of illumination, i.e. a bright electric arc, he could send the light to many different rooms… “ 121

1880 Alexander Graham Bell and Wiki: “That same year,(1880) Alexander Graham Bell developed an optical voice transmission system he called the photophone. The photophone used free-space light to carry the human voice 200 meters.” 122 123

“Bell received numerous honorary degrees from colleges and universities, to the point that the requests almost became burdensome…But Bell’s only academic qualification was professor of Vocal Physiology and Elocution at the Boston University School of Oratory. 124
Academia wanted Bell within its ranks for the prestige and so he became an adopted son of science.

1888 Roth and Reuss of Vienna “In 1888, the medical team of Roth and Reuss of Vienna used bent glass rods to illuminate body cavities.

1895 Henry Saint-Rene

In 1895, French engineer Henry Saint-Rene designed a system of bent glass rods for guiding light images in an attempt at early television.

In 1898, American David Smith applied for a patent on a bent glass rod device to be used as a surgical lamp.

1920’s,  John Logie Baird

In the 1920’s, Englishman John Logie Baird and American Clarence W. Hansell patented the idea of using arrays of transparent rods to transmit images for television and facsimiles respectively.

1930 Heinrich Lamm

In 1930,(that magical decade again) German medical student, Heinrich Lamm was the first person to assemble a bundle of optical fibers to carry an image. Lamm’s goal was to look inside inaccessible parts of the body. During his experiments, he reported transmitting the image of a light bulb. The image was of poor quality, however. His effort to file a patent was denied because of Hansell’s British patent. 125 and Wiki: “Fiber optic technology experienced a phenomenal rate of progress in the second half of the twentieth century. Early success came during the 1950s with the development of the fiberscope. This image-transmitting device, which used the first practical all-glass fiber, was concurrently devised by Brian OBrien at the American Optical Company and Narinder Kapany (who first coined the term fiber optics in 1956)” 126

Holger Moeller“In 1951, Holger Moeller applied for a Danish patent on fiber-optic imaging in which he proposed cladding glass or plastic fibers with a transparent low-index material, but was denied because of Baird and Hansell’s patents. Three years later, Abraham Van Heel and Harold H. Hopkins presented imaging bundles in the British journal Nature at separate times. Van Heel later produced a cladded fiber system that greatly reduced signal interference and crosstalk between fibers.” 127

It’s at this point, as far as these researches are concerned, that academia seems to have gotten its foot in the fibre optical front-door – a theory that enables them to claim the technology as their own and once a theory is in place the academics have control of development.

Believe it or not?

Wiki: “The Honorable Sir Charles Kuen Kao, GBM,KBE, FRS, FREng, (born 4 November 1933) is a pioneer in the development and use of fiber optics in telecommunications. Kao, known as the “Godfather of Broadband”, “Father of Fiber Optics” or “Father of Fiber Optic Communications”, was awarded half of the 2009 Nobel Prize in Physics for “ground-breaking achievements concerning the transmission of light in fibres for optical communication” 128

1920’s OCR character reading device

1920s The Reading Machine (first OCR character reading device) of Gustav Tauschek


Patent drawing of Gustav Tauschek’s character reading machine A lot of people dreamed of a machine which could read characters and numerals, but it seems the first OCR (Optical Character Recognition) device was developed in late 1920s by the Austrian engineer Gustav Tauschek (1899-1945), who in 1929 obtained a patent on OCR (so called Reading Machine) in Germany, followed by Paul Handel who obtained a US patent on OCR (so called Statistical Machine) in USA in 1933 (U.S. Patent 1915993). In 1935 Tauschek was also granted a US patent on his machine (U.S. Patent 2026329).

Tauschek was a genius self-taught Viennese engineer, with more than 200 patents in the computing field to his credit, who used to work for IBM and who besides the first OCR device, invented also many devices and systems for the punch-card machinery, as well as the magnetic drum-memory.

Inkjet and other Printers

1867 Lord Kelvin Inkjet

Wiki: The continuous inkjet (CIJ) method is used commercially for marking and coding of products and packages. The idea was first patented in 1867 by Lord Kelvin, and the first commercial devices (medical strip chart recorders) were introduced in 1951 by Siemens.  91 For all its originality, the idea behind the inkjet is far from new. As long ago as 1867, William Thomson (later known as Lord Kelvin) was granted a patent for “Receiving or Recording Instruments for Electrical Telegraphers” which used electrostatic forces to control the release of ink drops on to paper. 92
As it turns out, the Syphon Recorder was not a success, despite being the first device to use an electrostatic charge to print a code. It was a pen recorder with an electrostatically controlled ink flow that drew a wiggly line on a role of tape – not a printer. But reverse engineering the name of a famous scientists onto a page at Wiki is what its editors do best.

Lord Kelvin’s Syphon Recorder

1937 Xerox In 1937, the process called Xerography was invented by American law student Chester Carlson. Carlson had invented a copying process based on electrostatic energy. Xerography became commercially available in 1950 by the Xerox Corporation. Xerography comes from the Greek for “dry writing”.93

1948    Rune Elmqvist Elmqvist

Wiki: “Rune Elmqvist – Elmqvist initially worked as a medical doctor (having trained in Lund), but later worked as an engineer and inventor.
In 1948, he developed the first inkjet ECG printer which he called the mingograph while working at Elema-Schnander, a company which later became Siemens-Elema. In 1957 he received an honorary doctorate.” 94 Well he would, it’s very flattering.

1972 Daisy Wheel

Wiki: In 1972 a team at Diablo Systems led by engineer David S. Lee developed the first commercially successful daisy wheel printer, a device that was faster and more flexible than IBM’s golf-ball devices, being capable of 30 cps (characters per second), whereas IBM’s Selectric operated at 13.4 cps. 95


I personally, see no justification in any of the above that would lead anyone to attribute the development of the computer to academic science, the scientific method, or an education in physics. Most of the names that appear above were not qualified scientists or physicists in the accepted understanding of the word. If the requirement for an inventive mind depends on a scientific education then most of the names above would be those of scientists and they clearly are not.
It’s not possible to educate someone to be inventive or innovative, this depends on individual imagination, something discouraged by science unless accompanied by scientific qualification. This in turn seems to discourage independent critical thinking outside of the scientific box and so nothing new to science is discovered and scientists don’t usually invent.

See the page on transistor history


Numbered references Computer History
Wiki is frequently used, not because it’s the best reference work but because it is the most accessible.

See also: