A teleprinter is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point and point-to-multipoint configurations. They were used in telegraphy, which developed in the late 1830s and 1840s as the first use of electrical engineering; the machines were adapted to provide a user interface to early mainframe computers and minicomputers, sending typed data to the computer and printing the response. Some models could be used to create punched tape for data storage and to read back such tape for local printing or transmission. Teleprinters could use a variety of different communication media; these included a simple pair of wires. A teleprinter attached to a modem could communicate through standard switched public telephone lines; this latter configuration was used to connect teleprinters to remote computers in time-sharing environments. Teleprinters have been replaced by electronic computer terminals which have a computer monitor instead of a printer.
Teleprinters are still used in the aviation industry, variations called Telecommunications Devices for the Deaf are used by the hearing impaired for typed communications over ordinary telephone lines. The teleprinter evolved through a series of inventions by a number of engineers, including Samuel Morse, Alexander Bain, Royal Earl House, David Edward Hughes, Emile Baudot, Donald Murray, Charles L. Krum, Edward Kleinschmidt and Frederick G. Creed. Teleprinters were invented in order to send and receive messages without the need for operators trained in the use of Morse code. A system of two teleprinters, with one operator trained to use a keyboard, replaced two trained Morse code operators; the teleprinter system improved message speed and delivery time, making it possible for messages to be flashed across a country with little manual intervention. There were a number of parallel developments on both sides of the Atlantic Ocean. In 1835 Samuel Morse devised a recording telegraph, Morse code was born.
Morse's instrument used a current to displace an electromagnet, which moved a marker, therefore recording the breaks in the current. Cooke & Wheatstone received a British patent covering telegraphy in 1837 and a second one in 1840 which described a type-printing telegraph with steel type fixed at the tips of petals of a rotating brass daisy-wheel, struck by an “electric hammer” to print Roman letters through carbon paper onto a moving paper tape. In 1841 Alexander Bain devised an electromagnetic printing telegraph machine, it used pulses of electricity created by rotating a dial over contact points to release and stop a type-wheel turned by weight-driven clockwork. The critical issue was to have the sending and receiving elements working synchronously. Bain attempted to achieve this using centrifugal governors to regulate the speed of the clockwork, it was patented, along with other devices, on April 21, 1841. By 1846, the Morse telegraph service was operational between Washington, D. C. and New York.
Royal Earl House patented his printing telegraph that same year. He linked two 28-key piano-style keyboards by wire; each piano key represented a letter of the alphabet and when pressed caused the corresponding letter to print at the receiving end. A "shift" key gave each main key two optional values. A 56-character typewheel at the sending end was synchronised to coincide with a similar wheel at the receiving end. If the key corresponding to a particular character was pressed at the home station, it actuated the typewheel at the distant station just as the same character moved into the printing position, in a way similar to the daisy wheel printer, it was thus an example of a synchronous data transmission system. House's equipment could transmit around 40 readable words per minute, but was difficult to manufacture in bulk; the printer could print out up to 2,000 words per hour. This invention was first put in operation and exhibited at the Mechanics Institute in New York in 1844. Landline teleprinter operations began in 1849, when a circuit was put in service between Philadelphia and New York City.
In 1855, David Edward Hughes introduced an improved machine built on the work of Royal Earl House. In less than two years, a number of small telegraph companies, including Western Union in early stages of development, united to form one large corporation – Western Union Telegraph Co. – to carry on the business of telegraphy on the Hughes system. In France, Émile Baudot designed in 1874 a system using a five-unit code, which began to be used extensively in that country from 1877; the British Post Office adopted the Baudot system for use on a simplex circuit between London and Paris in 1897, subsequently made considerable use of duplex Baudot systems on their Inland Telegraph Services. During 1901, Baudot's code was modified by Donald Murray, prompted by his development of a typewriter-like keyboard; the Murray system employed an intermediate step, a keyboard perforator, which allowed an operator to punch a paper tape, a tape transmitter for sending the message from the punched tape. At the receiving end of the line, a printing mechanism would
Nokia Bell Labs is an industrial research and scientific development company owned by Finnish company Nokia. Its headquarters are located in New Jersey. Other laboratories are located around the world. Bell Labs has its origins in the complex past of the Bell System. In the late 19th century, the laboratory began as the Western Electric Engineering Department and was located at 463 West Street in New York City. In 1925, after years of conducting research and development under Western Electric, the Engineering Department was reformed into Bell Telephone Laboratories and under the shared ownership of American Telephone & Telegraph Company and Western Electric. Researchers working at Bell Labs are credited with the development of radio astronomy, the transistor, the laser, the photovoltaic cell, the charge-coupled device, information theory, the Unix operating system, the programming languages C, C++, S. Nine Nobel Prizes have been awarded for work completed at Bell Laboratories. In 1880, when the French government awarded Alexander Graham Bell the Volta Prize of 50,000 francs (approximately US$10,000 at that time for the invention of the telephone, he used the award to fund the Volta Laboratory in Washington, D.
C. in collaboration with Sumner Tainter and Bell's cousin Chichester Bell. The laboratory was variously known as the Volta Bureau, the Bell Carriage House, the Bell Laboratory and the Volta Laboratory, it focused on the analysis and transmission of sound. Bell used his considerable profits from the laboratory for further research and education to permit the " diffusion of knowledge relating to the deaf": resulting in the founding of the Volta Bureau, located at Bell's father's house at 1527 35th Street N. W. in Washington, D. C, its carriage house became their headquarters in 1889. In 1893, Bell constructed a new building close by at 1537 35th Street N. W. to house the lab. This building was declared a National Historic Landmark in 1972. After the invention of the telephone, Bell maintained a distant role with the Bell System as a whole, but continued to pursue his own personal research interests; the Bell Patent Association was formed by Alexander Graham Bell, Thomas Sanders, Gardiner Hubbard when filing the first patents for the telephone in 1876.
Bell Telephone Company, the first telephone company, was formed a year later. It became a part of the American Bell Telephone Company. American Telephone & Telegraph Company and its own subsidiary company, took control of American Bell and the Bell System by 1889. American Bell held a controlling interest in Western Electric whereas AT&T was doing research into the service providers. In 1884, the American Bell Telephone Company created the Mechanical Department from the Electrical and Patent Department formed a year earlier. In 1896, Western Electric bought property at 463 West Street to station their manufacturers and engineers, supplying AT&T with their product; this included everything from telephones, telephone exchange switches, transmission equipment. In 1925, Bell Laboratories was developed to better consolidate the research activities of the Bell System. Ownership was evenly split between Western Electric and AT&T. Throughout the next decade the AT&T Research and Development branch moved into West Street.
Bell Labs carried out consulting work for the Bell Telephone Company, U. S. government work, a few workers were assigned to basic research. The first president of research at Bell Labs was Frank B. Jewett who stayed there until 1940. By the early 1940s, Bell Labs engineers and scientists had begun to move to other locations away from the congestion and environmental distractions of New York City, in 1967 Bell Laboratories headquarters was relocated to Murray Hill, New Jersey. Among the Bell Laboratories locations in New Jersey were Holmdel, Crawford Hill, the Deal Test Site, Lincroft, Long Branch, Neptune, Piscataway, Red Bank and Whippany. Of these, Murray Hill and Crawford Hill remain in existence; the largest grouping of people in the company was in Illinois, at Naperville-Lisle, in the Chicago area, which had the largest concentration of employees prior to 2001. There were groups of employees in Indianapolis, Indiana. Since 2001, many of the former locations closed; the Holmdel site, a 1.9 million square foot structure set on 473 acres, was closed in 2007.
The mirrored-glass building was designed by Eero Saarinen. In August 2013, Somerset Development bought the building, intending to redevelop it into a mixed commercial and residential project. A 2012 article expressed doubt on the success of the newly named Bell Works site however several large tenants had announced plans to move in through 2016 and 2017 Bell Laboratories was, is, regarded by many as the premier research facility of its type, developing a wide range of revolutionary technologies, including radio astronomy, the transistor, the laser, information theory, the operating system Unix, the programming languages C and C++, solar cells, the CCD, floating-gate MOSFET, a whole host of optical and wired communications
Butler W. Lampson, ForMemRS, is an American computer scientist best known for his contributions to the development and implementation of distributed personal computing. After graduating from the Lawrenceville School, Lampson received an A. B. in physics from Harvard University in 1964 and a Ph. D. in electrical engineering and computer science from the University of California, Berkeley in 1967. During the 1960s, Lampson and others were part of Project GENIE at UC Berkeley. In 1965, several Project GENIE members Lampson and Peter Deutsch, developed the Berkeley Timesharing System for Scientific Data Systems' SDS 940 computer. After completing his doctorate, Lampson stayed on at UC Berkeley as an assistant professor and associate professor of computer science. For a period of time, he concurrently served as director of system development for the Berkeley Computer Corporation. In 1971, Lampson became one of the founding members of Xerox PARC, where he worked in the Computer Science Laboratory as a principal scientist and senior research fellow.
His now-famous vision of a personal computer was captured in the 1972 memo entitled "Why Alto?". In 1973, the Xerox Alto, with its three-button mouse and full-page-sized monitor, was born, it is now considered to be the first actual personal computer in terms of what has become the "canonical" GUI mode of operation. All the subsequent computers built at Xerox PARC except for the "Dolphin" and the "Dorado" followed a general blueprint called "Wildflower", written by Lampson, this included the D-Series Machines: the "Dandelion", "Dandetiger", "Daybreak", "Dicentra". At PARC, Lampson helped work on many other revolutionary technologies, such as laser printer design, he designed several influential programming languages such as Euclid. Following the acrimonious resignation of Xerox PARC CSL manager Bob Taylor in 1983, Lampson and Chuck Thacker followed their longtime colleague to Digital Equipment Corporation's Systems Research Center. There, he was a senior consulting engineer, corporate consulting engineer and senior corporate consulting engineer.
Shortly before Taylor's retirement, Lampson left to work for Microsoft Research as an architect, distinguished engineer and technical fellow. Since 1987, Lampson has been an adjunct professor of electrical engineering and computer science at the Massachusetts Institute of Technology. In 1984, he was elected to the National Academy of Engineering. In 1984, he won the ACM Software System Award for the Alto, along with Robert W. Taylor, Charles P. Thacker. In 1986, he received an honorary Sc. D. from the Eidgenössische Technische Hochschule, Zürich. In 1992, he won the prestigious ACM Turing Award for his contributions to personal computing and computer science. In 1993, he became a fellow of the American Academy of Sciences. In 1994, he was inducted as a Fellow of the ACM. In 1996, he received the IEEE Computer Pioneer Award. In 1996, he received an honorary Sc. D. from the University of Bologna. In 2001, he received the IEEE John von Neumann Medal. In 2004, he won the Charles Stark Draper Prize along with Alan C.
Kay, Robert W. Taylor, Charles P. Thacker for their work on Alto. In 2005, he was elected to the National Academy of Sciences. In 2006, he was inducted as a Fellow of the Computer History Museum "for fundamental contributions to computer science, including networked personal workstations, operating systems, computer security and document publishing." Computer History Museum Fellow In 2006, he received the IFIP TC11 Kristian Beckman Award for information security. In 2016, he was inducted into the National Cybersecurity Hall of Fame. In 2018, he was elected as a Foreign Member of the Royal Society. Lampson is quoted as saying, "Any problem in computer science can be solved with another level of indirection," but in his Turing Award Lecture in 1993, Lampson himself attributes this saying to David Wheeler. Lampson's website The milliLampson unit Butler Lampson. Oral history interview, 11 December 2014, Massachusetts. Charles Babbage Institute, University of Minnesota
Multics is an influential early time-sharing operating system, based on the concept of a single-level memory. All modern operating systems were influenced by Multics – through Unix, created by some of the people who had worked on Multics – either directly or indirectly. Initial planning and development for Multics started in Cambridge, Massachusetts, it was a cooperative project led by MIT along with General Electric and Bell Labs. It was developed on the GE 645 computer, specially designed for it. Multics was conceived as a commercial product for General Electric, became one for Honeywell, albeit not successfully. Due to its many novel and valuable ideas, Multics had a significant impact on computer science despite its faults. Multics had numerous features intended to ensure high availability so that it would support a computing utility similar to the telephone and electricity utilities. Modular hardware structure and software architecture were used to achieve this; the system could grow in size by adding more of the appropriate resource, be it computing power, main memory, or disk storage.
Separate access control lists on every file provided flexible information sharing, but complete privacy when needed. Multics had a number of standard mechanisms to allow engineers to analyze the performance of the system, as well as a number of adaptive performance optimization mechanisms. Multics implemented a single-level store for data access, discarding the clear distinction between files and process memory; the memory of a process consisted of segments that were mapped into its address space. To read or write to them, the process used normal central processing unit instructions, the operating system took care of making sure that all the modifications were saved to disk. In POSIX terminology, it was. All memory in the system was part of some segment. One disadvantage of this was that the size of segments was limited to 256 kilowords, just over 1 MiB; this was due to the particular hardware architecture of the machines on which Multics ran, having a 36-bit word size and index registers of half that size.
Extra code had to be used to work on files larger than this, called multisegment files. In the days when one megabyte of memory was prohibitively expensive, before large databases and huge bitmap graphics, this limit was encountered. Another major new idea of Multics was dynamic linking, in which a running process could request that other segments be added to its address space, segments which could contain code that it could execute; this allowed applications to automatically use the latest version of any external routine they called, since those routines were kept in other segments, which were dynamically linked only when a process first tried to begin execution in them. Since different processes could use different search rules, different users could end up using different versions of external routines automatically. With the appropriate settings on the Multics security facilities, the code in the other segment could gain access to data structures maintained in a different process. Thus, to interact with an application running in part as a daemon, a user's process performed a normal procedure-call instruction to a code segment to which it had dynamically linked.
The code in that segment could modify data maintained and used in the daemon. When the action necessary to commence the request was completed, a simple procedure return instruction returned control of the user's process to the user's code; the single-level store and dynamic linking are still not available to their full power in other used operating systems, despite the rapid and enormous advance in the computer field since the 1960s. They are becoming more accepted and available in more limited forms, for example, dynamic linking. Multics supported aggressive on-line reconfiguration: central processing units, memory banks, disk drives, etc. could be added and removed while the system continued operating. At the MIT system, where most early software development was done, it was common practice to split the multiprocessor system into two separate systems during off-hours by incrementally removing enough components to form a second working system, leaving the rest still running the original logged-in users.
System software development testing could be done on the second system the components of the second system were added back to the main user system, without having shut it down. Multics supported multiple CPUs. Multics was the first major operating system. Despite this, early versions of Multics were broken into repeatedly; this led to further work that made the system much more secure and prefigured modern security engineering techniques. Break-ins became rare once the second-generation hardware base was adopted. Multics was the first operating system to provide a hierarchical file system, file names could be of alm
A regular expression, regex or regexp is a sequence of characters that define a search pattern. This pattern is used by string searching algorithms for "find" or "find and replace" operations on strings, or for input validation, it is a technique developed in formal language theory. The concept arose in the 1950s when the American mathematician Stephen Cole Kleene formalized the description of a regular language; the concept came into common use with Unix text-processing utilities. Since the 1980s, different syntaxes for writing regular expressions exist, one being the POSIX standard and another used, being the Perl syntax. Regular expressions are used in search engines and replace dialogs of word processors and text editors, in text processing utilities such as sed and AWK and in lexical analysis. Many programming languages provide regex capabilities, built-in or via libraries; the phrase regular expressions, regexes, is used to mean the specific, standard textual syntax for representing patterns for matching text.
Each character in a regular expression is either a metacharacter, having a special meaning, or a regular character that has a literal meaning. For example, in the regex a. A is a literal character which matches just'a', while'.' is a meta character that matches every character except a newline. Therefore, this regex matches, for example,'a', or'ax', or'a0'. Together and literal characters can be used to identify text of a given pattern, or process a number of instances of it. Pattern matches may vary from a precise equality to a general similarity, as controlled by the metacharacters. For example. Is a general pattern, is less general and a is a precise pattern; the metacharacter syntax is designed to represent prescribed targets in a concise and flexible way to direct the automation of text processing of a variety of input data, in a form easy to type using a standard ASCII keyboard. A simple case of a regular expression in this syntax is to locate a word spelled two different ways in a text editor, the regular expression serialie matches both "serialise" and "serialize".
Wildcards achieve this, but are more limited in what they can pattern, as they have fewer metacharacters and a simple language-base. The usual context of wildcard characters is in globbing similar names in a list of files, whereas regexes are employed in applications that pattern-match text strings in general. For example, the regex ^+|+$ matches excess whitespace at the beginning or end of a line. An advanced regular expression that matches any numeral is??. A regex processor translates a regular expression in the above syntax into an internal representation which can be executed and matched against a string representing the text being searched in. One possible approach is the Thompson's construction algorithm to construct a nondeterministic finite automaton, made deterministic and the resulting deterministic finite automaton is run on the target text string to recognize substrings that match the regular expression; the picture shows the NFA scheme N obtained from the regular expression s*, where s denotes a simpler regular expression in turn, recursively translated to the NFA N.
Regular expressions originated in 1951, when mathematician Stephen Cole Kleene described regular languages using his mathematical notation called regular sets. These arose in theoretical computer science, in the subfields of automata theory and the description and classification of formal languages. Other early implementations of pattern matching include the SNOBOL language, which did not use regular expressions, but instead its own pattern matching constructs. Regular expressions entered popular use from 1968 in two uses: pattern matching in a text editor and lexical analysis in a compiler. Among the first appearances of regular expressions in program form was when Ken Thompson built Kleene's notation into the editor QED as a means to match patterns in text files. For speed, Thompson implemented regular expression matching by just-in-time compilation to IBM 7094 code on the Compatible Time-Sharing System, an important early example of JIT compilation, he added this capability to the Unix editor ed, which led to the popular search tool grep's use of regular expressions.
Around the same time when Thompson developed QED, a group of researchers including Douglas T. Ross implemented a tool based on regular expressions, used for lexical analysis in compiler design. Many variations of these original forms of regular expressions were used in Unix programs at Bell Labs in the 1970s, including vi, sed, AWK, expr, in other programs such as Emacs. Regexes were subsequently adopted by a wide range of programs, with these early forms standardized in the POSIX.2 standard in 1992. In the 1980s the more complicated regexes arose in Perl, which derived from a regex library written by Henry Spencer, who wrote an implementation of Advanced Regular Expressions for Tcl; the Tcl library is a hybrid NFA/DFA implementation with improved performance characteristics. Software projects that have adopted Spencer's Tcl regular expression implementation include PostgreSQL. Perl expanded on Spencer's original library
Brian Wilson Kernighan is a Canadian computer scientist. He worked at Bell Labs and contributed to the development of Unix alongside Unix creators Ken Thompson and Dennis Ritchie. Kernighan's name became known through co-authorship of the first book on the C programming language with Dennis Ritchie. Kernighan affirmed, he authored many Unix programs, including ditroff. Kernighan is coauthor of the AMPL programming languages; the "K" of K&R C and the "K" in AWK both stand for "Kernighan". In collaboration with Shen Lin he devised well-known heuristics for two NP-complete optimization problems: graph partitioning and the travelling salesman problem. In a display of authorial equity, the former is called the Kernighan–Lin algorithm, while the latter is known as the Lin–Kernighan heuristic. Kernighan has been a Professor in the Computer Science Department of Princeton University since 2000, he is the Undergraduate Department Representative. Kernighan was born in Toronto, he attended the University of Toronto between 1960 and 1964, earning his Bachelor's degree in engineering physics.
He received his PhD in electrical engineering from Princeton University in 1969 for research supervised by Peter Weiner. Kernighan has held a professorship in the Department of Computer Science at Princeton since 2000; each fall he teaches a course called "Computers in Our World", which introduces the fundamentals of computing to non-majors. Kernighan was the software editor for Prentice Hall International, his "Software Tools" series spread the essence of "C/Unix thinking" with makeovers for BASIC, FORTRAN, Pascal, most notably his "Ratfor" was put in the public domain. He has said that if stranded on an island with only one programming language it would have to be C. Kernighan coined the term helped popularize Thompson's Unix philosophy. Kernighan is known as a coiner of the expression "What You See Is All You Get", a sarcastic variant of the original "What You See Is What You Get". Kernighan's term is used to indicate that WYSIWYG systems might throw away information in a document that could be useful in other contexts.
Kernighan's original 1978 implementation of Hello, World! was sold at The Algorithm Auction, the world's first auction of computer algorithms. In 1996, Kernighan taught CS50, the Harvard University introductory course in Computer Science. Other achievements during his career include: Brian Kernighan's home page at Bell Labs "Why Pascal is Not My Favorite Programming Language" — By Brian Kernighan, AT&T Bell Labs, 2 April 1981 "Leap In and Try Things" — Interview with Brian Kernighan — on "Harmony at Work Blog", October 2009. An Interview with Brian Kernighan — By Mihai Budiu, for PC Report Romania, August 2000 "Transcript of an interview with Brian Kernighan". Archived from the original on 2009-04-28. Retrieved 2016-03-31. – Interview by"Michael S. Mahoney". Archived from the original on 2009-05-28. Retrieved 2016-03-31. Video — TechNetCast At Bell Labs: Dennis Ritchie and Brian Kernighan Video — "Assembly for the Class of 2007:'D is for Digital and Why It Matters'" A Descent into Limbo by Brian Kernighan Photos of Brian Kernighan Works by Brian Kernighan at Open Library Video interview with Brian Kernighan for Princeton Startup TV The Setup, Brian Kernighan
The cathode-ray tube is a vacuum tube that contains one or more electron guns and a phosphorescent screen, is used to display images. It modulates and deflects electron beam onto the screen to create the images; the images may represent electrical waveforms, radar targets, or other phenomena. CRTs have been used as memory devices, in which case the visible light emitted from the fluorescent material is not intended to have significant meaning to a visual observer. In television sets and computer monitors, the entire front area of the tube is scanned repetitively and systematically in a fixed pattern called a raster. An image is produced by controlling the intensity of each of the three electron beams, one for each additive primary color with a video signal as a reference. In all modern CRT monitors and televisions, the beams are bent by magnetic deflection, a varying magnetic field generated by coils and driven by electronic circuits around the neck of the tube, although electrostatic deflection is used in oscilloscopes, a type of electronic test instrument.
A CRT is constructed from a glass envelope, large, deep heavy, fragile. The interior of a CRT is evacuated to 0.01 pascals to 133 nanopascals, evacuation being necessary to facilitate the free flight of electrons from the gun to the tube's face. The fact that it is evacuated makes handling an intact CRT dangerous due to the risk of breaking the tube and causing a violent implosion that can hurl shards of glass at great velocity; as a matter of safety, the face is made of thick lead glass so as to be shatter-resistant and to block most X-ray emissions if the CRT is used in a consumer product. Since the late 2000s, CRTs have been superseded by newer "flat panel" display technologies such as LCD, plasma display, OLED displays, which in the case of LCD and OLED displays have lower manufacturing costs and power consumption, as well as less weight and bulk. Flat panel displays can be made in large sizes. Cathode rays were discovered by Johann Wilhelm Hittorf in 1869 in primitive Crookes tubes, he observed that some unknown rays were emitted from the cathode which could cast shadows on the glowing wall of the tube, indicating the rays were traveling in straight lines.
In 1890, Arthur Schuster demonstrated cathode rays could be deflected by electric fields, William Crookes showed they could be deflected by magnetic fields. In 1897, J. J. Thomson succeeded in measuring the mass of cathode rays, showing that they consisted of negatively charged particles smaller than atoms, the first "subatomic particles", which were named electrons; the earliest version of the CRT was known as the "Braun tube", invented by the German physicist Ferdinand Braun in 1897. It was a modification of the Crookes tube with a phosphor-coated screen; the first cathode-ray tube to use a hot cathode was developed by John B. Johnson and Harry Weiner Weinhart of Western Electric, became a commercial product in 1922. In 1925, Kenjiro Takayanagi demonstrated a CRT television that received images with a 40-line resolution. By 1927, he improved the resolution to 100 lines, unrivaled until 1931. By 1928, he was the first to transmit human faces in half-tones on a CRT display. By 1935, he had invented an early all-electronic CRT television.
It was named in 1929 by inventor Vladimir K. Zworykin, influenced by Takayanagi's earlier work. RCA was granted a trademark for the term in 1932; the first commercially made electronic television sets with cathode-ray tubes were manufactured by Telefunken in Germany in 1934. Flat panel displays dropped in price and started displacing cathode-ray tubes in the 2000s, with LCD screens exceeding CRTs in 2008; the last known manufacturer of CRTs ceased in 2015. In oscilloscope CRTs, electrostatic deflection is used, rather than the magnetic deflection used with television and other large CRTs; the beam is deflected horizontally by applying an electric field between a pair of plates to its left and right, vertically by applying an electric field to plates above and below. Televisions use magnetic rather than electrostatic deflection because the deflection plates obstruct the beam when the deflection angle is as large as is required for tubes that are short for their size. Various phosphors are available depending upon the needs of the display application.
The brightness and persistence of the illumination depends upon the type of phosphor used on the CRT screen. Phosphors are available with persistences ranging from less than one microsecond to several seconds. For visual observation of brief transient events, a long persistence phosphor may be desirable. For events which are fast and repetitive, or high frequency, a short-persistence phosphor is preferable; when displaying fast one-shot events, the electron beam must deflect quickly, with few electrons impinging on the screen, leading to a faint or invisible image on the display. Oscilloscope CRTs designed for fast signals can give a brighter display by passing the electron beam through a micro-channel plate just before it reaches