Most digital computers built in this period were electromechanical – electric switches drove mechanical relays to perform the calculation. The Astronomical Computing Bureau, Columbia University, performed astronomical calculations representing the state of the art in computing. B. in der Klimaforschung oder für medizinische Berechnungen. The Lorenz SZ 40/42 machine was used for high-level Army communications, code-named "Tunny" by the British. The other contender for being the first recognizably modern digital stored-program computer was the EDSAC, designed and constructed by Maurice Wilkes and his team at the University of Cambridge Mathematical Laboratory in England at the University of Cambridge in 1949. The integrated circuit in the image on the right, for example, an Intel 8742, is an 8-bit microcontroller that includes a CPU running at 12 MHz, 128 bytes of RAM, 2048 bytes of EPROM, and I/O in the same chip. The development of transistor technology and then the integrated circuit chip led to a series of breakthroughs, starting with transistor computers and then integrated circuit computers, causing digital computers to largely replace analog computers. By the simple strategy of never shutting down ENIAC, the failures were dramatically reduced. As a result, the machines were not included in many histories of computing. It also had modules to multiply, divide, and square root.  To process these punched cards, he invented the tabulator and the keypunch machine. Battle posted his first youtube video in 2013, the channel began as an outlet for his band at the time ZIBRA and his own creations, he tells Red Bull in an intervie… The Experimental machine led on to the development of the Manchester Mark 1 at the University of Manchester. There were three separate readers for the three types of cards. Many second-generation CPUs delegated peripheral device communications to a secondary processor. In these machines, the basic unit of data was the decimal digit, encoded in one of several schemes, including binary-coded decimal or BCD, bi-quinary, excess-3, and two-out-of-five code. Details of their existence, design, and use were kept secret well into the 1970s. In 1951, British scientist Maurice Wilkes developed the concept of microprogramming from the realisation that the central processing unit of a computer could be controlled by a miniature, highly specialised computer program in high-speed ROM. B. eine Logarithmentafel füllten. In two 1936 patent applications, Zuse also anticipated that machine instructions could be stored in the same storage used for data—the key insight of what became known as the von Neumann architecture, first implemented in 1948 in America in the electromechanical IBM SSEC and in Britain in the fully electronic Manchester Baby.. " However, Leibniz did not incorporate a fully successful carry mechanism.  Content-addressable memory (CAM) has become inexpensive enough to be used in networking, and is frequently used for on-chip cache memory in modern microprocessors, although no computer system has yet implemented hardware CAMs for use in programming languages. All the parts for his machine had to be made by hand—this was a major problem for a machine with thousands of parts. Purely electronic circuit elements soon replaced their mechanical and electromechanical equivalents, at the same time that digital calculation replaced analog. These included the astrolabe and Antikythera mechanism from the Hellenistic world (c. 150–100 BC). During the second generation remote terminal units (often in the form of Teleprinters like a Friden Flexowriter) saw greatly increased use. These devices used the continuously changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved, in contrast to digital computers that represented varying quantities symbolically, as their numerical values change. , Noyce came up with his own idea of an integrated circuit half a year after Kilby. This appears to be the first published description of programming, so Ada Lovelace is widely regarded as the first computer programmer. , An indication of the rapidity of development of this field can be inferred from the history of the seminal 1947 article by Burks, Goldstine and von Neumann. Der Journalist Steven Levy veröffentlichte 1984 das weltweit erste Buch, das sich unter anderem mit der frühen Geschichte des Personal Computers auseinandersetzt und dabei die Entwickler und deren Motivation in den Mittelpunkt stellt. In 1804, French weaver Joseph Marie Jacquard developed a loom in which the pattern being woven was controlled by a paper tape constructed from punched cards.  It used vacuum tubes, cold-cathode tubes and Dekatrons in its circuits, with 12 cold-cathode "Nixie" tubes for its display. Dummer.  A Google team has succeeded in operating their RF pulse modulator chip at 3 Kelvin, simplifying the cryogenics of their 72-qubit computer, which is setup to operate at 0.3 Kelvin; but the readout circuitry and another driver remain to be brought into the cryogenics. Its primary storage was serial-access mercury delay lines capable of storing 1,000 words of 11 decimal digits plus sign (72-bit words). The IBM 704 (1955) and the Ferranti Mercury (1957) used magnetic-core memory. (Later drawings depict a regularized grid layout. Although substantially similar to Turing's design and containing comparatively little engineering detail, the computer architecture it outlined became known as the "von Neumann architecture". In the same year, electro-mechanical devices called bombes were built by British cryptologists to help decipher German Enigma-machine-encrypted secret messages during World War II. These devices had a low operating speed and were eventually superseded by much faster all-electric computers, originally using vacuum tubes.  Ramon Llull invented the Lullian Circle: a notional machine for calculating answers to philosophical questions (in this case, to do with Christianity) via logical combinatorics.  They showed that electronic relays and switches can realize the expressions of Boolean algebra. Weiterhin können Daten-Schreiboperationen in der Harvard-Architektur keine Programme überschreiben (Informationssicherheit). 650 Magnetic Drum Calculator —Case 20878" Bell Telephone Laboratories Technical Memorandum MM-114-37, Reported in IBM Technical Newsletter No.  By the 1920s, British scientist Lewis Fry Richardson's interest in weather prediction led him to propose human computers and numerical analysis to model the weather; to this day, the most powerful computers on Earth are needed to adequately model its weather using the Navier–Stokes equations.. Auf der untersten Ebene findet sich aber immer der so genannte Maschinencode – jene Abfolge von Zahlen, mit der der Computer auch tatsächlich gesteuert wird.  Tommy Flowers, a senior engineer at the Post Office Research Station was recommended to Max Newman by Alan Turing and spent eleven months from early February 1943 designing and building the more flexible Colossus computer (which superseded the Heath Robinson). The machine was huge, weighing 30 tons, using 200 kilowatts of electric power and contained over 18,000 vacuum tubes, 1,500 relays, and hundreds of thousands of resistors, capacitors, and inductors. While working at the research station in Dollis Hill in the 1930s, he began to explore the possible use of electronics for the telephone exchange. The "third-generation" of digital electronic computers used integrated circuit (IC) chips as the basis of their logic. Pre-assembled systems did not gain much ground until 1977, with the introduction of the Apple II, the Tandy TRS-80, the first SWTPC computers, and the Commodore PET. The history of computing hardware covers the developments from early simple devices to aid calculation to modern day computers.  Women often operated these bombe machines. Colossus Mark 1 contained 1500 thermionic valves (tubes), but Mark 2 with 2400 valves and five processors in parallel, was both 5 times faster and simpler to operate than Mark 1, greatly speeding the decoding process. The programmers of the ENIAC were women who had been trained as mathematicians.. The microprocessor has origins in the MOS integrated circuit (MOS IC) chip. In the US, a series of computers at Control Data Corporation (CDC) were designed by Seymour Cray to use innovative designs and parallelism to achieve superior computational peak performance.  Edmund Gunter built a calculating device with a single logarithmic scale at the University of Oxford. It was built at the Victoria University of Manchester by Frederic C. Williams, Tom Kilburn and Geoff Tootill, and ran its first program on 21 June 1948.. Basic Tutorials.  The first single-chip microprocessor was the Intel 4004, developed on a single PMOS LSI chip. Considered the "father of the computer", he conceptualized and invented the first mechanical computer in the early 19th century. His device was the foundation for further developments in analog computing.. Most of the use of Colossus was in determining the start positions of the Tunny rotors for a message, which was called "wheel setting". Sept. 2, 2020. , Following Babbage, although unaware of his earlier work, was Percy Ludgate, a clerk to a corn merchant in Dublin, Ireland.  In 1967, Dawon Kahng and Simon Sze at Bell Labs developed the floating-gate MOSFET, the basis for MOS non-volatile memory such as EPROM, EEPROM and flash memory. A dozen of these devices were built before their obsolescence became obvious; the most powerful was constructed at the University of Pennsylvania's Moore School of Electrical Engineering, where the ENIAC was built. Memory limitations such as this were to dominate programming for decades afterward. Most possibilities led to a contradiction, and the few remaining could be tested by hand. Although this approach generally required more complex mechanisms, it greatly increased the precision of results. Zum Typus des derzeit meistverbreiteten Computers siehe, Weltweite Marktanteile der Computerhersteller, Folgende Teile dieses Abschnitts scheinen seit 2012. A NeXT Computer and its object-oriented development tools and libraries were used by Tim Berners-Lee and Robert Cailliau at CERN to develop the world's first web server software, CERN httpd, and also used to write the first web browser, WorldWideWeb. Here is the ChangeLog of this history.. Geschichte des Computer Der erste Computer Der erste Computer (Z3) wurde von Konrad Zuse erfunden.Er lebte von 22.juni 1910 bis 18.dezember 1995.Es folgte kurz darauf der Z4.Das Z beim Z3/4 bedeutet Zuse. [n] IBM implemented its IBM Solid Logic Technology modules in hybrid circuits for the IBM System/360 in 1964. Computers can be connected together to form networks, allowing connected computers to … Diese folgen gemeinsamen Grundprinzipien, mit denen ihre freie Programmierung ermöglicht wird. Mögliche Einsatzmöglichkeiten für Computer sind: Das heute allgemein angewandte Prinzip, das nach seiner Beschreibung durch John von Neumann von 1946 als Von-Neumann-Architektur bezeichnet wird, definiert für einen Computer fünf Hauptkomponenten: In den heutigen Computern sind die ALU und die Steuereinheit meistens zu einem Baustein verschmolzen, der so genannten CPU (Central Processing Unit, zentraler Prozessor). By the 1950s the success of digital electronic computers had spelled the end for most analog computing machines, but hybrid analog computers, controlled by digital electronics, remained in substantial use into the 1950s and 1960s, and later in some specialized applications. Leibniz also described the binary numeral system, a central ingredient of all modern computers. Computer science is the study of algorithmic processes and computational machines.  A continuing debate exists over whether Schickard or Pascal should be regarded as the "inventor of the mechanical calculator" and the range of issues to be considered is discussed elsewhere.  Hollerith's method was used in the 1890 United States Census. OpenComputers is a mod by Sangar which adds Lua-based programmable computers and robots.  It was a second-generation machine, using discrete germanium transistors.  Six Metrovick 950s were built, the first completed in 1956. While producing the first logarithmic tables, Napier needed to perform many tedious multiplications.  It was used by the Imperial Russian Navy in World War I. When the United States instituted Social Security in 1935, IBM punched-card systems were used to process records of 26 million workers. Early mechanical tools to help humans with digital calculations, like the abacus, were referred to as calculating machines or calculators (and other proprietary names). Remington Rand eventually sold 46 machines at more than US$1 million each ($9.85 million as of 2020).  See: Quantum supremacy Silicon qubit systems have demonstrated entanglement at non-local distances. Sie bekommt die Werte von der Steuereinheit geliefert, verrechnet sie (addiert beispielsweise zwei Zahlen) und gibt den Wert an die Steuereinheit zurück, die den Wert dann für einen Vergleich verwenden oder in eine andere Speicherzelle schreiben kann. Experimental equipment that he built in 1934 went into operation 5 years later, converting a portion of the telephone exchange network into an electronic data processing system, using thousands of vacuum tubes. 500 € vergleichbare Leistung. Blog. It was a substantial development from a device that had been designed in 1938 by Polish Cipher Bureau cryptologist Marian Rejewski, and known as the "cryptologic bomb" (Polish: "bomba kryptologiczna").  This concept greatly simplified CPU development. B. für die Astronomie, für die Geodäsie oder für die Ballistik) im Auftrag von Mathematikern ausführten und damit Tabellen wie z. Ein Digitalrechner besteht zunächst nur aus Hardware. Semiconductor memory, also known as MOS memory, was cheaper and consumed less power than magnetic-core memory.  Typically signals have two states – low (usually representing 0) and high (usually representing 1), but sometimes three-valued logic is used, especially in high-density memory. Seit 1962 ist der Begriff in Deutschland belegt.. Turing presented a more detailed paper to the National Physical Laboratory (NPL) Executive Committee in 1946, giving the first reasonably complete design of a stored-program computer, a device he called the Automatic Computing Engine (ACE). elektrischen Hilfsmitteln (Rechenmaschinen oder Hardware). Odra 1003, 1013, 1103, 1204 i tranzystorowy arytmometr ELWRO TMK: Józef THIERRY , Maszyny matematyczne ODRA.  In 1879 Gottlob Frege develops the formal approach to logic and proposes the first logic language for logical equations.. Apparently his work remained largely unknown to engineers in the UK and US until much later, although at least IBM was aware of it as it financed his post-war startup company in 1946 in return for an option on Zuse's patents. ERA, then a part of Univac included a drum memory in its 1103, announced in February 1953. On 17 November 1951, the J. Lyons company began weekly operation of a bakery valuations job on the LEO (Lyons Electronic Office). Diese Rechenleistung haben Supercomputer bereits deutlich überschritten. It combined the high speed of electronics with the ability to be programmed for many complex problems. With performance of about 1 megaFLOPS, the CDC 6600 was the world's fastest computer from 1964 to 1969, when it relinquished that status to its successor, the CDC 7600. Although a vacuum tube might fail, it would be replaced without bringing down the system. It was quite similar to modern machines in some respects, pioneering numerous advances such as floating point numbers. The machine was inspired by John von Neumann's seminal First Draft of a Report on the EDVAC and was one of the first usefully operational electronic digital stored-program computer.  In addition to data processing, the MOSFET enabled the practical use of MOS transistors as memory cell storage elements, a function previously served by magnetic cores. Next to the fixed disk storage units, connected to the CPU via high-speed data transmission, were removable disk data storage units. This was the first business application to go live on a stored program computer.[h]. Colossus was the world's first electronic digital programmable computer. As a complete system, this was a significant step from the Altair, though it never achieved the same success. As it was designed to be the simplest possible stored-program computer, the only arithmetic operations implemented in hardware were subtraction and negation; other arithmetic operations were implemented in software. , Gottfried Wilhelm von Leibniz invented the stepped reckoner and his famous stepped drum mechanism around 1672. It had one or two 8" floppy disk drives, a 32-character plasma display, 80-column graphical thermal printer, 48 Kbytes of RAM, and BASIC language. His 1945 report ‘Proposed Electronic Calculator’ was the first specification for such a device. , It was widely used in the CPUs and floating-point units of mainframe and other computers; it was implemented for the first time in EDSAC 2, which also used multiple identical "bit slices" to simplify design.  In a differential analyzer, the output of one integrator drove the input of the next integrator, or a graphing output. Komputer osobisty (ang.personal computer, PC) – komputer ogólnego przeznaczenia którego rozmiar, możliwości i cena predysponują go do indywidualnego użytku.Komputery osobiste są obsługiwane bezpośrednio przez użytkownika końcowego, a nie przez technika lub innego specjalistę.Typowo jest używany przez jedną osobę. , Wikipedia:WikiProjekt Ereignisse/Vergangenheit/2012, Verkaufszahlen und Marktanteile der Computerhersteller nach Angaben des Marktforschungsunternehmens Gartner Inc., basierend auf Verkaufszahlen von Desktop-Computer, Notebooks, Netbooks, aber ohne Tabletcomputer, an Endkonsumenten:, Dieser Artikel erläutert Grundlagen aller Computer. Diese Berechnungen erfolgten größtenteils von Hand. Magnetic drum memories were developed for the US Navy during WW II with the work continuing at Engineering Research Associates (ERA) in 1946 and 1947. all wikis wikipedia only people's wikis only encyclopedias only add a wiki search within your own wiki contact wiki.com Around 1820, Charles Xavier Thomas de Colmar created what would over the rest of the century become the first successful, mass-produced mechanical calculator, the Thomas Arithmometer. Slide rules and nomograms are the simplest, while naval gunfire control computers and large hybrid digital/analog computers were among the most complicated. The tube technology was superseded in June 1963 by the U.S. manufactured Friden EC-130, which had an all-transistor design, a stack of four 13-digit numbers displayed on a 5-inch (13 cm) CRT, and introduced reverse Polish notation (RPN). • Konrad Zuse: Der Computer – Mein Lebenswerk. The castle clock, a hydropowered mechanical astronomical clock invented by Ismail al-Jazari in 1206, was the first programmable analog computer. The programming language to be employed by users was akin to modern day assembly languages. Zur Etymologie siehe Rechnen#Etymologie.  The MOS IC was first proposed by Mohamed M. Atalla at Bell Labs in 1960, and then fabricated by Fred Heiman and Steven Hofstein at RCA in 1962. A removable disk pack can be easily exchanged with another pack in a few seconds. die einen einzelnen voll funktionstüchtigen Rechner in ihrem Zusammenspiel bedingende Gesamtheit von externen und internen Komponenten, d. h. Diese Seite wurde zuletzt am 23. Initially the only devices available were germanium point-contact transistors, less reliable than the valves they replaced but which consumed far less power. However, up to the 1940s, many subsequent designs (including Charles Babbage's machines of the 1822 and even ENIAC of 1945) were based on the decimal system.[e]. Microcomputers, the first of which appeared in the 1970s, became ubiquitous in the 1980s and beyond. After working on his revolutionary difference engine, designed to aid in navigational calculations, in 1833 he realized that a much more general design, an Analytical Engine, was possible. Die Bibliotheken wurden in übergeordneten Bibliotheken gebündelt, welche Unterfunktionen zu komplexen Operationen verknüpfen (Beispiel: die Anzeige eines Buchstabens „A“, bestehend aus 20 einzelnen schwarzen und 50 einzelnen weißen Punkten auf dem Bildschirm, nachdem der Benutzer die Taste „A“ gedrückt hat).  Turing machines are to this day a central object of study in theory of computation. Except for the limitations imposed by their finite memory stores, modern computers are said to be Turing-complete, which is to say, they have algorithm execution capability equivalent to a universal Turing machine. Analogrechner funktionieren nach einem anderen Prinzip. The Baby had a 32-bit word length and a memory of 32 words. After 1945, others read John von Neumann's First Draft of a Report on the EDVAC, and immediately started implementing their own systems. Today, the requirement of reliable performance is made even more stringent when server farms are the delivery platform. The paper tape could be changed without changing the mechanical design of the loom. Metal-oxide-semiconductor (MOS) large-scale integration (LSI) then enabled semiconductor memory and the microprocessor, leading to another key breakthrough, the miniaturized personal computer (PC), in the 1970s. By 1953 this team had transistor circuits operating to read and write on a smaller magnetic drum from the Royal Radar Establishment.  Nine Pascalines have survived, most of which are on display in European museums. It had paper-tape input and was capable of being configured to perform a variety of boolean logical operations on its data, but it was not Turing-complete. Ein Megatrend sind derzeit (2017) die Entwicklung künstlicher Intelligenz. During the 1980s, CMOS logic gates developed into devices that could be made as fast as other circuit types; computer power consumption could therefore be decreased dramatically. Slide rules were used by generations of engineers and other mathematically involved professional workers, until the invention of the pocket calculator.. Hot-pluggable hard disks, like the hot-pluggable vacuum tubes of yesteryear, continue the tradition of repair during continuous operation. the central processing unit, of a computer, their progressive development naturally led to chips containing most or all of the internal electronic parts of a computer. Demgegenüber stehen in der Harvard-Architektur Daten und Programmen eigene (physikalisch getrennte) Speicherbereiche zur Verfügung. A computer is a machine that can be instructed to carry out sequences of arithmetic or logical operations automatically via computer programming.Modern computers have the ability to follow generalized sets of operations, called programs. Both models were programmable using switches and plug panels in a way their predecessors had not been. Der Zugriff auf die Speicherbereiche kann parallel realisiert werden, was zu Geschwindigkeitsvorteilen führt. The German encryption machine, Enigma, was first attacked with the help of the electro-mechanical bombes. Steuerung von Maschinen und Abläufen (Drucker, Produktion in der Industrie durch z.  Invented by Freddie Williams and Tom Kilburn at the University of Manchester in 1946 and 1947, it was a cathode ray tube that used an effect called secondary emission to temporarily store electronic binary data, and was used successfully in several early computers. veralteten, synonym gebrauchten Begriffe Rechenanlage, Datenverarbeitungsanlage oder elektronische Datenverarbeitungsanlage sowie Elektronengehirn anzutreffen. The first aids to computation were purely mechanical devices which required the operator to set up the initial values of an elementary arithmetic operation, then manipulate the device to obtain the result. Bei einem Digitalrechner werden dabei zwei grundsätzliche Bestandteile unterschieden: Die Hardware, die aus den elektronischen, physisch anfassbaren Teilen des Computers gebildet wird, sowie die Software, die die Programmierung des Computers beschreibt. w zakresie testów technicznych i analiz projektów realizowanych komputerowo. The Manchester Baby was the world's first electronic stored-program computer. This was a landmark achievement in programmability. That distinction goes to the Harwell CADET of 1955, built by the electronics division of the Atomic Energy Research Establishment at Harwell. W roku 1979 zaprojektował go William Moggridge dla Grid Systems Corporation. Because it made use of a single-tooth gear there were circumstances in which its carry mechanism would jam. The MOSFET (metal-oxide-semiconductor field-effect transistor, or MOS transistor) was invented by Mohamed M. Atalla and Dawon Kahng at Bell Labs in 1959. Przegląd produkcji zakładów ELWRO w zakresie maszyn cyfrowych, „Maszyny Matematyczne” (1), BIBLIOTEKA CYFROWA POLITECHNIKI ŚLĄSKIEJ, 1967, s. 20-23 [dostęp 2019-02-25] (pol.)..  Stored-program computers, by contrast, were designed to store a set of instructions (a program), in memory – typically the same memory as stored data. [b][c] The use of counting rods is one example. Early mechanical tools to help humans with digital calculations, like the abacus, were referred to as calculating machines or calculators (and other proprietary names).  This calculating device was fully electronic – control, calculations and output (the first electronic display). In 1944, the Harvard Mark I was constructed at IBM's Endicott laboratories. Geschichte des Computers Quellen: Lehrbuch Wikipedia Google Bilder YouTube Wissenschaft Informatik Grundlagen: Algorithmusbegriff und Automatentheorie Rechentechnik und Mikroelektronik Nachrichtentechnik und Informationstheorie Konrad Zuse Bauingenieur, Erfinder und Unternehmer  After a functional test in December 1943, Colossus was shipped to Bletchley Park, where it was delivered on 18 January 1944 and attacked its first message on 5 February.. The first of three programs written for the machine found the highest proper divisor of 218 (262,144), a calculation that was known would take a long time to run—and so prove the computer's reliability—by testing every integer from 218 − 1 downwards, as division was implemented by repeated subtraction of the divisor. Komplexere Aufgaben werden in Unteraufgaben zerlegt, die von anderen Programmierern bereits bearbeitet wurden, die wiederum auf die Vorarbeit weiterer Programmierer aufbauen, deren Bibliotheken sie verwenden. Companies like Friden, Marchant Calculator and Monroe made desktop mechanical calculators from the 1930s that could add, subtract, multiply and divide. Apple Inc. (dawniej Apple Computer Inc.) – amerykańskie przedsiębiorstwo informatyczne z siedzibą w Cupertino w Kalifornii. Thus many instructions were, when needed, located in the next row of the drum to be read and additional wait time for drum rotation was not required. Konrad Zuse (Z3, 1941 und Z4, 1945) in Berlin, John Presper Eckert und John William Mauchly (ENIAC, 1946) bauten die ersten funktionstüchtigen Geräte dieser Art. Transistorized electronics improved not only the CPU (Central Processing Unit), but also the peripheral devices. Jahrhunderts nicht wesentlich verändert, wenngleich die Details der Technologie erheblich verbessert wurden. Diese Information wird als Binärzahl, also eine Abfolge von ja/nein-Informationen im Sinne von Einsen und Nullen, in der Speicherzelle abgelegt. Die Von-Neumann-Architektur ist gewissermaßen die unterste Ebene des Funktionsprinzips eines Computers oberhalb der elektrophysikalischen Vorgänge in den Leiterbahnen. High-speed memory was limited to 20 words (equivalent to about 80 bytes). This thesis essentially founded practical digital circuit design. IBM introduced a smaller, more affordable computer in 1954 that proved very popular. Unlike the continuous current draw of a gate based on other logic types, a CMOS gate only draws significant current during the 'transition' between logic states, except for leakage.  Vier Jahre später (Dezember 2020) besitzen bereits Videospielkonsolen für ca. , The engineer Tommy Flowers joined the telecommunications branch of the General Post Office in 1926. Loops and conditional branching were possible, and so the language as conceived would have been Turing-complete as later defined by Alan Turing. Pierwszym oferowanym komercyjnie laptopem, który mieścił się w torbie, był Grid Compass Computer 1109. Introduction to Coding , CADET used 324 point-contact transistors provided by the UK company Standard Telephones and Cables; 76 junction transistors were used for the first stage amplifiers for data read from the drum, since point-contact transistors were too noisy.