Inmos International plc and two operating subsidiaries, Inmos Limited and Inmos Corporation, was a British semiconductor company founded by Iann Barron, Richard Petritz, Paul Schroeder in July 1978. Inmos Limited's head office and design office were at Aztec West business park in England. Inmos' first products were static RAM devices, followed by dynamic EEPROMs. Despite early production difficulties, Inmos captured around 60% of the world SRAM market. However, Barron's long-term aim was to produce an innovative microprocessor architecture intended for parallel processing, the transputer. David May and Robert Milne were recruited to design this processor, which went into production in 1985 in the form of the T212 and T414 chips; the transputer achieved some success as the basis for several parallel supercomputers from companies such as Meiko, Floating Point Systems and Parsys. It was used in a few workstations, the most notable being the Atari Transputer Workstation. Being a self-contained design, it was used in some embedded systems.
However, the unconventional nature of the transputer and its native occam programming language limited its appeal. During the late 1980s, the transputer struggled to keep up with the ever-increasing performance of its competitors. Other devices produced by Inmos included the A100, A110 and A121 digital signal processors, G364 framebuffer, a line of video RAMDACs, including the G171, adopted by IBM for the original VGA graphics adapter used in the IBM PS/2; the company was founded by Iann Barron, a British computer consultant, Richard Petritz and Paul Schroeder, both American semiconductor industry veterans. Initial funding of £50m was provided by the UK government via the National Enterprise Board. A US subsidiary, Inmos Corporation, was established in Colorado. Semiconductor fabrication facilities were built in the US at Colorado Springs, Colorado and in the UK at Newport, South Wales. Under the privatization policy of Margaret Thatcher the National Enterprise Board was merged into the British Technology Group and had to sell its shares in Inmos.
Offers for Inmos from AT&T and a Dutch consortium had been turned down. In 1982, construction of the microprocessor factory in Newport, South Wales was completed. By July 1984 Thorn EMI had made a £124.1m bid for the state's 76% interest in the company. It was raised to £192 million, approved August 1984 and finalized in September. In total, Inmos did not become profitable. In April 1989, Inmos was sold to SGS-Thomson. Around the same time, work was started on an enhanced transputer, the T9000; this encountered various technical problems and delays, was abandoned, signalling the end of the development of the transputer as a parallel processing platform. However, transputer derivatives such as the ST20 were incorporated into chipsets for embedded applications such as set-top boxes. In December 1994, Inmos was assimilated into STMicroelectronics, the usage of the Inmos brand name was discontinued. Arthur Trew and Greg Wilson. Past, Parallel: A Survey of Available Parallel Computing Systems. New York: Springer-Verlag.
ISBN 0-387-19664-1 Mick McClean and Tom Rowland. The Inmos Saga. Quorum Books. ISBN 978-0-89930-165-5 Inmos and the transputer: part 1 and part 2 — a 1998 talk given by Iann Barron to the Computer Conservation Society of the British Computer Society Inmos ex-employee website Dick Selwood. "The Inmos legacy". Components in Electronics. Parsys SN9500 based on 32 x T9000 running at 20 MHz
Recursion (computer science)
Recursion in computer science is a method of solving a problem where the solution depends on solutions to smaller instances of the same problem. The approach can be applied to many types of problems, recursion is one of the central ideas of computer science; the power of recursion evidently lies in the possibility of defining an infinite set of objects by a finite statement. In the same manner, an infinite number of computations can be described by a finite recursive program if this program contains no explicit repetitions. Most computer programming languages support recursion by allowing a function to call itself from within its own code; some functional programming languages do not define any looping constructs but rely on recursion to call code. Computability theory proves. A common computer programming tactic is to divide a problem into sub-problems of the same type as the original, solve those sub-problems, combine the results; this is referred to as the divide-and-conquer method. A recursive function definition has one or more base cases, meaning input for which the function produces a result trivially, one or more recursive cases, meaning input for which the program recurs.
For example, the factorial function can be defined recursively by the equations 0! = 1 and, for all n > 0, n! = n!. Neither equation by itself constitutes a complete definition; because the base case breaks the chain of recursion, it is sometimes called the "terminating case". The job of the recursive cases can be seen as breaking down complex inputs into simpler ones. In a properly designed recursive function, with each recursive call, the input problem must be simplified in such a way that the base case must be reached. Neglecting to write a base case, or testing for it incorrectly, can cause an infinite loop. For some functions there is not an obvious base case implied by the input data; such an example is more treated by co-recursion, where successive terms in the output are the partial sums. Many computer programs must generate an arbitrarily large quantity of data. Recursion is one technique for representing data whose exact size the programmer does not know: the programmer can specify this data with a self-referential definition.
There are two types of self-referential definitions: coinductive definitions. An inductively defined recursive data definition is one that specifies how to construct instances of the data. For example, linked lists can be defined inductively: The code above specifies a list of strings to be either empty, or a structure that contains a string and a list of strings; the self-reference in the definition permits the construction of lists of any number of strings. Another example of inductive definition is the natural numbers: A natural number is either 1 or n+1, where n is a natural number. Recursive definitions are used to model the structure of expressions and statements in programming languages. Language designers express grammars in a syntax such as Backus–Naur form. By recursively referring to expressions in the second and third lines, the grammar permits arbitrarily complex arithmetic expressions such as, with more than one product or sum operation in a single expression. A coinductive data definition is one that specifies the operations that may be performed on a piece of data.
A coinductive definition of infinite streams of strings, given informally, might look like this: A stream of strings is an object s such that: head is a string, tail is a stream of strings. This is similar to an inductive definition of lists of strings. Corecursion is related to coinduction, can be used to compute particular instances of infinite objects; as a programming technique, it is used most in the context of lazy programming languages, can be preferable to recursion when the desired size or precision of a program's output is unknown. In such cases the program requires both a definition for an infinitely large result, a me
A microprocessor is a computer processor that incorporates the functions of a central processing unit on a single integrated circuit, or at most a few integrated circuits. The microprocessor is a multipurpose, clock driven, register based, digital integrated circuit that accepts binary data as input, processes it according to instructions stored in its memory, provides results as output. Microprocessors contain sequential digital logic. Microprocessors operate on symbols represented in the binary number system; the integration of a whole CPU onto a single or a few integrated circuits reduced the cost of processing power. Integrated circuit processors are produced in large numbers by automated processes, resulting in a low unit price. Single-chip processors increase reliability because there are many fewer electrical connections that could fail; as microprocessor designs improve, the cost of manufacturing a chip stays the same according to Rock's law. Before microprocessors, small computers had been built using racks of circuit boards with many medium- and small-scale integrated circuits.
Microprocessors combined this into a few large-scale ICs. Continued increases in microprocessor capacity have since rendered other forms of computers completely obsolete, with one or more microprocessors used in everything from the smallest embedded systems and handheld devices to the largest mainframes and supercomputers; the complexity of an integrated circuit is bounded by physical limitations on the number of transistors that can be put onto one chip, the number of package terminations that can connect the processor to other parts of the system, the number of interconnections it is possible to make on the chip, the heat that the chip can dissipate. Advancing technology makes more powerful chips feasible to manufacture. A minimal hypothetical microprocessor might include only an arithmetic logic unit, a control logic section; the ALU performs addition and operations such as AND or OR. Each operation of the ALU sets one or more flags in a status register, which indicate the results of the last operation.
The control logic retrieves instruction codes from memory and initiates the sequence of operations required for the ALU to carry out the instruction. A single operation code might affect many individual data paths and other elements of the processor; as integrated circuit technology advanced, it was feasible to manufacture more and more complex processors on a single chip. The size of data objects became larger. Additional features were added to the processor architecture. Floating-point arithmetic, for example, was not available on 8-bit microprocessors, but had to be carried out in software. Integration of the floating point unit first as a separate integrated circuit and as part of the same microprocessor chip sped up floating point calculations. Physical limitations of integrated circuits made such practices as a bit slice approach necessary. Instead of processing all of a long word on one integrated circuit, multiple circuits in parallel processed subsets of each data word. While this required extra logic to handle, for example and overflow within each slice, the result was a system that could handle, for example, 32-bit words using integrated circuits with a capacity for only four bits each.
The ability to put large numbers of transistors on one chip makes it feasible to integrate memory on the same die as the processor. This CPU cache has the advantage of faster access than off-chip memory and increases the processing speed of the system for many applications. Processor clock frequency has increased more than external memory speed, so cache memory is necessary if the processor is not delayed by slower external memory. A microprocessor is a general-purpose entity. Several specialized processing devices have followed: A digital signal processor is specialized for signal processing. Graphics processing units are processors designed for realtime rendering of images. Other specialized units exist for video machine vision. Microcontrollers integrate a microprocessor with peripheral devices in embedded systems. Systems on chip integrate one or more microprocessor or microcontroller cores. Microprocessors can be selected for differing applications based on their word size, a measure of their complexity.
Longer word sizes allow each clock cycle of a processor to carry out more computation, but correspond to physically larger integrated circuit dies with higher standby and operating power consumption. 4, 8 or 12 bit processors are integrated into microcontrollers operating embedded systems. Where a system is expected to handle larger volumes of data or require a more flexible user interface, 16, 32 or 64 bit processors are used. An 8- or 16-bit processor may be selected over a 32-bit processor for system on a chip or microcontroller applications that require low-power electronics, or are part of a mixed-signal integrated circuit with noise-sensitive on-chip analog electronics such as high-resolution analog to digital converters, or both. Running 32-bit arithmetic on an 8-bit chip could end up using more power, as the chip must execute software with multiple instructions. Thousands of items that were traditionally not computer-related inc
The transputer is a series of pioneering microprocessors from the 1980s, featuring integrated memory and serial communication links, intended for parallel computing. They were produced by Inmos, a semiconductor company based in Bristol, United Kingdom. For some time in the late 1980s, many considered the transputer to be the next great design for the future of computing. While Inmos and the transputer did not achieve this expectation, the transputer architecture was influential in provoking new ideas in computer architecture, several of which have re-emerged in different forms in modern systems. In the early 1980s, conventional central processing units appeared to reach a performance limit. Up to that time, manufacturing difficulties limited the amount of circuitry that could fit on a chip. Continued improvements in the fabrication process, removed this restriction. Within a decade, chips could hold more circuitry. Traditional complex instruction set computer designs were reaching a performance plateau, it wasn't clear it could be overcome.
It seemed that the only way forward was to increase the use of parallelism, as the use of several CPUs that would work together to solve several tasks at the same time. This depended on such machines being able to run several tasks at once, a process termed multiprocessing; this had been too difficult for prior CPU designs to handle, but more recent designs were able to accomplish it effectively. It was clear. A side effect of most multitasking design is that it also allows the processes to be run on physically different CPUs, in which case it is termed multiprocessing. A low-cost CPU built for multiprocessing could allow the speed of a machine to be raised by adding more CPUs far more cheaply than by using one faster CPU design; the first transputer designs were due to computer scientist David May and telecommunications consultant Robert Milne. In 1990, May received an Honorary DSc from University of Southampton, followed in 1991 by his election as a Fellow of The Royal Society and the award of the Patterson Medal of the Institute of Physics in 1992.
Tony Fuge a leading engineer at Inmos, was awarded the Prince Philip Designers Prize in 1987 for his work on the T414 transputer. The transputer was the first general purpose microprocessor designed to be used in parallel computing systems; the goal was to produce a family of chips ranging in power and cost that could be wired together to form a complete parallel computer. The name was selected to indicate the role the individual transputers would play: numbers of them would be used as basic building blocks, just as transistors had earlier; the plan was to make the transputer cost only a few dollars per unit. Inmos saw them being used for everything, from operating as the main CPU for a computer to acting as a channel controller for disk drives in the same machine. Spare cycles on any of these transputers could be used for other tasks increasing the overall performance of the machines. One transputer would have all the circuitry needed to work by itself, a feature more associated with microcontrollers.
The intent was to allow transputers to be connected together as as possible, with no need for a complex bus, or motherboard. Power and a simple clock signal had to be supplied, but little else: random-access memory, a RAM controller, bus support and a real-time operating system were all built in; the original transputer used a simple and rather unusual architecture to achieve a high performance in a small area. It used microcode as the main method to control the data path, but unlike other designs of the time, many instructions took only one cycle to execute. Instruction opcodes were used as the entry points to the microcode read-only memory and the outputs from the ROM were fed directly to the data path. For multi-cycle instructions, while the data path was performing the first cycle, the microcode decoded four possible options for the second cycle; the decision as to which of these options would be used could be made near the end of the first cycle. This allowed for fast operation while keeping the architecture generic.
The clock rate of 20 MHz was quite high for the era and the designers were concerned about the practicality of distributing such a fast clock signal on a board. A slower external clock of 5 MHz was used, this was multiplied up to the needed internal frequency using a phase-locked loop; the internal clock had four non-overlapping phases and designers were free to use whichever combination of these they wanted, so it could be argued that the transputer ran at 80 MHz. Dynamic logic was used in many parts of the design to reduce increase speed; these methods are difficult to combine with automatic test pattern generation scan testing so they fell out of favour for designs. Prentice-Hall published a book ISBN 978-0139290688 on the general principles of the Transputer; the basic design of the transputer included serial links that allowed it to communicate with up to four other transputers, each at 5, 10, or 20 Mbit/s –, fast for the 1980s. Any number of transputers could be connected together over links to form one computing farm.
A hypothetical desktop machine might have two of the "low end" transputers handling input/output tasks on some of their serial lines while they talked to one of their larger cousins acting as a CPU on another. This serial link is called an os-link. There were limits to the si
Inheritance (object-oriented programming)
In object-oriented programming, inheritance is the mechanism of basing an object or class upon another object or class, retaining similar implementation. Defined as deriving new classes from existing ones and forming them into a hierarchy of classes. In most class-based object-oriented languages, an object created through inheritance acquires all the properties and behaviors of the parent object. Inheritance allows programmers to create classes that are built upon existing classes, to specify a new implementation while maintaining the same behaviors, to reuse code and to independently extend original software via public classes and interfaces; the relationships of objects or classes through inheritance give rise to a directed graph. Inheritance was invented in 1969 for Simula. An inherited class is called a subclass of its parent class or super class; the term "inheritance" is loosely used for both class-based and prototype-based programming, but in narrow use the term is reserved for class-based programming, with the corresponding technique in prototype-based programming being instead called delegation.
Inheritance should not be confused with subtyping. In some languages inheritance and subtyping agree. To distinguish these concepts, subtyping is known as interface inheritance, whereas inheritance as defined here is known as implementation inheritance or code inheritance. Still, inheritance is a used mechanism for establishing subtype relationships. Inheritance is contrasted with object composition. Composition implements a has-a relationship, in contrast to the is-a relationship of subtyping. There are various types of inheritance, based on specific language. Single inheritance where subclasses inherit the features of one superclass. A class acquires the properties of another class. Multiple inheritance where one class can have more than one superclass and inherit features from all parent classes. "Multiple Inheritance was supposed to be difficult to implement efficiently. For example, in a summary of C++ in his book on objective C Brd. Cox claimed that adding Multiple inheritance to C++ was impossible.
Thus, multiple inheritance seemed more of a challenge. Since I had considered multiple inheritance as early as 1982 and found a simple and efficient implementation technique in 1984. I couldn't resist the challenge. I suspect this to be the only case in which fashion affected the sequence of events." In JDK 1.8, Java now has support for multiple inheritance. Multilevel inheritance, it is not uncommon that a class is derived from another derived class as shown in the figure "Multilevel inheritance". The class A serves as a base class for the derived class B, which in turn serves as a base class for the derived class C; the class B is known as intermediate base class because it provides a link for the inheritance between A and C. The chain ABC is known as inheritance path. A derived class with multilevel inheritance is declared as follows: This process can be extended to any number of levels. Hierarchical inheritance where one class serves as a superclass for more than one sub class. Hybrid inheritance a mix of two or more of the above types of inheritance.
Subclasses, derived classes, heir classes, or child classes are modular derivative classes that inherits one or more language entities from one or more other classes. The semantics of class inheritance vary from language to language, but the subclass automatically inherits the instance variables and member functions of its superclasses; the general form of defining a derived class is: The colon indicates that the subclass inherits from the superclass. The visibility, if present, may be either private or public; the default visibility is private. Visibility specifies whether the features of the base class are derived or publicly derived; some languages support the inheritance of other constructs. For example, in Eiffel, contracts that define the specification of a class are inherited by heirs; the superclass establishes a common interface and foundational functionality, which specialized subclasses can inherit and supplement. The software inherited by a subclass is considered reused in the subclass.
A reference to an instance of a class may be referring to one of its subclasses. The actual class of the object being referenced is impossible to predict at compile-time. A uniform interface is used to invoke the member functions of objects of a number of different classes. Subclasses may replace superclass functions with new functions that must share the same method signature. In some languages a class may be declared as non-subclassable by adding certain class modifiers to the class declaration. Examples include the final keyword in Java and C++11 onwards or the sealed keyword in C#; such modifiers are added to the class declaration before the class keyword and the class identifier declaration. Such non-subclassable classes restrict reusability when developers only
Sir Charles Antony Richard Hoare, is a British computer scientist. He developed the sorting algorithm quicksort in 1959/1960, he developed Hoare logic for verifying program correctness, the formal language communicating sequential processes to specify the interactions of concurrent processes and the inspiration for the occam programming language. Born in Colombo, Ceylon to British parents, Tony Hoare's father was a colonial civil servant and his mother was the daughter of a tea planter. Hoare was educated in England at the King's School in Canterbury, he studied Classics and Philosophy at Merton College, Oxford. On graduating in 1956 he did 18 months National Service in the Royal Navy, he returned to the University of Oxford in 1958 to study for a postgraduate certificate in Statistics, it was here that he began computer programming, having been taught Autocode on the Ferranti Mercury by Leslie Fox. He went to Moscow State University as a British Council exchange student, where he studied machine translation under Andrey Kolmogorov.
In 1960, Hoare left the Soviet Union and began working at Elliott Brothers Ltd, a small computer manufacturing firm located in London, where he implemented ALGOL 60 and began developing major algorithms. He became the Professor of Computing Science at the Queen's University of Belfast in 1968, in 1977 returned to Oxford as the Professor of Computing to lead the Programming Research Group in the Oxford University Computing Laboratory, following the death of Christopher Strachey, he is now an Emeritus Professor there, is a principal researcher at Microsoft Research in Cambridge, England. Hoare's most significant work has been in the following areas: his sorting and selection algorithm, Hoare logic, the formal language Communicating Sequential Processes used to specify the interactions between concurrent processes, structuring computer operating systems using the monitor concept, the axiomatic specification of programming languages. Speaking at a software conference called QCon London in 2009, he apologised for inventing the null reference: I call it my billion-dollar mistake.
It was the invention of the null reference in 1965. At that time, I was designing the first comprehensive type system for references in an object oriented language. My goal was to ensure that all use of references should be safe, with checking performed automatically by the compiler, but I couldn't resist the temptation to put in a null reference because it was so easy to implement. This has led to innumerable errors and system crashes, which have caused a billion dollars of pain and damage in the last forty years. For many years under his leadership his Oxford department worked on formal specification languages such as CSP and Z; these did not achieve the expected take-up by industry, in 1995 Hoare was led to reflect upon the original assumptions: Ten years ago, researchers into formal methods predicted that the programming world would embrace with gratitude every assistance promised by formalisation to solve the problems of reliability that arise when programs get large and more safety-critical.
Programs have now got large and critical – well beyond the scale which can be comfortably tackled by formal methods. There have been many problems and failures, but these have nearly always been attributable to inadequate analysis of requirements or inadequate management control, it has turned out that the world just does not suffer from the kind of problem that our research was intended to solve. O.-J. Dahl, E. W. Dijkstra and C. A. R. Hoare. Structured Programming. Academic Press. ISBN 978-0-12-200550-3. OCLC 23937947. C. A. R. Hoare. Communicating Sequential Processes. Prentice Hall International Series in Computer Science. ISBN 978-0131532717 or ISBN 978-0131532892. C. A. R. Hoare and M. J. C. Gordon. Mechanised Reasoning and Hardware Design. Prentice Hall International Series in Computer Science. ISBN 978-0-13-572405-7. OCLC 25712842. C. A. R. Hoare and He Jifeng. Unifying Theories of Programming. Prentice Hall International Series in Computer Science. ISBN 978-0-13-458761-5. OCLC 38199961. In 1962, Hoare married a member of his research team.
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Occam's razor is the problem-solving principle that states that "simpler solutions are more to be correct than complex ones." When presented with competing hypotheses to solve a problem, one should select the solution with the fewest assumptions. The idea is attributed to English Franciscan friar William of Ockham, a scholastic philosopher and theologian. In science, Occam's razor is used as an abductive heuristic in the development of theoretical models, rather than as a rigorous arbiter between candidate models. In the scientific method, Occam's razor is not considered an irrefutable principle of logic or a scientific result. For each accepted explanation of a phenomenon, there may be an large even incomprehensible, number of possible and more complex alternatives. Since one can always burden failing explanations with ad hoc hypotheses to prevent them from being falsified, simpler theories are preferable to more complex ones because they are more testable; the term Occam's razor did not appear until a few centuries after William of Ockham's death in 1347.
Libert Froidmont, in his On Christian Philosophy of the Soul, takes credit for the phrase, speaking of "novacula occami". Ockham did not invent this principle, but the "razor"—and its association with him—may be due to the frequency and effectiveness with which he used it. Ockham stated the principle in various ways, but the most popular version, "Entities are not to be multiplied without necessity" was formulated by the Irish Franciscan philosopher John Punch in his 1639 commentary on the works of Duns Scotus; the origins of what has come to be known as Occam's razor are traceable to the works of earlier philosophers such as John Duns Scotus, Robert Grosseteste and Aristotle. Aristotle writes in his Posterior Analytics, "We may assume the superiority ceteris paribus of the demonstration which derives from fewer postulates or hypotheses." Ptolemy stated, "We consider it a good principle to explain the phenomena by the simplest hypothesis possible."Phrases such as "It is vain to do with more what can be done with fewer" and "A plurality is not to be posited without necessity" were commonplace in 13th-century scholastic writing.
Robert Grosseteste, in Commentary on the Posterior Analytics Books, declares: "That is better and more valuable which requires fewer, other circumstances being equal... For if one thing were demonstrated from many and another thing from fewer known premises, better, from fewer because it makes us know just as a universal demonstration is better than particular because it produces knowledge from fewer premises. In natural science, in moral science, in metaphysics the best is that which needs no premises and the better that which needs the fewer, other circumstances being equal."The Summa Theologica of Thomas Aquinas states that "it is superfluous to suppose that what can be accounted for by a few principles has been produced by many." Aquinas uses this principle to construct an objection to God's existence, an objection that he in turn answers and refutes and through an argument based on causality. Hence, Aquinas acknowledges the principle that today is known as Occam's razor, but prefers causal explanations to other simple explanations.
William of Ockham was an English Franciscan friar and theologian, an influential medieval philosopher and a nominalist. His popular fame as a great logician rests chiefly on the maxim attributed to him and known as Occam's razor; the term razor refers to distinguishing between two hypotheses either by "shaving away" unnecessary assumptions or cutting apart two similar conclusions. While it has been claimed that Occam's razor is not found in any of William's writings, one can cite statements such as Numquam ponenda est pluralitas sine necessitate, which occurs in his theological work on the Sentences of Peter Lombard; the precise words sometimes attributed to William of Ockham, Entia non sunt multiplicanda praeter necessitatem, are absent in his extant works. William of Ockham's contribution seems to restrict the operation of this principle in matters pertaining to miracles and God's power; this principle is sometimes phrased as Pluralitas non est ponenda sine necessitate. In his Summa Totius Logicae, i.
12, William of Ockham cites the principle of economy, Frustra fit per plura quod potest fieri per pauciora To quote Isaac Newton, "We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances. Therefore, to the same natural effects we must, as far as possible, assign the same cause