1.
Decimal
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This article aims to be an accessible introduction. For the mathematical definition, see Decimal representation, the decimal numeral system has ten as its base, which, in decimal, is written 10, as is the base in every positional numeral system. It is the base most widely used by modern civilizations. Decimal fractions have terminating decimal representations and other fractions have repeating decimal representations, Decimal notation is the writing of numbers in a base-ten numeral system. Examples are Brahmi numerals, Greek numerals, Hebrew numerals, Roman numerals, Roman numerals have symbols for the decimal powers and secondary symbols for half these values. Brahmi numerals have symbols for the nine numbers 1–9, the nine decades 10–90, plus a symbol for 100, Chinese numerals have symbols for 1–9, and additional symbols for powers of ten, which in modern usage reach 1072. Positional decimal systems include a zero and use symbols for the ten values to represent any number, positional notation uses positions for each power of ten, units, tens, hundreds, thousands, etc. The position of each digit within a number denotes the multiplier multiplied with that position has a value ten times that of the position to its right. There were at least two independent sources of positional decimal systems in ancient civilization, the Chinese counting rod system. Ten is the number which is the count of fingers and thumbs on both hands, the English word digit as well as its translation in many languages is also the anatomical term for fingers and toes. In English, decimal means tenth, decimate means reduce by a tenth, however, the symbols used in different areas are not identical, for instance, Western Arabic numerals differ from the forms used by other Arab cultures. A decimal fraction is a fraction the denominator of which is a power of ten. g, Decimal fractions 8/10, 1489/100, 24/100000, and 58900/10000 are expressed in decimal notation as 0.8,14.89,0.00024,5.8900 respectively. In English-speaking, some Latin American and many Asian countries, a period or raised period is used as the separator, in many other countries, particularly in Europe. The integer part, or integral part of a number is the part to the left of the decimal separator. The part from the separator to the right is the fractional part. It is usual for a number that consists only of a fractional part to have a leading zero in its notation. Any rational number with a denominator whose only prime factors are 2 and/or 5 may be expressed as a decimal fraction and has a finite decimal expansion. 1/2 =0.5 1/20 =0.05 1/5 =0.2 1/50 =0.02 1/4 =0.25 1/40 =0.025 1/25 =0.04 1/8 =0.125 1/125 =0.008 1/10 =0
2.
Metric prefix
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A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or fraction of the unit. While all metric prefixes in use today are decadic, historically there have been a number of binary metric prefixes as well. Each prefix has a symbol that is prepended to the unit symbol. The prefix kilo-, for example, may be added to gram to indicate multiplication by one thousand, the prefix milli-, likewise, may be added to metre to indicate division by one thousand, one millimetre is equal to one thousandth of a metre. Decimal multiplicative prefixes have been a feature of all forms of the system with six dating back to the systems introduction in the 1790s. Metric prefixes have even been prepended to non-metric units, the SI prefixes are standardized for use in the International System of Units by the International Bureau of Weights and Measures in resolutions dating from 1960 to 1991. Since 2009, they have formed part of the International System of Quantities, the BIPM specifies twenty prefixes for the International System of Units. Each prefix name has a symbol which is used in combination with the symbols for units of measure. For example, the symbol for kilo- is k, and is used to produce km, kg, and kW, which are the SI symbols for kilometre, kilogram, prefixes corresponding to an integer power of one thousand are generally preferred. Hence 100 m is preferred over 1 hm or 10 dam, the prefixes hecto, deca, deci, and centi are commonly used for everyday purposes, and the centimetre is especially common. However, some building codes require that the millimetre be used in preference to the centimetre, because use of centimetres leads to extensive usage of decimal points. Prefixes may not be used in combination and this also applies to mass, for which the SI base unit already contains a prefix. For example, milligram is used instead of microkilogram, in the arithmetic of measurements having units, the units are treated as multiplicative factors to values. If they have prefixes, all but one of the prefixes must be expanded to their numeric multiplier,1 km2 means one square kilometre, or the area of a square of 1000 m by 1000 m and not 1000 square metres. 2 Mm3 means two cubic megametres, or the volume of two cubes of 1000000 m by 1000000 m by 1000000 m or 2×1018 m3, and not 2000000 cubic metres, examples 5 cm = 5×10−2 m =5 ×0.01 m =0. The prefixes, including those introduced after 1960, are used with any metric unit, metric prefixes may also be used with non-metric units. The choice of prefixes with a unit is usually dictated by convenience of use. Unit prefixes for amounts that are larger or smaller than those actually encountered are seldom used
3.
Gigabyte
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The gigabyte is a multiple of the unit byte for digital information. The prefix giga means 109 in the International System of Units, the unit symbol for the gigabyte is GB. However, the term is used in some fields of computer science and information technology to denote 1073741824 bytes. The use of gigabyte may thus be ambiguous, to address this ambiguity, the International System of Quantities standardizes the binary prefixes which denote a series of integer powers of 1024. With these prefixes, a module that is labeled as having the size 1GB has one gibibyte of storage capacity. The term gigabyte is commonly used to mean either 10003 bytes or 10243 bytes, the latter binary usage originated as compromise technical jargon for byte multiples that needed to be expressed in a power of 2, but lacked a convenient name. As 1024 is approximately 1000, roughly corresponding to SI multiples, in 1998 the International Electrotechnical Commission published standards for binary prefixes, requiring that the gigabyte strictly denote 10003 bytes and gibibyte denote 10243 bytes. By the end of 2007, the IEC Standard had been adopted by the IEEE, EU, and NIST and this is the recommended definition by the International Electrotechnical Commission. The file manager of Mac OS X version 10.6 and later versions are an example of this usage in software. The binary definition uses powers of the base 2, as is the principle of binary computers. This usage is widely promulgated by some operating systems, such as Microsoft Windows in reference to computer memory and this definition is synonymous with the unambiguous unit gibibyte. Since the first disk drive, the IBM350, disk drive manufacturers expressed hard drive capacities using decimal prefixes, with the advent of gigabyte-range drive capacities, manufacturers based most consumer hard drive capacities in certain size classes expressed in decimal gigabytes, such as 500 GB. The exact capacity of a given model is usually slightly larger than the class designation. Practically all manufacturers of disk drives and flash-memory disk devices continue to define one gigabyte as 1000000000bytes. Some operating systems such as OS X express hard drive capacity or file size using decimal multipliers and this discrepancy causes confusion, as a disk with an advertised capacity of, for example,400 GB might be reported by the operating system as 372 GB, meaning 372 GiB. The JEDEC memory standards use IEEE100 nomenclature which quote the gigabyte as 1073741824bytes and this means that a 300 GB hard disk might be indicated variously as 300 GB,279 GB or 279 GiB, depending on the operating system. As storage sizes increase and larger units are used, these differences even more pronounced. Some legal challenges have been waged over this confusion such as a lawsuit against drive manufacturer Western Digital, Western Digital settled the challenge and added explicit disclaimers to products that the usable capacity may differ from the advertised capacity
4.
Binary prefix
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A binary prefix is a unit prefix for multiples of units in data processing, data transmission, and digital information, notably the bit and the byte, to indicate multiplication by a power of 2. The computer industry has used the units kilobyte, megabyte, and gigabyte, and the corresponding symbols KB, MB. In citations of main memory capacity, gigabyte customarily means 1073741824 bytes, as this is the third power of 1024, and 1024 is a power of two, this usage is referred to as a binary measurement. In most other contexts, the uses the multipliers kilo, mega, giga, etc. in a manner consistent with their meaning in the International System of Units. For example, a 500 gigabyte hard disk holds 500000000000 bytes, in contrast with the binary prefix usage, this use is described as a decimal prefix, as 1000 is a power of 10. The use of the same unit prefixes with two different meanings has caused confusion, in 2008, the IEC prefixes were incorporated into the ISO/IEC80000 standard. Early computers used one of two addressing methods to access the memory, binary or decimal. For example, the IBM701 used binary and could address 2048 words of 36 bits each, while the IBM702 used decimal, by the mid-1960s, binary addressing had become the standard architecture in most computer designs, and main memory sizes were most commonly powers of two. Early computer system documentation would specify the size with an exact number such as 4096,8192. These are all powers of two, and furthermore are small multiples of 210, or 1024, as storage capacities increased, several different methods were developed to abbreviate these quantities. The method most commonly used today uses prefixes such as kilo, mega, giga, and corresponding symbols K, M, and G, the prefixes kilo- and mega-, meaning 1000 and 1000000 respectively, were commonly used in the electronics industry before World War II. Along with giga- or G-, meaning 1000000000, they are now known as SI prefixes after the International System of Units, introduced in 1960 to formalize aspects of the metric system. The International System of Units does not define units for digital information and this usage is not consistent with the SI. Compliance with the SI requires that the prefixes take their 1000-based meaning, the use of K in the binary sense as in a 32K core meaning 32 ×1024 words, i. e.32768 words, can be found as early as 1959. Gene Amdahls seminal 1964 article on IBM System/360 used 1K to mean 1024 and this style was used by other computer vendors, the CDC7600 System Description made extensive use of K as 1024. Thus the first binary prefix was born, the exact values 32768 words,65536 words and 131072 words would then be described as 32K, 65K and 131K. This style was used from about 1965 to 1975 and these two styles were used loosely around the same time, sometimes by the same company. In discussions of binary-addressed memories, the size was evident from context
5.
Byte
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The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of used to encode a single character of text in a computer. The size of the byte has historically been hardware dependent and no standards existed that mandated the size. The de-facto standard of eight bits is a convenient power of two permitting the values 0 through 255 for one byte, the international standard IEC 80000-13 codified this common meaning. Many types of applications use information representable in eight or fewer bits, the popularity of major commercial computing architectures has aided in the ubiquitous acceptance of the 8-bit size. The unit symbol for the byte was designated as the upper-case letter B by the IEC and IEEE in contrast to the bit, internationally, the unit octet, symbol o, explicitly denotes a sequence of eight bits, eliminating the ambiguity of the byte. It is a respelling of bite to avoid accidental mutation to bit. Early computers used a variety of four-bit binary coded decimal representations and these representations included alphanumeric characters and special graphical symbols. S. Government and universities during the 1960s, the prominence of the System/360 led to the ubiquitous adoption of the eight-bit storage size, while in detail the EBCDIC and ASCII encoding schemes are different. In the early 1960s, AT&T introduced digital telephony first on long-distance trunk lines and these used the eight-bit µ-law encoding. This large investment promised to reduce costs for eight-bit data. The development of microprocessors in the 1970s popularized this storage size. A four-bit quantity is called a nibble, also nybble. The term octet is used to specify a size of eight bits. It is used extensively in protocol definitions, historically, the term octad or octade was used to denote eight bits as well at least in Western Europe, however, this usage is no longer common. The exact origin of the term is unclear, but it can be found in British, Dutch, and German sources of the 1960s and 1970s, and throughout the documentation of Philips mainframe computers. The unit symbol for the byte is specified in IEC 80000-13, IEEE1541, in the International System of Quantities, B is the symbol of the bel, a unit of logarithmic power ratios named after Alexander Graham Bell, creating a conflict with the IEC specification. However, little danger of confusion exists, because the bel is a used unit
6.
International System of Units
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The International System of Units is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units, the system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system was published in 1960 as the result of an initiative began in 1948. It is based on the system of units rather than any variant of the centimetre-gram-second system. The motivation for the development of the SI was the diversity of units that had sprung up within the CGS systems, the International System of Units has been adopted by most developed countries, however, the adoption has not been universal in all English-speaking countries. The metric system was first implemented during the French Revolution with just the metre and kilogram as standards of length, in the 1830s Carl Friedrich Gauss laid the foundations for a coherent system based on length, mass, and time. In the 1860s a group working under the auspices of the British Association for the Advancement of Science formulated the requirement for a coherent system of units with base units and derived units. Meanwhile, in 1875, the Treaty of the Metre passed responsibility for verification of the kilogram, in 1921, the Treaty was extended to include all physical quantities including electrical units originally defined in 1893. The units associated with these quantities were the metre, kilogram, second, ampere, kelvin, in 1971, a seventh base quantity, amount of substance represented by the mole, was added to the definition of SI. On 11 July 1792, the proposed the names metre, are, litre and grave for the units of length, area, capacity. The committee also proposed that multiples and submultiples of these units were to be denoted by decimal-based prefixes such as centi for a hundredth, on 10 December 1799, the law by which the metric system was to be definitively adopted in France was passed. Prior to this, the strength of the magnetic field had only been described in relative terms. The technique used by Gauss was to equate the torque induced on a magnet of known mass by the earth’s magnetic field with the torque induced on an equivalent system under gravity. The resultant calculations enabled him to assign dimensions based on mass, length, a French-inspired initiative for international cooperation in metrology led to the signing in 1875 of the Metre Convention. Initially the convention only covered standards for the metre and the kilogram, one of each was selected at random to become the International prototype metre and International prototype kilogram that replaced the mètre des Archives and kilogramme des Archives respectively. Each member state was entitled to one of each of the prototypes to serve as the national prototype for that country. Initially its prime purpose was a periodic recalibration of national prototype metres. The official language of the Metre Convention is French and the version of all official documents published by or on behalf of the CGPM is the French-language version
7.
International System of Quantities
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The International System of Quantities is a system based on seven base quantities, length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity. Other quantities such as area, pressure, and electrical resistance are derived from these base quantities by clear, the ISQ defines the quantities that are measured with the SI units and also includes many other quantities in modern science and technology. The ISQ is defined in the international standard ISO/IEC80000, and was finalised in 2009 with the publication of ISO 80000-1. The 14 parts of ISO/IEC80000 define quantities used in disciplines such as mechanics, light, acoustics, electromagnetism, information technology, chemistry, mathematics. A base quantity is a quantity in a subset of a given system of quantities that is chosen by convention. The ISQ defines seven base quantities, the symbols for them, as for other quantities, are written in italics. The dimension of a quantity does not include magnitude or units. The conventional symbolic representation of the dimension of a quantity is a single upper-case letter in roman sans-serif type. A derived quantity is a quantity in a system of quantities that is a defined in terms of the quantities of that system. The ISQ defines many derived quantities, the conventional symbolic representation of the dimension of a derived quantity is the product of powers of the dimensions of the base quantities according to the definition of the derived quantity. The dimension of a quantity is denoted by L a M b T c I d Θ e N f J g, the symbol may be omitted if its exponent is zero. For example, in the ISQ, the quantity dimension of velocity is denoted L T −1, the following table lists some quantities defined by the ISQ. A quantity of one is historically known as a dimensionless quantity, all its dimensional exponents are zero. Such a quantity can be regarded as a quantity in the form of the ratio of two quantities of the same dimension. In the ISQ, the level of a quantity Q is defined as logr, an example of level is sound pressure level. All levels of the ISQ are derived quantities, B. N. Taylor, Ambler Thompson, International System of Units, National Institute of Standards and Technology 2008 edition, ISBN 1-4379-1558-2
8.
International Electrotechnical Commission
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The IEC also manages three global conformity assessment systems that certify whether equipment, system or components conform to its International Standards. The first International Electrical Congress took place in 1881 at the International Exposition of Electricity, at that time the International System of Electrical and Magnetic Units was agreed to. The IEC was instrumental in developing and distributing standards for units of measurement, particularly Gauss, Hertz and it also first proposed a system of standards, the Giorgi System, which ultimately became the SI, or Système International d’unités. In 1938, it published a multilingual international vocabulary to unify terminology relating to electrical, electronic and this effort continues, and the International Electrotechnical Vocabulary remains an important work in the electrical and electronic industries. The CISPR – in English, the International Special Committee on Radio Interference – is one of the groups founded by the IEC, originally located in London, the commission moved to its current headquarters in Geneva in 1948. It has regional centres in Asia-Pacific, Latin America and North America, today, the IEC is the worlds leading international organization in its field, and its standards are adopted as national standards by its members. The work is done by some 10,000 electrical and electronics experts from industry, government, academia, test labs, IEC standards have numbers in the range 60000–79999 and their titles take a form such as IEC60417, Graphical symbols for use on equipment. Following the Dresden Agreement with CENELEC the numbers of older IEC standards were converted in 1997 by adding 60000, for example IEC27 became IEC60027. Standards of the 60000 series are also preceded by EN to indicate that the IEC standard is also adopted by CENELEC as a European standard. The IEC cooperates closely with the International Organization for Standardization and the International Telecommunication Union, Standards developed jointly with ISO such as ISO/IEC26300, ISO/IEC27001, and CASCO ISO/IEC17000 series, carry the acronym of both organizations. The use of the ISO/IEC prefix covers publications from ISO/IEC Joint Technical Committee 1 - Information Technology, as well as conformity assessment standards developed by ISO CASCO, other standards developed in cooperation between IEC and ISO are assigned numbers in the 80000 series, such as IEC 82045-1. IEC standards are also being adopted by other certifying bodies such as BSI, CSA, UL & ANSI/INCITS, SABS, SAI, SPC/GB, IEC standards adopted by other certifying bodies may have some noted differences from the original IEC standard. The IEC is made up of members, called national committees, national committees are constituted in different ways. Some NCs are public sector only, some are a combination of public and private sector, about 90% of those who prepare IEC standards work in industry
9.
Institute of Electrical and Electronics Engineers
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The Institute of Electrical and Electronics Engineers is a professional association with its corporate office in New York City and its operations center in Piscataway, New Jersey. It was formed in 1963 from the amalgamation of the American Institute of Electrical Engineers, today, it is the worlds largest association of technical professionals with more than 400,000 members in chapters around the world. Its objectives are the educational and technical advancement of electrical and electronic engineering, telecommunications, computer engineering, IEEE stands for the Institute of Electrical and Electronics Engineers. The association is chartered under this full legal name, IEEEs membership has long been composed of engineers and scientists. For this reason the organization no longer goes by the name, except on legal business documents. The IEEE is dedicated to advancing technological innovation and excellence and it has about 430,000 members in about 160 countries, slightly less than half of whom reside in the United States. The major interests of the AIEE were wire communications and light, the IRE concerned mostly radio engineering, and was formed from two smaller organizations, the Society of Wireless and Telegraph Engineers and the Wireless Institute. After World War II, the two became increasingly competitive, and in 1961, the leadership of both the IRE and the AIEE resolved to consolidate the two organizations. The two organizations merged as the IEEE on January 1,1963. The IEEE is incorporated under the Not-for-Profit Corporation Law of the state of New York and it was formed in 1963 by the merger of the Institute of Radio Engineers and the American Institute of Electrical Engineers. The IEEE serves as a publisher of scientific journals and organizer of conferences, workshops. IEEE develops and participates in activities such as accreditation of electrical engineering programs in institutes of higher learning. The IEEE logo is a design which illustrates the right hand grip rule embedded in Benjamin Franklins kite. IEEE has a dual complementary regional and technical structure – with organizational units based on geography and it manages a separate organizational unit which recommends policies and implements programs specifically intended to benefit the members, the profession and the public in the United States. The IEEE includes 39 technical Societies, organized around specialized technical fields, the IEEE Standards Association is in charge of the standardization activities of the IEEE. The IEEE History Center became an organization to the Engineering. The new ETHW is an effort by various engineering societies as a formal repository of topic articles, oral histories, first-hand histories, Landmarks + Milestones. The IEEE History Center is annexed to Stevens University Hoboken, NJ, in 2016, the IEEE acquired GlobalSpec, adding the provision of engineering data for a profit to its organizational portfolio
10.
European Union
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The European Union is a political and economic union of 28 member states that are located primarily in Europe. It has an area of 4,475,757 km2, the EU has developed an internal single market through a standardised system of laws that apply in all member states. Within the Schengen Area, passport controls have been abolished, a monetary union was established in 1999 and came into full force in 2002, and is composed of 19 EU member states which use the euro currency. The EU operates through a system of supranational and intergovernmental decision-making. The EU traces its origins from the European Coal and Steel Community, the community and its successors have grown in size by the accession of new member states and in power by the addition of policy areas to its remit. While no member state has left the EU or its antecedent organisations, the Maastricht Treaty established the European Union in 1993 and introduced European citizenship. The latest major amendment to the basis of the EU. The EU as a whole is the largest economy in the world, additionally,27 out of 28 EU countries have a very high Human Development Index, according to the United Nations Development Programme. In 2012, the EU was awarded the Nobel Peace Prize, through the Common Foreign and Security Policy, the EU has developed a role in external relations and defence. The union maintains permanent diplomatic missions throughout the world and represents itself at the United Nations, the World Trade Organization, the G7, because of its global influence, the European Union has been described as an emerging superpower. After World War II, European integration was seen as an antidote to the nationalism which had devastated the continent. 1952 saw the creation of the European Coal and Steel Community, the supporters of the Community included Alcide De Gasperi, Jean Monnet, Robert Schuman, and Paul-Henri Spaak. These men and others are credited as the Founding fathers of the European Union. In 1957, Belgium, France, Italy, Luxembourg, the Netherlands and West Germany signed the Treaty of Rome and they also signed another pact creating the European Atomic Energy Community for co-operation in developing nuclear energy. Both treaties came into force in 1958, the EEC and Euratom were created separately from the ECSC, although they shared the same courts and the Common Assembly. The EEC was headed by Walter Hallstein and Euratom was headed by Louis Armand, Euratom was to integrate sectors in nuclear energy while the EEC would develop a customs union among members. During the 1960s, tensions began to show, with France seeking to limit supranational power, Jean Rey presided over the first merged Commission. In 1973, the Communities enlarged to include Denmark, Ireland, Norway had negotiated to join at the same time, but Norwegian voters rejected membership in a referendum
11.
International Organization for Standardization
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The International Organization for Standardization is an international standard-setting body composed of representatives from various national standards organizations. Founded on 23 February 1947, the organization promotes worldwide proprietary and it is headquartered in Geneva, Switzerland, and as of March 2017 works in 162 countries. It was one of the first organizations granted general consultative status with the United Nations Economic, ISO, the International Organization for Standardization, is an independent, non-governmental organization, the members of which are the standards organizations of the 162 member countries. It is the worlds largest developer of international standards and facilitates world trade by providing common standards between nations. Nearly twenty thousand standards have been set covering everything from manufactured products and technology to food safety, use of the standards aids in the creation of products and services that are safe, reliable and of good quality. The standards help businesses increase productivity while minimizing errors and waste, by enabling products from different markets to be directly compared, they facilitate companies in entering new markets and assist in the development of global trade on a fair basis. The standards also serve to safeguard consumers and the end-users of products and services, the three official languages of the ISO are English, French, and Russian. The name of the organization in French is Organisation internationale de normalisation, according to the ISO, as its name in different languages would have different abbreviations, the organization adopted ISO as its abbreviated name in reference to the Greek word isos. However, during the meetings of the new organization, this Greek word was not invoked. Both the name ISO and the logo are registered trademarks, the organization today known as ISO began in 1926 as the International Federation of the National Standardizing Associations. ISO is an organization whose members are recognized authorities on standards. Members meet annually at a General Assembly to discuss ISOs strategic objectives, the organization is coordinated by a Central Secretariat based in Geneva. A Council with a membership of 20 member bodies provides guidance and governance. The Technical Management Board is responsible for over 250 technical committees, ISO has formed joint committees with the International Electrotechnical Commission to develop standards and terminology in the areas of electrical and electronic related technologies. Information technology ISO/IEC Joint Technical Committee 1 was created in 1987 to evelop, maintain, ISO has three membership categories, Member bodies are national bodies considered the most representative standards body in each country. These are the members of ISO that have voting rights. Correspondent members are countries that do not have their own standards organization and these members are informed about ISOs work, but do not participate in standards promulgation. Subscriber members are countries with small economies and they pay reduced membership fees, but can follow the development of standards
12.
NIST
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The National Institute of Standards and Technology is a measurement standards laboratory, and a non-regulatory agency of the United States Department of Commerce. Its mission is to promote innovation and industrial competitiveness, in 1821, John Quincy Adams had declared Weights and measures may be ranked among the necessities of life to every individual of human society. From 1830 until 1901, the role of overseeing weights and measures was carried out by the Office of Standard Weights and Measures, president Theodore Roosevelt appointed Samuel W. Stratton as the first director. The budget for the first year of operation was $40,000, a laboratory site was constructed in Washington, DC, and instruments were acquired from the national physical laboratories of Europe. In addition to weights and measures, the Bureau developed instruments for electrical units, in 1905 a meeting was called that would be the first National Conference on Weights and Measures. Quality standards were developed for products including some types of clothing, automobile brake systems and headlamps, antifreeze, during World War I, the Bureau worked on multiple problems related to war production, even operating its own facility to produce optical glass when European supplies were cut off. Between the wars, Harry Diamond of the Bureau developed a blind approach radio aircraft landing system, in 1948, financed by the Air Force, the Bureau began design and construction of SEAC, the Standards Eastern Automatic Computer. The computer went into operation in May 1950 using a combination of vacuum tubes, about the same time the Standards Western Automatic Computer, was built at the Los Angeles office of the NBS and used for research there. A mobile version, DYSEAC, was built for the Signal Corps in 1954, due to a changing mission, the National Bureau of Standards became the National Institute of Standards and Technology in 1988. Following 9/11, NIST conducted the investigation into the collapse of the World Trade Center buildings. NIST had a budget for fiscal year 2007 of about $843.3 million. NISTs 2009 budget was $992 million, and it also received $610 million as part of the American Recovery, NIST employs about 2,900 scientists, engineers, technicians, and support and administrative personnel. About 1,800 NIST associates complement the staff, in addition, NIST partners with 1,400 manufacturing specialists and staff at nearly 350 affiliated centers around the country. NIST publishes the Handbook 44 that provides the Specifications, tolerances, the Congress of 1866 made use of the metric system in commerce a legally protected activity through the passage of Metric Act of 1866. NIST is headquartered in Gaithersburg, Maryland, and operates a facility in Boulder, nISTs activities are organized into laboratory programs and extramural programs. Effective October 1,2010, NIST was realigned by reducing the number of NIST laboratory units from ten to six, nISTs Boulder laboratories are best known for NIST‑F1, which houses an atomic clock. NIST‑F1 serves as the source of the official time. NIST also operates a neutron science user facility, the NIST Center for Neutron Research, the NCNR provides scientists access to a variety of neutron scattering instruments, which they use in many research fields
13.
Computer network
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A computer network or data network is a telecommunications network which allows nodes to share resources. In computer networks, networked computing devices exchange data with other using a data link. The connections between nodes are established using either cable media or wireless media, the best-known computer network is the Internet. Network computer devices that originate, route and terminate the data are called network nodes, nodes can include hosts such as personal computers, phones, servers as well as networking hardware. Two such devices can be said to be networked together when one device is able to exchange information with the other device, Computer networks differ in the transmission medium used to carry their signals, communications protocols to organize network traffic, the networks size, topology and organizational intent. In most cases, application-specific communications protocols are layered over other more general communications protocols and this formidable collection of information technology requires skilled network management to keep it all running reliably. The chronology of significant computer-network developments includes, In the late 1950s, in 1960, the commercial airline reservation system semi-automatic business research environment went online with two connected mainframes. Licklider developed a group he called the Intergalactic Computer Network. In 1964, researchers at Dartmouth College developed the Dartmouth Time Sharing System for distributed users of computer systems. The same year, at Massachusetts Institute of Technology, a group supported by General Electric and Bell Labs used a computer to route. Throughout the 1960s, Leonard Kleinrock, Paul Baran, and Donald Davies independently developed network systems that used packets to transfer information between computers over a network, in 1965, Thomas Marill and Lawrence G. Roberts created the first wide area network. This was an precursor to the ARPANET, of which Roberts became program manager. Also in 1965, Western Electric introduced the first widely used telephone switch that implemented true computer control, in 1972, commercial services using X.25 were deployed, and later used as an underlying infrastructure for expanding TCP/IP networks. In July 1976, Robert Metcalfe and David Boggs published their paper Ethernet, Distributed Packet Switching for Local Computer Networks, in 1979, Robert Metcalfe pursued making Ethernet an open standard. In 1976, John Murphy of Datapoint Corporation created ARCNET, a network first used to share storage devices. In 1995, the transmission speed capacity for Ethernet increased from 10 Mbit/s to 100 Mbit/s, by 1998, Ethernet supported transmission speeds of a Gigabit. Subsequently, higher speeds of up to 100 Gbit/s were added, the ability of Ethernet to scale easily is a contributing factor to its continued use. Providing access to information on shared storage devices is an important feature of many networks, a network allows sharing of files, data, and other types of information giving authorized users the ability to access information stored on other computers on the network
14.
Data storage
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A data storage device is a device for recording information. A storage device may hold information, process information, or both, a device that only holds information is a recording medium. Devices that process information may either access a separate portable recording medium or a permanent component to store, Electronic data storage requires electrical power to store and retrieve that data. Most storage devices that do not require vision and a brain to read data fall into this category, electromagnetic data may be stored in either an analog data or digital data format on a variety of media. Most electronically processed data storage media are considered permanent storage, that is, in contrast, most electronically stored information within most types of semiconductor microcircuits are volatile memory, for it vanishes if power is removed. JISC/NPO Studies on the Preservation of Electronic Materials, A Framework of Data Types and Formats, british Library Research and Innovation Report 50
15.
Hard disk drive
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The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a manner, meaning that individual blocks of data can be stored or retrieved in any order. HDDs are a type of storage, retaining stored data even when powered off. Introduced by IBM in 1956, HDDs became the dominant secondary storage device for computers by the early 1960s. Continuously improved, HDDs have maintained this position into the era of servers. More than 200 companies have produced HDDs historically, though after extensive industry consolidation most current units are manufactured by Seagate, Toshiba, as of 2016, HDD production is growing, although unit shipments and sales revenues are declining. While SSDs have higher cost per bit, SSDs are replacing HDDs where speed, power consumption, small size, the primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixes corresponding to powers of 1000, the two most common form factors for modern HDDs are 3. 5-inch, for desktop computers, and 2. 5-inch, primarily for laptops. HDDs are connected to systems by standard interface cables such as PATA, SATA, Hard disk drives were introduced in 1956, as data storage for an IBM real-time transaction processing computer and were developed for use with general-purpose mainframe and minicomputers. The first IBM drive, the 350 RAMAC in 1956, was approximately the size of two medium-sized refrigerators and stored five million six-bit characters on a stack of 50 disks. In 1962 the IBM350 RAMAC disk storage unit was superseded by the IBM1301 disk storage unit, cylinder-mode read/write operations were supported, and the heads flew about 250 micro-inches above the platter surface. Motion of the head array depended upon a binary system of hydraulic actuators which assured repeatable positioning. The 1301 cabinet was about the size of three home refrigerators placed side by side, storing the equivalent of about 21 million eight-bit bytes, access time was about a quarter of a second. Also in 1962, IBM introduced the model 1311 disk drive, users could buy additional packs and interchange them as needed, much like reels of magnetic tape. Later models of removable pack drives, from IBM and others, became the norm in most computer installations, non-removable HDDs were called fixed disk drives. Some high-performance HDDs were manufactured with one head per track so that no time was lost physically moving the heads to a track, known as fixed-head or head-per-track disk drives they were very expensive and are no longer in production. In 1973, IBM introduced a new type of HDD code-named Winchester and its primary distinguishing feature was that the disk heads were not withdrawn completely from the stack of disk platters when the drive was powered down. Instead, the heads were allowed to land on an area of the disk surface upon spin-down
16.
Flash memory
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Flash memory is electronic non-volatile computer storage medium that can be electrically erased and reprogrammed. Toshiba developed flash memory from EEPROM in the early 1980s and introduced it to the market in 1984, the two main types of flash memory are named after the NAND and NOR logic gates. The individual flash memory cells exhibit internal characteristics similar to those of the corresponding gates, where EPROMs had to be completely erased before being rewritten, NAND-type flash memory may be written and read in blocks which are generally much smaller than the entire device. NOR-type flash allows a machine word to be written—to an erased location—or read independently. The NAND type operates primarily in memory cards, USB flash drives, solid-state drives, NAND or NOR flash memory is also often used to store configuration data in numerous digital products, a task previously made possible by EEPROM or battery-powered static RAM. One key disadvantage of flash memory is that it can endure a relatively small number of write cycles in a specific block. In addition to being non-volatile, flash memory offers fast read access times, although flash memory is technically a type of EEPROM, the term EEPROM is generally used to refer specifically to non-flash EEPROM which is erasable in small blocks, typically bytes. Because erase cycles are slow, the block sizes used in flash memory erasing give it a significant speed advantage over non-flash EEPROM when writing large amounts of data. As of 2013, flash memory costs much less than byte-programmable EEPROM and had become the dominant memory type wherever a system required a significant amount of non-volatile solid-state storage, Flash memory was invented by Fujio Masuoka while working for Toshiba circa 1980. According to Toshiba, the flash was suggested by Masuokas colleague, Shōji Ariizumi. Masuoka and colleagues presented the invention at the IEEE1984 International Electron Devices Meeting held in San Francisco, Intel Corporation saw the massive potential of the invention and introduced the first commercial NOR type flash chip in 1988. NOR-based flash has long erase and write times, but provides full address and data buses, allowing random access to any memory location. This makes it a replacement for older read-only memory chips. Its endurance may be from as little as 100 erase cycles for a flash memory, to a more typical 10,000 or 100,000 erase cycles. NOR-based flash was the basis of early flash-based removable media, CompactFlash was originally based on it, however, the I/O interface of NAND flash does not provide a random-access external address bus. Rather, data must be read on a basis, with typical block sizes of hundreds to thousands of bits. This makes NAND flash unsuitable as a replacement for program ROM. In this regard, NAND flash is similar to other data storage devices, such as hard disks and optical media
17.
DVD
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DVD is a digital optical disc storage format invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. The medium can store any kind of data and is widely used for software. DVDs offer higher capacity than compact discs while having the same dimensions. Pre-recorded DVDs are mass-produced using molding machines that physically stamp data onto the DVD, such discs are a form of DVD-ROM because data can only be read and not written or erased. Blank recordable DVD discs can be recorded using a DVD recorder. Rewritable DVDs can be recorded and erased many times, DVDs containing other types of information may be referred to as DVD data discs. The OED also states that in 1995, The companies said the name of the format will simply be DVD. Toshiba had been using the name ‘digital video disk’, but that was switched to ‘digital versatile disk’ after computer companies complained that it left out their applications, Digital versatile disc is the explanation provided in a DVD Forum Primer from 2000 and in the DVD Forums mission statement. There were several formats developed for recording video on optical discs before the DVD, Optical recording technology was invented by David Paul Gregg and James Russell in 1958 and first patented in 1961. A consumer optical disc data format known as LaserDisc was developed in the United States and it used much larger discs than the later formats. CD Video used analog video encoding on optical discs matching the established standard 120 mm size of audio CDs, Video CD became one of the first formats for distributing digitally encoded films in this format, in 1993. In the same year, two new optical disc formats were being developed. By the time of the launches for both formats in January 1995, the MMCD nomenclature had been dropped, and Philips and Sony were referring to their format as Digital Video Disc. Representatives from the SD camp asked IBM for advice on the system to use for their disc. Alan E. Bell, a researcher from IBMs Almaden Research Center, got that request and this group was referred to as the Technical Working Group, or TWG. On August 14,1995, an ad hoc group formed from five computer companies issued a release stating that they would only accept a single format. The TWG voted to both formats unless the two camps agreed on a single, converged standard. They recruited Lou Gerstner, president of IBM, to pressure the executives of the warring factions, as a result, the DVD specification provided a storage capacity of 4.7 GB for a single-layered, single-sided disc and 8.5 GB for a dual-layered, single-sided disc
18.
Hertz
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The hertz is the unit of frequency in the International System of Units and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide proof of the existence of electromagnetic waves. Hertz are commonly expressed in SI multiples kilohertz, megahertz, gigahertz, kilo means thousand, mega meaning million, giga meaning billion and tera for trillion. Some of the units most common uses are in the description of waves and musical tones, particularly those used in radio-. It is also used to describe the speeds at which computers, the hertz is equivalent to cycles per second, i. e. 1/second or s −1. In English, hertz is also used as the plural form, as an SI unit, Hz can be prefixed, commonly used multiples are kHz, MHz, GHz and THz. One hertz simply means one cycle per second,100 Hz means one hundred cycles per second, and so on. The unit may be applied to any periodic event—for example, a clock might be said to tick at 1 Hz, the rate of aperiodic or stochastic events occur is expressed in reciprocal second or inverse second in general or, the specific case of radioactive decay, becquerels. Whereas 1 Hz is 1 cycle per second,1 Bq is 1 aperiodic radionuclide event per second, the conversion between a frequency f measured in hertz and an angular velocity ω measured in radians per second is ω =2 π f and f = ω2 π. This SI unit is named after Heinrich Hertz, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, the hertz is named after the German physicist Heinrich Hertz, who made important scientific contributions to the study of electromagnetism. The name was established by the International Electrotechnical Commission in 1930, the term cycles per second was largely replaced by hertz by the 1970s. One hobby magazine, Electronics Illustrated, declared their intention to stick with the traditional kc. Mc. etc. units, sound is a traveling longitudinal wave which is an oscillation of pressure. Humans perceive frequency of waves as pitch. Each musical note corresponds to a frequency which can be measured in hertz. An infants ear is able to perceive frequencies ranging from 20 Hz to 20,000 Hz, the range of ultrasound, infrasound and other physical vibrations such as molecular and atomic vibrations extends from a few femtoHz into the terahertz range and beyond. Electromagnetic radiation is described by its frequency—the number of oscillations of the perpendicular electric and magnetic fields per second—expressed in hertz. Radio frequency radiation is measured in kilohertz, megahertz, or gigahertz
19.
MacOS
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Within the market of desktop, laptop and home computers, and by web usage, it is the second most widely used desktop OS after Microsoft Windows. Launched in 2001 as Mac OS X, the series is the latest in the family of Macintosh operating systems, Mac OS X succeeded classic Mac OS, which was introduced in 1984, and the final release of which was Mac OS9 in 1999. An initial, early version of the system, Mac OS X Server 1.0, was released in 1999, the first desktop version, Mac OS X10.0, followed in March 2001. In 2012, Apple rebranded Mac OS X to OS X. Releases were code named after big cats from the release up until OS X10.8 Mountain Lion. Beginning in 2013 with OS X10.9 Mavericks, releases have been named after landmarks in California, in 2016, Apple rebranded OS X to macOS, adopting the nomenclature that it uses for their other operating systems, iOS, watchOS, and tvOS. The latest version of macOS is macOS10.12 Sierra, macOS is based on technologies developed at NeXT between 1985 and 1997, when Apple acquired the company. The X in Mac OS X and OS X is pronounced ten, macOS shares its Unix-based core, named Darwin, and many of its frameworks with iOS, tvOS and watchOS. A heavily modified version of Mac OS X10.4 Tiger was used for the first-generation Apple TV, Apple also used to have a separate line of releases of Mac OS X designed for servers. Beginning with Mac OS X10.7 Lion, the functions were made available as a separate package on the Mac App Store. Releases of Mac OS X from 1999 to 2005 can run only on the PowerPC-based Macs from the time period, Mac OS X10.5 Leopard was released as a Universal binary, meaning the installer disc supported both Intel and PowerPC processors. In 2009, Apple released Mac OS X10.6 Snow Leopard, in 2011, Apple released Mac OS X10.7 Lion, which no longer supported 32-bit Intel processors and also did not include Rosetta. All versions of the system released since then run exclusively on 64-bit Intel CPUs, the heritage of what would become macOS had originated at NeXT, a company founded by Steve Jobs following his departure from Apple in 1985. There, the Unix-like NeXTSTEP operating system was developed, and then launched in 1989 and its graphical user interface was built on top of an object-oriented GUI toolkit using the Objective-C programming language. This led Apple to purchase NeXT in 1996, allowing NeXTSTEP, then called OPENSTEP, previous Macintosh operating systems were named using Arabic numerals, e. g. Mac OS8 and Mac OS9. The letter X in Mac OS Xs name refers to the number 10 and it is therefore correctly pronounced ten /ˈtɛn/ in this context. However, a common mispronunciation is X /ˈɛks/, consumer releases of Mac OS X included more backward compatibility. Mac OS applications could be rewritten to run natively via the Carbon API, the consumer version of Mac OS X was launched in 2001 with Mac OS X10.0. Reviews were variable, with praise for its sophisticated, glossy Aqua interface
20.
Mac OS X Snow Leopard
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Mac OS X Snow Leopard is the seventh major release of Mac OS X, Apples desktop and server operating system for Macintosh computers. Snow Leopard was publicly unveiled on June 8,2009 at the Apple Worldwide Developers Conference, on August 28,2009, it was released worldwide, and was made available for purchase from Apples website and its retail stores at the price of US$29 for a single-user license. As a result of the low price, initial sales of Snow Leopard were significantly higher than that of its predecessors, the release of Snow Leopard came nearly two years after the introduction of Mac OS X Leopard, the second longest time span between successive Mac OS X releases. Unlike those of versions of Mac OS X, the goals of Snow Leopard were improved performance, greater efficiency. Addition of new features was not a primary consideration, its name signified its goal to be a refinement of the previous OS X version. Much of the software in Mac OS X was extensively rewritten for this release in order to take advantage fully of modern Macintosh hardware, new programming frameworks, such as OpenCL, were created, allowing software developers to use graphics cards in their applications. This is also the first Mac OS release since System 7.1.1 that does not support Macs using PowerPC processors, as Apple now intends to focus on its current line of Intel-based products. As support for Rosetta was dropped in OS X Lion, Snow Leopard is the last version of Mac OS X that is able to run PowerPC-only applications, Snow Leopard was succeeded by Mac OS X Lion on July 20,2011.6.6 update. Snow Leopard is the last release of Mac OS X to support the 32-bit Intel Core Solo, Apple states the following basic Snow Leopard system requirements are, Mac computer with an Intel processor. Yonah processors such as Core Solo and Core Duo can run only 32-bit applications, later x86-64 architecture processors such as Core 2 Duo, Core i5, single-user licenses and family pack licenses for up to five computers are available. For qualifying Mac computers bought after June 8,2009, Apple offered a discounted price through their up to date program provided that orders were faxed or postmarked by December 26,2009. These licenses differ in their requirements for pre-installed versions of Mac OS X, Leopard Upgrade, a Family Pack Upgrade for Mac OS X Leopard license is also mentioned as a subset of the Leopard Upgrade. Single Use, places no restriction on which version of Mac OS X should already be installed, used for the non-upgrade and Mac Box Set versions of Snow Leopard. Subject to the terms and conditions of this License and you are granted a limited non-exclusive license to install, use and run one copy of the Apple Software on a single Apple-branded computer at a time. Family Pack, identical to the Single Use license in this respect and it is not entirely clear which license is offered with the retail version of Snow Leopard. Mac OS X Snow Leopard is intended to be a release aimed to refine the feature set, expand the technological capabilities of the operating system. Many of the changes involve how the works in the background and are not intended to be seen by the user. For example, the Finder application was rewritten in the Cocoa application programming interface
21.
Microsoft Windows
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Microsoft Windows is a metafamily of graphical operating systems developed, marketed, and sold by Microsoft. It consists of families of operating systems, each of which cater to a certain sector of the computing industry with the OS typically associated with IBM PC compatible architecture. Active Windows families include Windows NT, Windows Embedded and Windows Phone, defunct Windows families include Windows 9x, Windows 10 Mobile is an active product, unrelated to the defunct family Windows Mobile. Microsoft introduced an operating environment named Windows on November 20,1985, Microsoft Windows came to dominate the worlds personal computer market with over 90% market share, overtaking Mac OS, which had been introduced in 1984. Apple came to see Windows as an encroachment on their innovation in GUI development as implemented on products such as the Lisa. On PCs, Windows is still the most popular operating system, however, in 2014, Microsoft admitted losing the majority of the overall operating system market to Android, because of the massive growth in sales of Android smartphones. In 2014, the number of Windows devices sold was less than 25% that of Android devices sold and this comparison however may not be fully relevant, as the two operating systems traditionally target different platforms. As of September 2016, the most recent version of Windows for PCs, tablets, smartphones, the most recent versions for server computers is Windows Server 2016. A specialized version of Windows runs on the Xbox One game console, Microsoft, the developer of Windows, has registered several trademarks each of which denote a family of Windows operating systems that target a specific sector of the computing industry. It now consists of three operating system subfamilies that are released almost at the time and share the same kernel. Windows, The operating system for personal computers, tablets. The latest version is Windows 10, the main competitor of this family is macOS by Apple Inc. for personal computers and Android for mobile devices. Windows Server, The operating system for server computers, the latest version is Windows Server 2016. Unlike its clients sibling, it has adopted a strong naming scheme, the main competitor of this family is Linux. Windows PE, A lightweight version of its Windows sibling meant to operate as an operating system, used for installing Windows on bare-metal computers. The latest version is Windows PE10.0.10586.0, Windows Embedded, Initially, Microsoft developed Windows CE as a general-purpose operating system for every device that was too resource-limited to be called a full-fledged computer. The following Windows families are no longer being developed, Windows 9x, Microsoft now caters to the consumers market with Windows NT. Windows Mobile, The predecessor to Windows Phone, it was a mobile operating system
22.
Computer memory
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In computing, memory refers to the computer hardware devices involved to store information for immediate use in a computer, it is synonymous with the term primary storage. Computer memory operates at a speed, for example random-access memory, as a distinction from storage that provides slow-to-access program and data storage. If needed, contents of the memory can be transferred to secondary storage. An archaic synonym for memory is store, there are two main kinds of semiconductor memory, volatile and non-volatile. Examples of non-volatile memory are flash memory and ROM, PROM, EPROM and EEPROM memory, most semiconductor memory is organized into memory cells or bistable flip-flops, each storing one bit. Flash memory organization includes both one bit per cell and multiple bits per cell. The memory cells are grouped into words of fixed word length, each word can be accessed by a binary address of N bit, making it possible to store 2 raised by N words in the memory. This implies that processor registers normally are not considered as memory, since they only store one word, typical secondary storage devices are hard disk drives and solid-state drives. In the early 1940s, memory technology oftenly permit a capacity of a few bytes, the next significant advance in computer memory came with acoustic delay line memory, developed by J. Presper Eckert in the early 1940s. Delay line memory would be limited to a capacity of up to a few hundred thousand bits to remain efficient, two alternatives to the delay line, the Williams tube and Selectron tube, originated in 1946, both using electron beams in glass tubes as means of storage. Using cathode ray tubes, Fred Williams would invent the Williams tube, the Williams tube would prove more capacious than the Selectron tube and less expensive. The Williams tube would prove to be frustratingly sensitive to environmental disturbances. Efforts began in the late 1940s to find non-volatile memory, jay Forrester, Jan A. Rajchman and An Wang developed magnetic core memory, which allowed for recall of memory after power loss. Magnetic core memory would become the dominant form of memory until the development of transistor-based memory in the late 1960s, developments in technology and economies of scale have made possible so-called Very Large Memory computers. The term memory when used with reference to computers generally refers to Random Access Memory or RAM, volatile memory is computer memory that requires power to maintain the stored information. Most modern semiconductor volatile memory is either static RAM or dynamic RAM, SRAM retains its contents as long as the power is connected and is easy for interfacing, but uses six transistors per bit. SRAM is not worthwhile for desktop system memory, where DRAM dominates, SRAM is commonplace in small embedded systems, which might only need tens of kilobytes or less. Forthcoming volatile memory technologies that aim at replacing or competing with SRAM and DRAM include Z-RAM and A-RAM, non-volatile memory is computer memory that can retain the stored information even when not powered
23.
Random-access memory
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Random-access memory is a form of computer data storage which stores frequently used program instructions to increase the general speed of a system. A random-access memory device allows data items to be read or written in almost the same amount of time irrespective of the location of data inside the memory. RAM contains multiplexing and demultiplexing circuitry, to connect the lines to the addressed storage for reading or writing the entry. Usually more than one bit of storage is accessed by the same address, in todays technology, random-access memory takes the form of integrated circuits. RAM is normally associated with types of memory, where stored information is lost if power is removed. Other types of non-volatile memories exist that allow access for read operations. These include most types of ROM and a type of memory called NOR-Flash. Integrated-circuit RAM chips came into the market in the early 1970s, with the first commercially available DRAM chip, early computers used relays, mechanical counters or delay lines for main memory functions. Ultrasonic delay lines could only reproduce data in the order it was written, drum memory could be expanded at relatively low cost but efficient retrieval of memory items required knowledge of the physical layout of the drum to optimize speed. Latches built out of vacuum tube triodes, and later, out of transistors, were used for smaller and faster memories such as registers. Such registers were relatively large and too costly to use for large amounts of data, the first practical form of random-access memory was the Williams tube starting in 1947. It stored data as electrically charged spots on the face of a cathode ray tube, since the electron beam of the CRT could read and write the spots on the tube in any order, memory was random access. The capacity of the Williams tube was a few hundred to around a thousand bits, but it was smaller, faster. In fact, rather than the Williams tube memory being designed for the SSEM, magnetic-core memory was invented in 1947 and developed up until the mid-1970s. It became a form of random-access memory, relying on an array of magnetized rings. By changing the sense of each rings magnetization, data could be stored with one bit stored per ring, since every ring had a combination of address wires to select and read or write it, access to any memory location in any sequence was possible. Magnetic core memory was the form of memory system until displaced by solid-state memory in integrated circuits. Data was stored in the capacitance of each transistor, and had to be periodically refreshed every few milliseconds before the charge could leak away
24.
Floppy disk
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Floppy disks are read and written by a floppy disk drive. Floppy disks, initially as 8-inch media and later in 5¼-inch and 3½-inch sizes, were a form of data storage and exchange from the mid-1970s into the mid-2000s. These formats are usually handled by older equipment and these disks and associated drives were produced and improved upon by IBM and other companies such as Memorex, Shugart Associates, and Burroughs Corporation. The term floppy disk appeared in print as early as 1970, in 1976, Shugart Associates introduced the first 5¼-inch FDD. By 1978 there were more than 10 manufacturers producing such FDDs, there were competing floppy disk formats, with hard- and soft-sector versions and encoding schemes such as FM, MFM and GCR. The 5¼-inch format displaced the 8-inch one for most applications, the most common capacity of the 5¼-inch format in DOS-based PCs was 360 kB and in 1984 IBM introduced the 1.2 MB dual-sided floppy disk along with its PC-AT model. IBM started using the 720 kB double-density 3½-inch microfloppy disk on its Convertible laptop computer in 1986 and these disk drives could be added to older PC models. In 1988 IBM introduced a drive for 2.88 MB DSED diskettes in its top-of-the-line PS/2 models, throughout the early 1980s, limitations of the 5¼-inch format became clear. Originally designed to be practical than the 8-inch format, it was itself too large, as the quality of recording media grew. A number of solutions were developed, with drives at 2-, 2½-, 3-, 3½-, the large market share of the 5¼-inch format made it difficult for these new formats to gain significant market share. A variant on the Sony design, introduced in 1982 by a number of manufacturers, was then rapidly adopted. By the end of the 1980s, 5¼-inch disks had been superseded by 3½-inch disks, by the mid-1990s, 5¼-inch drives had virtually disappeared, as the 3½-inch disk became the predominant floppy disk. Floppy disks became ubiquitous during the 1980s and 1990s in their use with computers to distribute software, transfer data. Before hard disks became affordable to the population, floppy disks were often used to store a computers operating system. Most home computers from that period have a primary OS and BASIC stored as ROM, by the early 1990s, the increasing software size meant large packages like Windows or Adobe Photoshop required a dozen disks or more. In 1996, there were a five billion standard floppy disks in use. Then, distribution of packages was gradually replaced by CD-ROMs, DVDs. External USB-based floppy disk drives are available, many modern systems provide firmware support for booting from such drives
25.
Pixel
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The address of a pixel corresponds to its physical coordinates. LCD pixels are manufactured in a grid, and are often represented using dots or squares. Each pixel is a sample of an image, more samples typically provide more accurate representations of the original. The intensity of each pixel is variable, in color imaging systems, a color is typically represented by three or four component intensities such as red, green, and blue, or cyan, magenta, yellow, and black. The word pixel is based on a contraction of pix and el, the word pixel was first published in 1965 by Frederic C. Billingsley of JPL, to describe the elements of video images from space probes to the Moon. Billingsley had learned the word from Keith E. McFarland, at the Link Division of General Precision in Palo Alto, McFarland said simply it was in use at the time. The word is a combination of pix, for picture, the word pix appeared in Variety magazine headlines in 1932, as an abbreviation for the word pictures, in reference to movies. By 1938, pix was being used in reference to pictures by photojournalists. The concept of a picture element dates to the earliest days of television, some authors explain pixel as picture cell, as early as 1972. In graphics and in image and video processing, pel is often used instead of pixel, for example, IBM used it in their Technical Reference for the original PC. A pixel is generally thought of as the smallest single component of a digital image, however, the definition is highly context-sensitive. For example, there can be printed pixels in a page, or pixels carried by electronic signals, or represented by digital values, or pixels on a display device, or pixels in a digital camera. This list is not exhaustive and, depending on context, synonyms include pel, sample, byte, bit, dot, Pixels can be used as a unit of measure such as,2400 pixels per inch,640 pixels per line, or spaced 10 pixels apart. For example, a high-quality photographic image may be printed with 600 ppi on a 1200 dpi inkjet printer, even higher dpi numbers, such as the 4800 dpi quoted by printer manufacturers since 2002, do not mean much in terms of achievable resolution. The more pixels used to represent an image, the closer the result can resemble the original, the number of pixels in an image is sometimes called the resolution, though resolution has a more specific definition.3 megapixels. The pixels, or color samples, that form an image may or may not be in one-to-one correspondence with screen pixels. In computing, a composed of pixels is known as a bitmapped image or a raster image
26.
Bitmap
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In computing, a bitmap is a mapping from some domain to bits, that is, values which are zero or one. It is also called a bit array or bitmap index, in computer graphics, when the domain is a rectangle a bitmap gives a way to store a binary image, that is, an image in which each pixel is either black or white. The more general term refers to a map of pixels. Often bitmap is used for this as well, in some contexts, the term bitmap implies one bit per pixel, while pixmap is used for images with multiple bits per pixel. A bitmap is a type of organization or image file format used to store digital images. The term bitmap comes from the computer programming terminology, meaning just a map of bits, now, along with pixmap, it commonly refers to the similar concept of a spatially mapped array of pixels. Raster images in general may be referred to as bitmaps or pixmaps, whether synthetic or photographic, besides BMP, other file formats that store literal bitmaps include InterLeaved Bitmap, Portable Bitmap, X Bitmap, and Wireless Application Protocol Bitmap. Similarly, most other file formats, such as JPEG, TIFF, PNG, and GIF, also store bitmap images. In typical uncompressed bitmaps, image pixels are stored with a color depth of 1,4,8,16,24,32,48. Pixels of 8 bits and fewer can represent either grayscale or indexed color. An alpha channel may be stored in a bitmap, where it is similar to a grayscale bitmap, or in a fourth channel that, for example. The bits representing the bitmap pixels may be packed or unpacked, depending on the color depth, a pixel in the picture will occupy at least n/8 bytes, where n is the bit depth. In the formula above, header size and color palette size, due to effects of row padding to align each row start to a storage unit boundary such as a word, additional bytes may be needed. They called these device-independent bitmaps or DIBs, and the format for them is called DIB file format or BMP file format. According to Microsoft support, A device-independent bitmap is a used to define device-independent bitmaps in various color resolutions. The main purpose of DIBs is to allow bitmaps to be moved from one device to another, a DIB is an external format, in contrast to a device-dependent bitmap, which appears in the system as a bitmap object. A DIB is normally transported in metafiles, BMP files, here, device independent refers to the format, or storage arrangement, and should not be confused with device-independent color. The X Window System uses a similar XBM format for black-and-white images, numerous other uncompressed bitmap file formats are in use, though most not widely
27.
Color depth
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For consumer video standards, such as High Efficiency Video Coding, the bit depth specifies the number of bits used for each color component. When referring to a pixel the concept can be defined as bits per pixel, which specifies the number of bits used. When referring to a component the concept can be defined as bits per component, bits per channel, bits per color. Color depth is one aspect of color representation, expressing how finely levels of color can be expressed. The definition of both color precision and gamut is accomplished with a color encoding specification which assigns a code value to a location in a color space. Comparison, same image on five different color depths, different looks, but also different file sizes. With the relatively low color depth, the value is typically a number representing the index into a color map or palette. The colors available in the palette itself may be fixed by the hardware or modifiable within the limits of the hardware, modifiable palettes are sometimes referred to as pseudocolor palettes. 1-bit color, monochrome, often black and white, compact Macintoshes, 2-bit color, CGA, gray-scale early NeXTstation, color Macintoshes, Atari ST. 12-bit color, some Silicon Graphics systems, Color NeXTstation systems, for example, in the ZX Spectrum, the picture is stored in a two-color format, but these two colors can be separately defined for each rectangular block of 8x8 pixels. A very limited but true direct color system, there are 3 bits for each of the R and G components, the normal human eye is less sensitive to the blue component than to the red or green, so it is assigned one bit less than the others. Used, amongst others, in the MSX2 system series of computers in the early to mid 1990s, do not confuse with an indexed color depth of 8bpp. High color supports 15/16-bit for three RGB colors, in 16-bit direct color, there can be 4 bits for each of the R, G, and B components, plus optionally 4 bits for alpha, enabling 4,096 different colors with 16 levels of transparency. Or in some systems there can be 5 bits per color component and 1 bit of alpha, or there can be 5 bits for red,6 bits for green and these color depths are sometimes used in small devices with a color display, such as mobile telephones. Variants with 5 or more bits per component are sometimes called high color. More expensive LCDs can display 24-bit or greater color depth, true color supports 24-bit for three RGB colors. Usually, true color is defined to mean 256 shades of red, green, the human eye can discriminate up to ten million colors. Color processing in the eye occurs through retinal cone cells which are of three types, although not corresponding to red, green and blue hues, true color can also refer to an RGB display-mode that does not need a color look-up table
28.
JPEG
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JPEG is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between size and image quality. JPEG typically achieves 10,1 compression with little loss in image quality. JPEG compression is used in a number of file formats. These format variations are not distinguished, and are simply called JPEG. The term JPEG is an initialism/acronym for the Joint Photographic Experts Group, the MIME media type for JPEG is image/jpeg, except in older Internet Explorer versions, which provides a MIME type of image/pjpeg when uploading JPEG images. JPEG files usually have an extension of. jpg or. jpeg. JPEG/JFIF supports a maximum size of 65, 535×65,535 pixels. JPEG stands for Joint Photographic Experts Group, the name of the committee created the JPEG standard. The Joint stood for ISO TC97 WG8 and CCITT SGVIII, in 1987 ISO TC97 became ISO/IEC JTC1 and in 1992 CCITT became ITU-T. Currently on the JTC1 side JPEG is one of two sub-groups of ISO/IEC Joint Technical Committee 1, Subcommittee 29, Working Group 1 – titled as Coding of still pictures, on the ITU-T side ITU-T SG16 is the respective body. The original JPEG group was organized in 1986, issuing the first JPEG standard in 1992, which was approved in September 1992 as ITU-T Recommendation T.81 and in 1994 as ISO/IEC 10918-1. The JPEG standard specifies the codec, which defines how an image is compressed into a stream of bytes and decompressed back into an image, the Exif and JFIF standards define the commonly used file formats for interchange of JPEG-compressed images. JPEG standards are formally named as Information technology – Digital compression, ISO/IEC10918 consists of the following parts, Ecma International TR/98 specifies the JPEG File Interchange Format, the first edition was published in June 2009. The JPEG compression algorithm is at its best on photographs and paintings of scenes with smooth variations of tone. For web usage, where the amount of used for an image is important. JPEG/Exif is also the most common format saved by digital cameras, on the other hand, JPEG may not be as well suited for line drawings and other textual or iconic graphics, where the sharp contrasts between adjacent pixels can cause noticeable artifacts. Such images may be saved in a lossless graphics format such as TIFF, GIF, PNG
