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Exa is a decimal unit prefix in the metric system denoting 10^{18} or 1000000000000000000. It was added as an SI prefix to the International System of Units (SI) in 1975,^{ [1] } and has the unit symbol E.
A unit prefix is a specifier or mnemonic that is prepended to units of measurement to indicate multiples or fractions of the units. Units of various sizes are commonly formed by the use of such prefixes. The prefixes of the metric system, such as kilo and milli, represent multiplication by powers of ten. In information technology it is common to use binary prefixes, which are based on powers of two. Historically, many prefixes have been used or proposed by various sources, but only a narrow set has been recognised by standards organisations.
The metric system is an internationally recognised decimalised system of measurement. It is in widespread use, and where it is adopted, it is the only or most common system of weights and measures. It is now known as the International System of Units (SI). It is used to measure everyday things such as the mass of a sack of flour, the height of a person, the speed of a car, and the volume of fuel in its tank. It is also used in science, industry and trade.
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, which are the second, metre, kilogram, ampere, kelvin, mole, candela, and 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 also specifies names for 22 derived units, such as lumen and watt, for other common physical quantities.
Exa comes from the Ancient Greek ἕξhéx, used as a prefix ἑξάhexá, meaning six (like hexa), because it is equal to 1000^{6}.
The Ancient Greek language includes the forms of Greek used in Ancient Greece and the ancient world from around the 9th century BCE to the 6th century CE. It is often roughly divided into the Archaic period, Classical period, and Hellenistic period. It is antedated in the second millennium BCE by Mycenaean Greek and succeeded by medieval Greek.
Examples:
The exabyte is a multiple of the unit byte for digital information. In the International System of Units (SI), the prefix exa indicates multiplication by the sixth power of 1000 (10^{18}). Therefore, one exabyte is one quintillion bytes (short scale). The unit symbol for the exabyte is EB.
In physics, the electronvolt is a unit of energy equal to exactly 1.602176634×10^{−19} joules in SI units.
The joule is a derived unit of energy in the International System of Units. It is equal to the energy transferred to an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre. It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889).

This list contains selected positive numbers in increasing order, including counts of things, dimensionless quantity and probabilities. Each number is given a name in the short scale, which is used in Englishspeaking countries, as well as a name in the long scale, which is used in some of the countries that do not have English as their national language.
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 common use today are decadic, historically there have been a number of binary metric prefixes as well. Each prefix has a unique symbol that is prepended to the unit symbol. The prefix kilo, for example, may be added to gram to indicate multiplication by one thousand: one kilogram is equal to one thousand grams. 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.
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.
A centimetre or centimeter is a unit of length in the metric system, equal to one hundredth of a metre, centi being the SI prefix for a factor of 1/100. The centimetre was the base unit of length in the now deprecated centimetre–gram–second (CGS) system of units.
A globular cluster is a spherical collection of stars that orbit a galactic core, as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes, and relatively high stellar densities toward their centers. The name of this category of star cluster is derived from the Latin, globulus—a small sphere. A globular cluster is sometimes known, more simply, as a globular.
Mega is a unit prefix in metric systems of units denoting a factor of one million (10^{6} or 1000000). It has the unit symbol M. It was confirmed for use in the International System of Units (SI) in 1960. Mega comes from Ancient Greek: μέγας, romanized: megas, lit. 'great'.
The parsec (symbol: pc) is a unit of length used to measure large distances to astronomical objects outside the Solar System. A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond, which corresponds to 648000/π astronomical units. One parsec is equal to about 3.26 lightyears or 31 trillion kilometres (31×10^{12} km) or 19 trillion miles (19×10^{12} mi). The nearest star, Proxima Centauri, is about 1.3 parsecs (4.2 lightyears) from the Sun. Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the Sun.
A supercomputer is a computer with a high level of performance compared to a generalpurpose computer. The performance of a supercomputer is commonly measured in floatingpoint operations per second (FLOPS) instead of million instructions per second (MIPS). Since 2017, there are supercomputers which can perform over a hundred quadrillion FLOPS. Since November 2017, all of the world's fastest 500 supercomputers run Linuxbased operating systems. Additional research is being conducted in China, the United States, the European Union, Taiwan and Japan to build even faster, more powerful and more technologically superior exascale supercomputers.
In computing, floating point operations per second is a measure of computer performance, useful in fields of scientific computations that require floatingpoint calculations. For such cases it is a more accurate measure than measuring instructions per second.
The exbibyte (symbol EiB) is 2^{60} bytes of digital information. It is one of a set of units with binary prefixes defined by the International Electrotechnical Commission (IEC).
Messier 4 or M4 is a globular cluster in the constellation of Scorpius. It was discovered by Philippe Loys de Chéseaux in 1745 and catalogued by Charles Messier in 1764. It was the first globular cluster in which individual stars were resolved.
Messier 107 or M107, also known as NGC 6171, is a very loose globular cluster in the constellation Ophiuchus, and is the last globular cluster in the Messier Catalogue. It was discovered by Pierre Méchain in April 1782, then independently by William Herschel in 1793. Herschel described it as a "globular cluster of stars, large, very rich, very much compressed, round, well resolved, clearly consisting of stars". It was not until 1947 that Helen Sawyer Hogg added it and three other objects discovered by Méchain to the list of Messier objects. The cluster is located 2.5° south and slightly west of the star Zeta Ophiuchi.
The exabit is a multiple of the unit bit for digital information or computer storage. The prefix exa (symbol E) is defined in the International System of Units (SI) as a multiplier of 10^{18} (1 quintillion, short scale), and therefore
The exbibit is a multiple of the bit, a unit of digital information storage, prefixed by the standardsbased multiplier exbi (symbol Ei), a binary prefix meaning 2^{60}. The unit symbol of the exbibit is Eibit.
Omega Centauri is a globular cluster in the constellation of Centaurus that was first identified as a nonstellar object by Edmond Halley in 1677. Located at a distance of 15,800 lightyears, it is the largest globular cluster in the Milky Way at a diameter of roughly 150 lightyears. It is estimated to contain approximately 10 million stars and a total mass equivalent to 4 million solar masses, making it the most massive globular cluster of the Milky Way.
Messier 56 is a globular cluster in the constellation Lyra. It was discovered by Charles Messier on January 19, 1779. The cluster is located almost midway along an imaginary line between Albireo and Sulafat. It is a challenge to find with large (50–80 mm) binoculars, appearing as a slightly fuzzy star. The cluster can be resolved using a telescope with an aperture of 8 in (20 cm) or larger.
47 Tucanae, 47 Tuc is a globular cluster located in the constellation Tucana. It is about 4.0 ± 0.35 kpc (13,000 ± 1,100 ly) away from Earth, and 120 light years across. 47 Tuc can be seen with the naked eye, with an apparent magnitude of 4.1. It appears about 50 arcminutes across. Due to its far southern location, 18° from the south celestial pole, it was not catalogued by European astronomers until the 1750s, when the cluster was first identified by NicolasLouis de Lacaille from South Africa.
The TOP500 project ranks and details the 500 most powerful nondistributed computer systems in the world. The project was started in 1993 and publishes an updated list of the supercomputers twice a year. The first of these updates always coincides with the International Supercomputing Conference in June, and the second is presented at the ACM/IEEE Supercomputing Conference in November. The project aims to provide a reliable basis for tracking and detecting trends in highperformance computing and bases rankings on HPL, a portable implementation of the highperformance LINPACK benchmark written in Fortran for distributedmemory computers.
This list compares various amounts of computing power in instructions per second organized by order of magnitude in FLOPS.
NGC 5286 is a globular cluster of stars located some 35,900 light years away in the constellation Centaurus. At this distance, the light from the cluster has undergone reddening from interstellar gas and dust equal to E(B – V) = 0.24 magnitude in the UBV photometric system. The cluster lies 4 arcminutes north of the nakedeye star M Centauri. It was discovered by Scottish astronomer James Dunlop, active in Australia, and listed in his 1827 catalog.
bestfit dynamical distance D=4.8±0.3 kpc ... consistent with the canonical value 5.0±0.2 kpc obtained by photometric methodsCheck date values in:
date=
(help)The International Bureau of Weights and Measures is an intergovernmental organization that was established by the Metre Convention, through which member states act together on matters related to measurement science and measurement standards. The organisation is usually referred to by its French initialism, BIPM. The BIPM's secretariat and formal meetings are housed in the organizations headquarters in Sèvres, France.
The International Standard Book Number (ISBN) is a numeric commercial book identifier which is intended to be unique. Publishers purchase ISBNs from an affiliate of the International ISBN Agency.
Look up exa in Wiktionary, the free dictionary. 