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In the 9th century, the rise of the cult of the Apostle James in Santiago de Compostela gave Galicia a particular symbolic importance among Christians, an importance it would hold throughout the Reconquista. As the Middle Ages went on, Santiago became a major pilgrim destination and the Way of Saint James (Camiño de Santiago) a major pilgrim road, a route for the propagation of Romanesque art and the words and music of the troubadors. During the 10th and 11th centuries, a period during which Galician nobility become related to the royal family, Galicia was at times headed by its own native kings, while Vikings (locally known as Leodemanes or Lordomanes) occasionally raided the coasts. The Towers of Catoira (Pontevedra) were built as a system of fortifications to prevent and stop the Viking raids on Santiago de Compostela.
In 1063, Ferdinand I of Castile divided his realm among his sons, and the Kingdom of Galicia was granted to Garcia II of Galicia. In 1072, it was forcibly annexed by Garcia's brother Alfonso VI of León; from that time Galicia was united with the Kingdom of León under the same monarchs. In the 13th century Alfonso X of Castile standardized the Castilian language and made it the language of court and government. Nevertheless, in his Kingdom of Galicia the Galician language was the only language spoken, and the most used in government and legal uses, as well as in literature.
On the other hand, the lack of an effective royal justice system in the Kingdom led to the social conflict known as the Guerras Irmandiñas ('Wars of the brotherhoods'), when leagues of peasants and burghers, with the support of a number of knights, noblemen, and under legal protection offered by the remote king, toppled many of the castles of the Kingdom and briefly drove the noblemen into Portugal and Castile. Soon after, in the late 15th century, in the dynastic conflict between Isabella I of Castile and Joanna La Beltraneja, part of the Galician aristocracy supported Joanna. After Isabella's victory, she initiated an administrative and political reform which the chronicler Jeronimo Zurita defined as "doma del Reino de Galicia": 'It was then when the taming of Galicia began, because not just the local lords and knights, but all the people of that nation were the ones against the others very bold and warlike'. These reforms, while establishing a local government and tribunal (the Real Audiencia del Reino de Galicia) and bringing the nobleman under submission, also brought most Galician monasteries and institutions under Castilian control, in what has been criticized as a process of centralisation. At the same time the kings began to call the Xunta or Cortes of the Kingdom of Galicia, an assembly of deputies or representatives of the cities of the Kingdom, to ask for monetary and military contributions. This assembly soon developed into the voice and legal representation of the Kingdom, and the depositary of its will and laws.
The modern period of the kingdom of Galicia began with the murder or defeat of some of the most powerful Galician lords, such as Pedro Álvarez de Sotomayor, called Pedro Madruga, and Rodrigo Henriquez Osorio, at the hands of the Castilian armies sent to Galicia between the years 1480 and 1486. Isabella I of Castile, considered a usurper by many Galician nobles, eradicated all armed resistance and definitively established the royal power of the Castilian monarchy. Fearing a general revolt, the monarchs ordered the banishing of the rest of the great lords like Pedro de Bolaño, Diego de Andrade or Lope Sánchez de Moscoso, among others.
The establishment of the Santa Hermandad in 1480, and of the Real Audiencia del Reino de Galicia in 1500—a tribunal and executive body directed by the Governor-Captain General as a direct representative of the King—implied initially the submission of the Kingdom to the Crown, after a century of unrest and fiscal insubordination. As a result, from 1480 to 1520 the Kingdom of Galicia contributed more than 10% of the total earnings of the Crown of Castille, including the Americas, well over its economic relevance. Like the rest of Spain, the 16th century was marked by population growth up to 1580, when the simultaneous wars with the Netherlands, France and England hampered Galicia's Atlantic commerce, which consisted mostly in the exportation of sardines, wood, and some cattle and wine.
From that moment Galicia, which participated to a minor extent in the American expansion of the Spanish Empire, found itself at the center of the Atlantic wars fought by Spain against the French and the Protestant powers of England and the Netherlands, whose privateers attacked the coastal areas, but major assaults were not common as the coastline was difficult and the harbors easily defended. The most famous assaults were upon the city of Vigo by Sir Francis Drake in 1585 and 1589, and the siege of A Coruña in 1589 by the English Armada. Galicia also suffered occasional slave raids by Barbary pirates, but not as frequently as the Mediterranean coastal areas. The most famous Barbary attack was the bloody sack of the town of Cangas in 1617. At the time, the king's petitions for money and troops became more frequent, due to the human and economic exhaustion of Castile; the Junta of the Kingdom of Galicia (the local Cortes or representative assembly) was initially receptive to these petitions, raising large sums, accepting the conscription of the men of the kingdom, and even commissioning a new naval squadron which was sustained with the incomes of the Kingdom.
After the rupture of the wars with Portugal and Catalonia, the Junta changed its attitude, this time due to the exhaustion of Galicia, now involved not just in naval or oversea operations, but also in an exhausting war with the Portuguese, war which produced thousands of casualties and refugees and was heavily disturbing to the local economy and commerce. So, in the second half of the 17th century the Junta frequently denied or considerably reduced the initial petitions of the monarch, and though the tension didn't rise to the levels experienced in Portugal or Catalonia, there were frequent urban mutinies and some voices even asked for the secession of the Kingdom of Galicia.
In the early 20th century came another turn toward nationalist politics with Solidaridad Gallega (1907–1912) modeled on Solidaritat Catalana in Catalonia. Solidaridad Gallega failed, but in 1916 Irmandades da Fala (Brotherhood of the Language) developed first as a cultural association but soon as a full-blown nationalist movement. Vicente Risco and Ramón Otero Pedrayo were outstanding cultural figures of this movement, and the magazine Nós ('Us'), founded 1920, its most notable cultural institution, Lois Peña Novo the outstanding political figure.
Galicia was spared the worst of the fighting in that war: it was one of the areas where the initial coup attempt at the outset of the war was successful, and it remained in Nationalist (Franco's army's) hands throughout the war. While there were no pitched battles, there was repression and death: all political parties were abolished, as were all labor unions and Galician nationalist organizations as the Seminario de Estudos Galegos. Galicia's statute of autonomy was annulled (as were those of Catalonia and the Basque provinces once those were conquered). According to Carlos Fernández Santander, at least 4,200 people were killed either extrajudicially or after summary trials, among them republicans, communists, Galician nationalists, socialists and anarchists. Victims included the civil governors of all four Galician provinces; Juana Capdevielle, the wife of the governor of A Coruña; mayors such as Ánxel Casal of Santiago de Compostela, of the Partido Galeguista; prominent socialists such as Jaime Quintanilla in Ferrol and Emilio Martínez Garrido in Vigo; Popular Front deputies Antonio Bilbatúa, José Miñones, Díaz Villamil, Ignacio Seoane, and former deputy Heraclio Botana); soldiers who had not joined the rebellion, such as Generals Rogelio Caridad Pita and Enrique Salcedo Molinuevo and Admiral Antonio Azarola; and the founders of the PG, Alexandre Bóveda and Víctor Casas, as well as other professionals akin to republicans and nationalists, as the journalist Manuel Lustres Rivas or physician Luis Poza Pastrana. Many others were forced to escape into exile, or were victims of other reprisals and removed from their jobs and positions.
General Francisco Franco — himself a Galician from Ferrol — ruled as dictator from the civil war until his death in 1975. Franco's centralizing regime suppressed any official use of the Galician language, including the use of Galician names for newborns, although its everyday oral use was not forbidden. Among the attempts at resistance were small leftist guerrilla groups such as those led by José Castro Veiga ("El Piloto") and Benigno Andrade ("Foucellas"), both of whom were ultimately captured and executed. In the 1960s, ministers such as Manuel Fraga Iribarne introduced some reforms allowing technocrats affiliated with Opus Dei to modernize administration in a way that facilitated capitalist economic development. However, for decades Galicia was largely confined to the role of a supplier of raw materials and energy to the rest of Spain, causing environmental havoc and leading to a wave of migration to Venezuela and to various parts of Europe. Fenosa, the monopolistic supplier of electricity, built hydroelectric dams, flooding many Galician river valleys.
As part of the transition to democracy upon the death of Franco in 1975, Galicia regained its status as an autonomous region within Spain with the Statute of Autonomy of 1981, which begins, "Galicia, historical nationality, is constituted as an Autonomous Community to access to its self-government, in agreement with the Spanish Constitution and with the present Statute (...)". Varying degrees of nationalist or independentist sentiment are evident at the political level. The Bloque Nacionalista Galego or BNG, is a conglomerate of left-wing parties and individuals that claims Galician political status as a nation.
From 1990 to 2005, Manuel Fraga, former minister and ambassador in the Franco dictature, presided over the Galician autonomous government, the Xunta de Galicia. Fraga was associated with the Partido Popular ('People's Party', Spain's main national conservative party) since its founding. In 2002, when the oil tanker Prestige sank and covered the Galician coast in oil, Fraga was accused by the grassroots movement Nunca Mais ("Never again") of having been unwilling to react. In the 2005 Galician elections, the 'People's Party' lost its absolute majority, though remaining (barely) the largest party in the parliament, with 43% of the total votes. As a result, power passed to a coalition of the Partido dos Socialistas de Galicia (PSdeG) ('Galician Socialists' Party'), a federal sister-party of Spain's main social-democratic party, the Partido Socialista Obrero Español (PSOE, 'Spanish Socialist Workers Party') and the nationalist Bloque Nacionalista Galego (BNG). As the senior partner in the new coalition, the PSdeG nominated its leader, Emilio Perez Touriño, to serve as Galicia's new president, with Anxo Quintana, the leader of BNG, as its vice president.
Galicia has a surface area of 29,574 square kilometres (11,419 sq mi). Its northernmost point, at 43°47′N, is Estaca de Bares (also the northernmost point of Spain); its southernmost, at 41°49′N, is on the Portuguese border in the Baixa Limia-Serra do Xurés Natural Park. The easternmost longitude is at 6°42′W on the border between the province of Ourense and the Castilian-Leonese province of Zamora) its westernmost at 9°18′W, reached in two places: the A Nave Cape in Fisterra (also known as Finisterre), and Cape Touriñán, both in the province of A Coruña.
Topographically, a remarkable feature of Galicia is the presence of many firth-like inlets along the coast, estuaries that were drowned with rising sea levels after the ice age. These are called rías and are divided into the smaller Rías Altas ("High Rías"), and the larger Rías Baixas ("Low Rías"). The Rías Altas include Ribadeo, Foz, Viveiro, Barqueiro, Ortigueira, Cedeira, Ferrol, Betanzos, A Coruña, Corme e Laxe and Camariñas. The Rías Baixas, found south of Fisterra, include Corcubión, Muros e Noia, Arousa, Pontevedra and Vigo. The Rías Altas can sometimes refer only to those east of Estaca de Bares, with the others being called Rías Medias ("Intermediate Rías").
All along the Galician coast are various archipelagos near the mouths of the rías. These archipelagos provide protected deepwater harbors and also provide habitat for seagoing birds. A 2007 inventory estimates that the Galician coast has 316 archipelagos, islets, and freestanding rocks. Among the most important of these are the archipelagos of Cíes, Ons, and Sálvora. Together with Cortegada Island, these make up the Atlantic Islands of Galicia National Park. Other significant islands are Islas Malveiras, Islas Sisargas, and, the largest and holding the largest population, Arousa Island.
Galicia is quite mountainous, a fact which has contributed to isolate the rural areas, hampering communications, most notably in the inland. The main mountain range is the Macizo Galaico (Serra do Eixe, Serra da Lastra, Serra do Courel), also known as Macizo Galaico-Leonés, located in the eastern parts, bordering with Castile and León. Noteworthy mountain ranges are O Xistral (northern Lugo), the Serra dos Ancares (on the border with León and Asturias), O Courel (on the border with León), O Eixe (the border between Ourense and Zamora), Serra de Queixa (in the center of Ourense province), O Faro (the border between Lugo and Pontevedra), Cova da Serpe (border of Lugo and A Coruña), Montemaior (A Coruña), Montes do Testeiro, Serra do Suído, and Faro de Avión (between Pontevedra and Ourense); and, to the south, A Peneda, O Xurés and O Larouco, all on the border of Ourense and Portugal.
Galicia is poetically known as the "country of the thousand rivers" ("o país dos mil ríos"). The largest and most important of these rivers is the Minho, known as O Pai Miño (Father Minho), 307.5 km (191.1 mi) long and discharging 419 m3 (548 cu yd) per second, with its affluent the Sil, which has created a spectacular canyon. Most of the rivers in the inland are tributaries of this fluvial system, which drains some 17,027 km2 (6,574 sq mi). Other rivers run directly into the Atlantic Ocean as Lérez or the Cantabrian Sea, most of them having short courses. Only the Navia, Ulla, Tambre, and Limia have courses longer than 100 km (62 mi).
Deforestation and forest fires are a problem in many areas, as is the continual spread of the eucalyptus tree, a species imported from Australia, actively promoted by the paper industry since the mid-20th century. Galicia is one of the more forested areas of Spain, but the majority of Galicia's plantations, usually growing eucalyptus or pine, lack any formal management. Massive eucalyptus, especially Eucalyptus globulus plantation, began in the Francisco Franco era, largely on behalf of the paper company Empresa Nacional de Celulosas de España (ENCE) in Pontevedra, which wanted it for its pulp. Wood products figure significantly in Galicia's economy. Apart from tree plantations Galicia is also notable for the extensive surface occupied by meadows used for animal husbandry, especially cattle , an important activity. Hydroelectric development in most rivers has been a serious concern for local conservationists during the last decades.
The animals most often thought of as being "typical" of Galicia are the livestock raised there. The Galician horse is native to the region, as is the Galician Blond cow and the domestic fowl known as the galiña de Mos. The latter is an endangered species, although it is showing signs of a comeback since 2001. Galicia's woodlands and mountains are home to rabbits, hares, wild boars, and roe deer, all of which are popular with hunters. Several important bird migration routes pass through Galicia, and some of the community's relatively few environmentally protected areas are Special Protection Areas (such as on the Ría de Ribadeo) for these birds. From a domestic point of view, Galicia has been credited for author Manuel Rivas as the "land of one million cows". Galician Blond and Holstein cattle coexist on meadows and farms.
Being located on the Atlantic coastline, Galicia has a very mild climate for the latitude and the marine influence affects most of the province to various degrees. In comparison to similar latitudes on the other side of the Atlantic, winters are exceptionally mild, with consistently heavy rainfall. Snow is rare due to temperatures rarely dropping below freezing. The warmest coastal station of Pontevedra has a yearly mean temperature of 14.8 °C (58.6 °F). Ourense located somewhat inland is only slightly warmer with 14.9 °C (58.8 °F). Due to its exposed north-westerly location, the climate is still very cool by Spanish standards. In coastal areas summers are temperered, averaging around 25 °C (77 °F) in Vigo. Temperatures are further cooler in A Coruña, with a subdued 22.8 °C (73.0 °F) normal. Temperatures do however soar in inland areas such as Ourense, where days above 30 °C (86 °F) are very regular.
The lands of Galicia are ascribed to two different areas in the Köppen climate classification: a south area (roughly, the province of Ourense and Pontevedra) with tendencies to have some summer drought, classified as a warm-summer Mediterranean climate (Csb), with mild temperatures and rainfall usual throughout the year; and the western and northern coastal regions, the provinces of Lugo and A Coruña, which are characterized by their Oceanic climate (Cfb), with a more uniform precipitation distribution along the year, and milder summers. However, precipitation in southern coastal areas are often classified as oceanic since the averages remain significantly higher than a typical mediterranean climate.
As an example, Santiago de Compostela, the political capital city, has an average of 129 rainy days and 1,362 millimetres (53.6 in) per year (with just 17 rainy days in the three summer months) and 2,101 sunlight hours per year, with just 6 days with frosts per year. But the colder city of Lugo, to the east, has an average of 1,759 sunlight hours per year, 117 days with precipitations (> 1 mm) totalling 901.54 millimetres (35.5 in), and 40 days with frosts per year. The more mountainous parts of the provinces of Ourense and Lugo receive significant snowfall during the winter months. The sunniest city is Pontevedra with 2,223 sunny hours per year.
Galicia is further divided into 53 comarcas, 315 municipalities (93 in A Coruña, 67 in Lugo, 92 in Ourense, 62 in Pontevedra) and 3,778 parishes. Municipalities are divided into parishes, which may be further divided into aldeas ("hamlets") or lugares ("places"). This traditional breakdown into such small areas is unusual when compared to the rest of Spain. Roughly half of the named population entities of Spain are in Galicia, which occupies only 5.8 percent of the country's area. It is estimated that Galicia has over a million named places, over 40,000 of them being communities.
In comparison to the other regions of Spain, the major economic benefit of Galicia is its fishing Industry. Galicia is a land of economic contrast. While the western coast, with its major population centers and its fishing and manufacturing industries, is prosperous and increasing in population, the rural hinterland — the provinces of Ourense and Lugo — is economically dependent on traditional agriculture, based on small landholdings called minifundios. However, the rise of tourism, sustainable forestry and organic and traditional agriculture are bringing other possibilities to the Galician economy without compromising the preservation of the natural resources and the local culture.
Galicia was late to catch the tourism boom that has swept Spain in recent decades, but the coastal regions (especially the Rías Baixas and Santiago de Compostela) are now significant tourist destinations and are especially popular with visitors from other regions in Spain, where the majority of tourists come from. In 2007, 5.7 million tourists visited Galicia, an 8% growth over the previous year, and part of a continual pattern of growth in this sector. 85% of tourists who visit Galicia visit Santiago de Compostela. Tourism constitutes 12% of Galician GDP and employs about 12% of the regional workforce.
The most important Galician fishing port is the Port of Vigo; It is one of the world's leading fishing ports, second only to Tokyo, with an annual catch worth 1,500 million euros. In 2007 the port took in 732,951 metric tons (721,375 long tons; 807,940 short tons) of fish and seafood, and about 4,000,000 metric tons (3,900,000 long tons; 4,400,000 short tons) of other cargoes. Other important ports are Ferrol, A Coruña, and the smaller ports of Marín and Vilagarcía de Arousa, as well as important recreational ports in Pontevedra and Burela. Beyond these, Galicia has 120 other organized ports.
Within Galicia are the Autopista AP-9 from Ferrol to Vigo and the Autopista AP-53 (also known as AG-53, because it was initially built by the Xunta de Galicia) from Santiago to Ourense. Additional roads under construction include Autovía A-54 from Santiago de Compostela to Lugo, and Autovía A-56 from Lugo to Ourense. The Xunta de Galicia has built roads connecting comarcal capitals, such as the aforementioned AG-53, Autovía AG-55 connecting A Coruña to Carballo or AG-41 connecting Pontevedra to Sanxenxo.
The first railway line in Galicia was inaugurated 15 September 1873. It ran from O Carril, Vilagarcía de Arousa to Cornes, Conxo, Santiago de Compostela. A second line was inaugurated in 1875, connecting A Coruña and Lugo. In 1883, Galicia was first connected by rail to the rest of Spain, by way of O Barco de Valdeorras. Galicia today has roughly 1,100 kilometres (680 mi) of rail lines. Several 1,668 mm (5 ft 5 21⁄32 in) Iberian gauge lines operated by Adif and Renfe Operadora connect all the important Galician cities. A 1,000 mm (3 ft 3 3⁄8 in) metre gauge line operated by FEVE connects Ferrol to Ribadeo and Oviedo. The only electrified line is the Ponferrada-Monforte de Lemos-Ourense-Vigo line. Several high-speed rail lines are under construction. Among these are the Olmedo-Zamora-Galicia high-speed rail line that opened partly in 2011, and the AVE Atlantic Axis route, which will connect all of the major Galician Atlantic coast cities A Coruña, Santiago de Compostela, Pontevedra and Vigo to Portugal. Another projected AVE line will connect Ourense to Pontevedra and Vigo.
The rapid increase of population of A Coruña, Vigo and to a lesser degree other major Galician cities, like Ourense, Pontevedra or Santiago de Compostela during the years that followed the Spanish Civil War during the mid-20th century occurred as the rural population declined: many villages and hamlets of the four provinces of Galicia disappeared or nearly disappeared during the same period. Economic development and mechanization of agriculture resulted in the fields being abandoned, and most of the population has moving to find jobs in the main cities. The number of people working in the Tertiary and Quaternary sectors of the economy has increased significantly.
Spanish was nonetheless the only official language in Galicia for more than four centuries. Over the many centuries of Castilian domination, Galician faded from day-to-day use in urban areas. The period since the re-establishment of democracy in Spain—in particular since the Lei de Normalización Lingüística ("Law of Linguistic Normalization", Ley 3/1983, 15 June 1983)—represents the first time since the introduction of mass education that a generation has attended school in Galician (Spanish is also still taught in Galician schools).
Nowadays, Galician is resurgent, though in the cities it remains a "second language" for most. According to a 2001 census, 99.16 percent of the populace of Galicia understand the language, 91.04 percent speak it, 68.65 percent read it and 57.64 percent write it. The first two numbers (understanding and speaking) remain roughly the same as a decade earlier; the latter two (reading and writing) both show enormous gains: a decade earlier, only 49.3 percent of the population could read Galician, and only 34.85 percent could write it. This fact can be easily explained because of the impossibility of teaching Galician during the Francisco Franco era, so older people speak the language but have no written competence. Galician is the highest-percentage spoken language in its region among the regional languages of Spain.
The earliest known document in Galician-Portuguese dates from 1228. The Foro do bo burgo do Castro Caldelas was granted by Alfonso IX of León to the town of Burgo, in Castro Caldelas, after the model of the constitutions of the town of Allariz. A distinct Galician Literature emerged during the Middle Ages: In the 13th century important contributions were made to the romance canon in Galician-Portuguese, the most notable those by the troubadour Martín Codax, the priest Airas Nunes, King Denis of Portugal and King Alfonso X of Castile, Alfonso O Sabio ("Alfonso the Wise"), the same monarch who began the process of establishing the hegemony of Castilian. During this period, Galician-Portuguese was considered the language of love poetry in the Iberian Romance linguistic culture. The names and memories of Codax and other popular cultural figures are well preserved in modern Galicia and, despite the long period of Castilian linguistic domination, these names are again household words.
Christianity is the most widely practised religion in Galicia, as it has been since its introduction in Late Antiquity, although it lived alongside the old Gallaeci religion for a few centuries. Today about 73% of Galicians identify themselves as Christians. The largest form of Christianity practised in the present day is Catholicism, though only 20% of the population described themselves as active members. The Catholic Church in Galicia has had its primatial seat in Santiago de Compostela since the 12th century.
Since the Middle Ages, the Galician Catholic Church has been organized into five ecclesiastical dioceses (Lugo, Ourense, Santiago de Compostela, Mondoñedo-Ferrol and Tui-Vigo). While these may have coincided with contemporary 15th-century civil provinces, they no longer have the same boundaries as the modern civil provincial divisions. The church is led by one archbishop and four bishops. Moreover, of five dioceses, Galicia is divided between 163 districts and 3,792 parishes, a few of which are governed by administrators, the remainder by parish priests.
Hundreds of ancient standing stone monuments like dolmens, menhirs and megalithics Tumulus were erected during the prehistoric period in Galicia, amongst the best-known are the dolmens of Dombate, Corveira, Axeitos of Pedra da Arca, menhirs like the "Lapa de Gargñáns". From the Iron Age, Galicia has a rich heritage based mainly on a great number of Hill forts, few of them excavated like Baroña, Sta. Tegra, San Cibrao de Lás and Formigueiros among others. With the introduction of Ancient Roman architecture there was a development of basilicas, castra, city walls, cities, villas, Roman temples, Roman roads, and the Roman bridge of Ponte Vella. It was the Romans who founded some of the first cities in Galicia like Lugo and Ourense. Perhaps the best-known examples are the Roman Walls of Lugo and the Tower of Hercules in A Coruña.
The patron saint of Galicia is Saint James the Greater, whose body was discovered – according to the Catholic tradition – in 814 near Compostela. After that date, the relics of Saint James became an extraordinary centre of pilgrimage and from the 9th century have been kept in the heart of the church – the modern-day cathedral – dedicated to him. There are many other Galician and associated saints; some of the best-known are: Saint Ansurius, Saint Rudesind, Saint Mariña of Augas Santas, Saint Senorina, Trahamunda and Froilan.
In northern Galicia, the A Coruña-Ferrol metropolitan area has become increasingly dominant in terms of population. The population of the city of A Coruña in 1900 was 43,971. The population of the rest of the province including the City and Naval Station of nearby Ferrol and Santiago de Compostela was 653,556. A Coruña's growth occurred after the Spanish Civil War at the same speed as other major Galician cities, but it was the arrival of democracy in Spain after the death of Francisco Franco when A Coruña left all the other Galician cities behind.
Galicia's inhabitants are known as Galicians (Galician: galegos, Spanish: gallegos). For well over a century Galicia has grown more slowly than the rest of Spain, due largely to emigration to Latin America and to other parts of Spain. Sometimes Galicia has lost population in absolute terms. In 1857, Galicia had Spain's densest population and constituted 11.5% of the national population. As of 2007, only 6.1% of the Spanish population resides in the autonomous community. This is due to an exodus of Galician people since the 19th century, first to South America and later to Central Europe.
The Galician road network includes autopistas and autovías connecting the major cities, as well as national and secondary roads to the rest of the municipalities. The Autovía A-6 connects A Coruña and Lugo to Madrid, entering Galicia at Pedrafita do Cebreiro. The Autovía A-52 connects O Porriño, Ourense and Benavente, and enters Galicia at A Gudiña. Two more autovías are under construction. Autovía A-8 enters Galicia on the Cantabrian coast, and ends in Baamonde (Lugo province). Autovía A-76 enters Galicia in Valdeorras; it is an upgrade of the existing N-120 to Ourense and Vigo.
The modern English word green comes from the Middle English and Anglo-Saxon word grene, from the same Germanic root as the words "grass" and "grow". It is the color of living grass and leaves and as a result is the color most associated with springtime, growth and nature. By far the largest contributor to green in nature is chlorophyll, the chemical by which plants photosynthesize and convert sunlight into chemical energy. Many creatures have adapted to their green environments by taking on a green hue themselves as camouflage. Several minerals have a green color, including the emerald, which is colored green by its chromium content.
In surveys made in Europe and the United States, green is the color most commonly associated with nature, life, health, youth, spring, hope and envy. In Europe and the U.S. green is sometimes associated with death (green has several seemingly contrary associations), sickness, or the devil, but in China its associations are very positive, as the symbol of fertility and happiness. In the Middle Ages and Renaissance, when the color of clothing showed the owner's social status, green was worn by merchants, bankers and the gentry, while red was the color of the nobility. The Mona Lisa by Leonardo da Vinci wears green, showing she is not from a noble family; the benches in the British House of Commons are green, while those in the House of Lords are red. Green is also the traditional color of safety and permission; a green light means go ahead, a green card permits permanent residence in the United States. It is the most important color in Islam. It was the color of the banner of Muhammad, and is found in the flags of nearly all Islamic countries, and represents the lush vegetation of Paradise. It is also often associated with the culture of Gaelic Ireland, and is a color of the flag of Ireland. Because of its association with nature, it is the color of the environmental movement. Political groups advocating environmental protection and social justice describe themselves as part of the Green movement, some naming themselves Green parties. This has led to similar campaigns in advertising, as companies have sold green, or environmentally friendly, products.
Thus, the languages mentioned above (Germanic, Romance, Slavic, Greek) have old terms for "green" which are derived from words for fresh, sprouting vegetation. However, comparative linguistics makes clear that these terms were coined independently, over the past few millennia, and there is no identifiable single Proto-Indo-European or word for "green". For example, the Slavic zelenъ is cognate with Sanskrit hari "yellow, ochre, golden". The Turkic languages also have jašɨl "green" or "yellowish green", compared to a Mongolian word for "meadow".
In some languages, including old Chinese, Thai, old Japanese, and Vietnamese, the same word can mean either blue or green. The Chinese character 青 (pronounced qīng in Mandarin, ao in Japanese, and thanh in Sino-Vietnamese) has a meaning that covers both blue and green; blue and green are traditionally considered shades of "青". In more contemporary terms, they are 藍 (lán, in Mandarin) and 綠 (lǜ, in Mandarin) respectively. Japanese also has two terms that refer specifically to the color green, 緑 (midori, which is derived from the classical Japanese descriptive verb midoru "to be in leaf, to flourish" in reference to trees) and グリーン (guriin, which is derived from the English word "green"). However, in Japan, although the traffic lights have the same colors that other countries have, the green light is described using the same word as for blue, "aoi", because green is considered a shade of aoi; similarly, green variants of certain fruits and vegetables such as green apples, green shiso (as opposed to red apples and red shiso) will be described with the word "aoi". Vietnamese uses a single word for both blue and green, xanh, with variants such as xanh da trời (azure, lit. "sky blue"), lam (blue), and lục (green; also xanh lá cây, lit. "leaf green").
"Green" in modern European languages corresponds to about 520–570 nm, but many historical and non-European languages make other choices, e.g. using a term for the range of ca. 450–530 nm ("blue/green") and another for ca. 530–590 nm ("green/yellow").[citation needed] In the comparative study of color terms in the world's languages, green is only found as a separate category in languages with the fully developed range of six colors (white, black, red, green, yellow, and blue), or more rarely in systems with five colors (white, red, yellow, green, and black/blue). (See distinction of green from blue) These languages have introduced supplementary vocabulary to denote "green", but these terms are recognizable as recent adoptions that are not in origin color terms (much like the English adjective orange being in origin not a color term but the name of a fruit). Thus, the Thai word เขียว besides meaning "green" also means "rank" and "smelly" and holds other unpleasant associations.
In the subtractive color system, used in painting and color printing, green is created by a combination of yellow and blue, or yellow and cyan; in the RGB color model, used on television and computer screens, it is one of the additive primary colors, along with red and blue, which are mixed in different combinations to create all other colors. On the HSV color wheel, also known as the RGB color wheel, the complement of green is magenta; that is, a color corresponding to an equal mixture of red and blue light (one of the purples). On a traditional color wheel, based on subtractive color, the complementary color to green is considered to be red.
In additive color devices such as computer displays and televisions, one of the primary light sources is typically a narrow-spectrum yellowish-green of dominant wavelength ~550 nm; this "green" primary is combined with an orangish-red "red" primary and a purplish-blue "blue" primary to produce any color in between – the RGB color model. A unique green (green appearing neither yellowish nor bluish) is produced on such a device by mixing light from the green primary with some light from the blue primary.
Lasers emitting in the green part of the spectrum are widely available to the general public in a wide range of output powers. Green laser pointers outputting at 532 nm (563.5 THz) are relatively inexpensive compared to other wavelengths of the same power, and are very popular due to their good beam quality and very high apparent brightness. The most common green lasers use diode pumped solid state (DPSS) technology to create the green light. An infrared laser diode at 808 nm is used to pump a crystal of neodymium-doped yttrium vanadium oxide (Nd:YVO4) or neodymium-doped yttrium aluminium garnet (Nd:YAG) and induces it to emit 281.76 THz (1064 nm). This deeper infrared light is then passed through another crystal containing potassium, titanium and phosphorus (KTP), whose non-linear properties generate light at a frequency that is twice that of the incident beam (563.5 THz); in this case corresponding to the wavelength of 532 nm ("green"). Other green wavelengths are also available using DPSS technology ranging from 501 nm to 543 nm. Green wavelengths are also available from gas lasers, including the helium–neon laser (543 nm), the Argon-ion laser (514 nm) and the Krypton-ion laser (521 nm and 531 nm), as well as liquid dye lasers. Green lasers have a wide variety of applications, including pointing, illumination, surgery, laser light shows, spectroscopy, interferometry, fluorescence, holography, machine vision, non-lethal weapons and bird control.
Many minerals provide pigments which have been used in green paints and dyes over the centuries. Pigments, in this case, are minerals which reflect the color green, rather that emitting it through luminescent or phosphorescent qualities. The large number of green pigments makes it impossible to mention them all. Among the more notable green minerals, however is the emerald, which is colored green by trace amounts of chromium and sometimes vanadium. Chromium(III) oxide (Cr2O3), is called chrome green, also called viridian or institutional green when used as a pigment. For many years, the source of amazonite's color was a mystery. Widely thought to have been due to copper because copper compounds often have blue and green colors, the blue-green color is likely to be derived from small quantities of lead and water in the feldspar. Copper is the source of the green color in malachite pigments, chemically known as basic copper(II) carbonate.
Verdigris is made by placing a plate or blade of copper, brass or bronze, slightly warmed, into a vat of fermenting wine, leaving it there for several weeks, and then scraping off and drying the green powder that forms on the metal. The process of making verdigris was described in ancient times by Pliny. It was used by the Romans in the murals of Pompeii, and in Celtic medieval manuscripts as early as the 5th century AD. It produced a blue-green which no other pigment could imitate, but it had drawbacks; it was unstable, it could not resist dampness, it did not mix well with other colors, it could ruin other colors with which it came into contact., and it was toxic. Leonardo da Vinci, in his treatise on painting, warned artists not to use it. It was widely used in miniature paintings in Europe and Persia in the 16th and 17th centuries. Its use largely ended in the late 19th century, when it was replaced by the safer and more stable chrome green. Viridian, also called chrome green, is a pigment made with chromium oxide dihydrate, was patented in 1859. It became popular with painters, since, unlike other synthetic greens, it was stable and not toxic. Vincent van Gogh used it, along with Prussian blue, to create a dark blue sky with a greenish tint in his painting Cafe terrace at night.
There is no natural source for green food colorings which has been approved by the US Food and Drug Administration. Chlorophyll, the E numbers E140 and E141, is the most common green chemical found in nature, and only allowed in certain medicines and cosmetic materials. Quinoline Yellow (E104) is a commonly used coloring in the United Kingdom but is banned in Australia, Japan, Norway and the United States. Green S (E142) is prohibited in many countries, for it is known to cause hyperactivity, asthma, urticaria, and insomnia.
To create green sparks, fireworks use barium salts, such as barium chlorate, barium nitrate crystals, or barium chloride, also used for green fireplace logs. Copper salts typically burn blue, but cupric chloride (also known as "campfire blue") can also produce green flames. Green pyrotechnic flares can use a mix ratio 75:25 of boron and potassium nitrate. Smoke can be turned green by a mixture: solvent yellow 33, solvent green 3, lactose, magnesium carbonate plus sodium carbonate added to potassium chlorate.
Green is common in nature, as many plants are green because of a complex chemical known as chlorophyll, which is involved in photosynthesis. Chlorophyll absorbs the long wavelengths of light (red) and short wavelengths of light (blue) much more efficiently than the wavelengths that appear green to the human eye, so light reflected by plants is enriched in green. Chlorophyll absorbs green light poorly because it first arose in organisms living in oceans where purple halobacteria were already exploiting photosynthesis. Their purple color arose because they extracted energy in the green portion of the spectrum using bacteriorhodopsin. The new organisms that then later came to dominate the extraction of light were selected to exploit those portions of the spectrum not used by the halobacteria.
Animals typically use the color green as camouflage, blending in with the chlorophyll green of the surrounding environment. Green animals include, especially, amphibians, reptiles, and some fish, birds and insects. Most fish, reptiles, amphibians, and birds appear green because of a reflection of blue light coming through an over-layer of yellow pigment. Perception of color can also be affected by the surrounding environment. For example, broadleaf forests typically have a yellow-green light about them as the trees filter the light. Turacoverdin is one chemical which can cause a green hue in birds, especially. Invertebrates such as insects or mollusks often display green colors because of porphyrin pigments, sometimes caused by diet. This can causes their feces to look green as well. Other chemicals which generally contribute to greenness among organisms are flavins (lychochromes) and hemanovadin. Humans have imitated this by wearing green clothing as a camouflage in military and other fields. Substances that may impart a greenish hue to one's skin include biliverdin, the green pigment in bile, and ceruloplasmin, a protein that carries copper ions in chelation.
There is no green pigment in green eyes; like the color of blue eyes, it is an optical illusion; its appearance is caused by the combination of an amber or light brown pigmentation of the stroma, given by a low or moderate concentration of melanin, with the blue tone imparted by the Rayleigh scattering of the reflected light. Green eyes are most common in Northern and Central Europe. They can also be found in Southern Europe, West Asia, Central Asia, and South Asia. In Iceland, 89% of women and 87% of men have either blue or green eye color. A study of Icelandic and Dutch adults found green eyes to be much more prevalent in women than in men. Among European Americans, green eyes are most common among those of recent Celtic and Germanic ancestry, about 16%.
In Ancient Egypt green was the symbol of regeneration and rebirth, and of the crops made possible by the annual flooding of the Nile. For painting on the walls of tombs or on papyrus, Egyptian artists used finely-ground malachite, mined in the west Sinai and the eastern desert- A paintbox with malachite pigment was found inside the tomb of King Tutankhamun. They also used less expensive green earth pigment, or mixed yellow ochre and blue azurite. To dye fabrics green, they first colored them yellow with dye made from saffron and then soaked them in blue dye from the roots of the woad plant.
For the ancient Egyptians, green had very positive associations. The hieroglyph for green represented a growing papyrus sprout, showing the close connection between green, vegetation, vigor and growth. In wall paintings, the ruler of the underworld, Osiris, was typically portrayed with a green face, because green was the symbol of good health and rebirth. Palettes of green facial makeup, made with malachite, were found in tombs. It was worn by both the living and dead, particularly around the eyes, to protect them from evil. Tombs also often contained small green amulets in the shape of scarab beetles made of malachite, which would protect and give vigor to the deceased. It also symbolized the sea, which was called the "Very Green."
In Ancient Greece, green and blue were sometimes considered the same color, and the same word sometimes described the color of the sea and the color of trees. The philosopher Democritus described two different greens; cloron, or pale green, and prasinon, or leek green. Aristotle considered that green was located midway between black, symbolizing the earth, and white, symbolizing water. However, green was not counted among of the four classic colors of Greek painting; red, yellow, black and white, and is rarely found in Greek art.
The Romans had a greater appreciation for the color green; it was the color of Venus, the goddess of gardens, vegetables and vineyards.The Romans made a fine green earth pigment, which was widely used in the wall paintings of Pompeii, Herculaneum, Lyon, Vaison-la-Romaine, and other Roman cities. They also used the pigment verdigris, made by soaking copper plates in fermenting wine. By the Second Century AD, the Romans were using green in paintings, mosaics and glass, and there were ten different words in Latin for varieties of green.
Unfortunately for those who wanted or were required to wear green, there were no good vegetal green dyes which resisted washing and sunlight. Green dyes were made out of the fern, plantain, buckthorn berries, the juice of nettles and of leeks, the digitalis plant, the broom plant, the leaves of the fraxinus, or ash tree, and the bark of the alder tree, but they rapidly faded or changed color. Only in the 16th century was a good green dye produced, by first dyeing the cloth blue with woad, and then yellow with reseda luteola, also known as yellow-weed.
In the 18th and 19th century, green was associated with the romantic movement in literature and art. The French philosopher Jean-Jacques Rousseau celebrated the virtues of nature, The German poet and philosopher Goethe declared that green was the most restful color, suitable for decorating bedrooms. Painters such as John Constable and Jean-Baptiste-Camille Corot depicted the lush green of rural landscapes and forests. Green was contrasted to the smoky grays and blacks of the Industrial Revolution.
The late nineteenth century also brought the systematic study of color theory, and particularly the study of how complementary colors such as red and green reinforced each other when they were placed next to each other. These studies were avidly followed by artists such as Vincent van Gogh. Describing his painting, The Night Cafe, to his brother Theo in 1888, Van Gogh wrote: "I sought to express with red and green the terrible human passions. The hall is blood red and pale yellow, with a green billiard table in the center, and four lamps of lemon yellow, with rays of orange and green. Everywhere it is a battle and antithesis of the most different reds and greens."
Green can communicate safety to proceed, as in traffic lights. Green and red were standardized as the colors of international railroad signals in the 19th century. The first traffic light, using green and red gas lamps, was erected in 1868 in front of the Houses of Parliament in London. It exploded the following year, injuring the policeman who operated it. In 1912, the first modern electric traffic lights were put up in Salt Lake City, Utah. Red was chosen largely because of its high visibility, and its association with danger, while green was chosen largely because it could not be mistaken for red. Today green lights universally signal that a system is turned on and working as it should. In many video games, green signifies both health and completed objectives, opposite red.
Like other common colors, green has several completely opposite associations. While it is the color most associated by Europeans and Americans with good health, it is also the color most often associated with toxicity and poison. There was a solid foundation for this association; in the nineteenth century several popular paints and pigments, notably verdigris, vert de Schweinfurt and vert de Paris, were highly toxic, containing copper or arsenic.[d] The intoxicating drink absinthe was known as "the green fairy".
Many flags of the Islamic world are green, as the color is considered sacred in Islam (see below). The flag of Hamas, as well as the flag of Iran, is green, symbolizing their Islamist ideology. The 1977 flag of Libya consisted of a simple green field with no other characteristics. It was the only national flag in the world with just one color and no design, insignia, or other details. Some countries used green in their flags to represent their country's lush vegetation, as in the flag of Jamaica, and hope in the future, as in the flags of Portugal and Nigeria. The green cedar of Lebanon tree on the Flag of Lebanon officially represents steadiness and tolerance.
In the 1980s green became the color of a number of new European political parties organized around an agenda of environmentalism. Green was chosen for its association with nature, health, and growth. The largest green party in Europe is Alliance '90/The Greens (German: Bündnis 90/Die Grünen) in Germany, which was formed in 1993 from the merger of the German Green Party, founded in West Germany in 1980, and Alliance 90, founded during the Revolution of 1989–1990 in East Germany. In the 2009 federal elections, the party won 10.7% of the votes and 68 out of 622 seats in the Bundestag.
Roman Catholic and more traditional Protestant clergy wear green vestments at liturgical celebrations during Ordinary Time. In the Eastern Catholic Church, green is the color of Pentecost. Green is one of the Christmas colors as well, possibly dating back to pre-Christian times, when evergreens were worshiped for their ability to maintain their color through the winter season. Romans used green holly and evergreen as decorations for their winter solstice celebration called Saturnalia, which eventually evolved into a Christmas celebration. In Ireland and Scotland especially, green is used to represent Catholics, while orange is used to represent Protestantism. This is shown on the national flag of Ireland.
USB was designed to standardize the connection of computer peripherals (including keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters) to personal computers, both to communicate and to supply electric power. It has become commonplace on other devices, such as smartphones, PDAs and video game consoles. USB has effectively replaced a variety of earlier interfaces, such as serial and parallel ports, as well as separate power chargers for portable devices.
Unlike other data cables (e.g., Ethernet, HDMI), each end of a USB cable uses a different kind of connector; a Type-A or a Type-B. This kind of design was chosen to prevent electrical overloads and damaged equipment, as only the Type-A socket provides power. There are cables with Type-A connectors on both ends, but they should be used carefully. Therefore, in general, each of the different "sizes" requires four different connectors; USB cables have the Type-A and Type-B plugs, and the corresponding receptacles are on the computer or electronic device. In common practice, the Type-A connector is usually the full size, and the Type-B side can vary as needed.
Counter-intuitively, the "micro" size is the most durable from the point of designed insertion lifetime. The standard and mini connectors were designed for less than daily connections, with a design lifetime of 1,500 insertion-removal cycles. (Improved mini-B connectors have reached 5,000-cycle lifetimes.) Micro connectors were designed with frequent charging of portable devices in mind; not only is design lifetime of the connector improved to 10,000 cycles, but it was also redesigned to place the flexible contacts, which wear out sooner, on the easily replaced cable, while the more durable rigid contacts are located in the micro-USB receptacles. Likewise, the springy part of the retention mechanism (parts that provide required gripping force) were also moved into plugs on the cable side.
USB connections also come in five data transfer modes, in ascending order: Low Speed (1.0), Full Speed (1.0), High Speed (2.0), SuperSpeed (3.0), and SuperSpeed+ (3.1). High Speed is supported only by specifically designed USB 2.0 High Speed interfaces (that is, USB 2.0 controllers without the High Speed designation do not support it), as well as by USB 3.0 and newer interfaces. SuperSpeed is supported only by USB 3.0 and newer interfaces, and requires a connector and cable with extra pins and wires, usually distinguishable by the blue inserts in connectors.
A group of seven companies began the development of USB in 1994: Compaq, DEC, IBM, Intel, Microsoft, NEC, and Nortel. The goal was to make it fundamentally easier to connect external devices to PCs by replacing the multitude of connectors at the back of PCs, addressing the usability issues of existing interfaces, and simplifying software configuration of all devices connected to USB, as well as permitting greater data rates for external devices. A team including Ajay Bhatt worked on the standard at Intel; the first integrated circuits supporting USB were produced by Intel in 1995.
The original USB 1.0 specification, which was introduced in January 1996, defined data transfer rates of 1.5 Mbit/s "Low Speed" and 12 Mbit/s "Full Speed". Microsoft Windows 95, OSR 2.1 provided OEM support for the devices. The first widely used version of USB was 1.1, which was released in September 1998. The 12 Mbit/s data rate was intended for higher-speed devices such as disk drives, and the lower 1.5 Mbit/s rate for low data rate devices such as joysticks. Apple Inc.'s iMac was the first mainstream product with USB and the iMac's success popularized USB itself. Following Apple's design decision to remove all legacy ports from the iMac, many PC manufacturers began building legacy-free PCs, which led to the broader PC market using USB as a standard.
The new SuperSpeed bus provides a fourth transfer mode with a data signaling rate of 5.0 Gbit/s, in addition to the modes supported by earlier versions. The payload throughput is 4 Gbit/s[citation needed] (due to the overhead incurred by 8b/10b encoding), and the specification considers it reasonable to achieve around 3.2 Gbit/s (0.4 GB/s or 400 MB/s), which should increase with future hardware advances. Communication is full-duplex in SuperSpeed transfer mode; in the modes supported previously, by 1.x and 2.0, communication is half-duplex, with direction controlled by the host.
As with previous USB versions, USB 3.0 ports come in low-power and high-power variants, providing 150 mA and 900 mA respectively, while simultaneously transmitting data at SuperSpeed rates. Additionally, there is a Battery Charging Specification (Version 1.2 – December 2010), which increases the power handling capability to 1.5 A but does not allow concurrent data transmission. The Battery Charging Specification requires that the physical ports themselves be capable of handling 5 A of current[citation needed] but limits the maximum current drawn to 1.5 A.
A January 2013 press release from the USB group revealed plans to update USB 3.0 to 10 Gbit/s. The group ended up creating a new USB version, USB 3.1, which was released on 31 July 2013, introducing a faster transfer mode called SuperSpeed USB 10 Gbit/s, putting it on par with a single first-generation Thunderbolt channel. The new mode's logo features a "Superspeed+" caption (stylized as SUPERSPEED+). The USB 3.1 standard increases the data signaling rate to 10 Gbit/s in the USB 3.1 Gen2 mode, double that of USB 3.0 (referred to as USB 3.1 Gen1) and reduces line encoding overhead to just 3% by changing the encoding scheme to 128b/132b. The first USB 3.1 implementation demonstrated transfer speeds of 7.2 Gbit/s.
Developed at roughly the same time as the USB 3.1 specification, but distinct from it, the USB Type-C Specification 1.0 was finalized in August 2014 and defines a new small reversible-plug connector for USB devices. The Type-C plug connects to both hosts and devices, replacing various Type-A and Type-B connectors and cables with a standard meant to be future-proof, similar to Apple Lightning and Thunderbolt. The 24-pin double-sided connector provides four power/ground pairs, two differential pairs for USB 2.0 data bus (though only one pair is implemented in a Type-C cable), four pairs for high-speed data bus, two "sideband use" pins, and two configuration pins for cable orientation detection, dedicated biphase mark code (BMC) configuration data channel, and VCONN +5 V power for active cables. Type-A and Type-B adaptors and cables are required for older devices to plug into Type-C hosts. Adapters and cables with a Type-C receptacle are not allowed.[citation needed]
Full-featured USB Type-C cables are active, electronically marked cables that contain a chip with an ID function based on the configuration data channel and vendor-defined messages (VDMs) from the USB Power Delivery 2.0 specification. USB Type-C devices also support power currents of 1.5 A and 3.0 A over the 5 V power bus in addition to baseline 900 mA; devices can either negotiate increased USB current through the configuration line, or they can support the full Power Delivery specification using both BMC-coded configuration line and legacy BFSK-coded VBUS line.
The design architecture of USB is asymmetrical in its topology, consisting of a host, a multitude of downstream USB ports, and multiple peripheral devices connected in a tiered-star topology. Additional USB hubs may be included in the tiers, allowing branching into a tree structure with up to five tier levels. A USB host may implement multiple host controllers and each host controller may provide one or more USB ports. Up to 127 devices, including hub devices if present, may be connected to a single host controller. USB devices are linked in series through hubs. One hub—built into the host controller—is the root hub.
A physical USB device may consist of several logical sub-devices that are referred to as device functions. A single device may provide several functions, for example, a webcam (video device function) with a built-in microphone (audio device function). This kind of device is called a composite device. An alternative to this is compound device, in which the host assigns each logical device a distinctive address and all logical devices connect to a built-in hub that connects to the physical USB cable.
USB device communication is based on pipes (logical channels). A pipe is a connection from the host controller to a logical entity, found on a device, and named an endpoint. Because pipes correspond 1-to-1 to endpoints, the terms are sometimes used interchangeably. A USB device could have up to 32 endpoints (16 IN, 16 OUT), though it's rare to have so many. An endpoint is defined and numbered by the device during initialization (the period after physical connection called "enumeration") and so is relatively permanent, whereas a pipe may be opened and closed.
An endpoint of a pipe is addressable with a tuple (device_address, endpoint_number) as specified in a TOKEN packet that the host sends when it wants to start a data transfer session. If the direction of the data transfer is from the host to the endpoint, an OUT packet (a specialization of a TOKEN packet) having the desired device address and endpoint number is sent by the host. If the direction of the data transfer is from the device to the host, the host sends an IN packet instead. If the destination endpoint is a uni-directional endpoint whose manufacturer's designated direction does not match the TOKEN packet (e.g. the manufacturer's designated direction is IN while the TOKEN packet is an OUT packet), the TOKEN packet is ignored. Otherwise, it is accepted and the data transaction can start. A bi-directional endpoint, on the other hand, accepts both IN and OUT packets.
When a USB device is first connected to a USB host, the USB device enumeration process is started. The enumeration starts by sending a reset signal to the USB device. The data rate of the USB device is determined during the reset signaling. After reset, the USB device's information is read by the host and the device is assigned a unique 7-bit address. If the device is supported by the host, the device drivers needed for communicating with the device are loaded and the device is set to a configured state. If the USB host is restarted, the enumeration process is repeated for all connected devices.
High-speed USB 2.0 hubs contain devices called transaction translators that convert between high-speed USB 2.0 buses and full and low speed buses. When a high-speed USB 2.0 hub is plugged into a high-speed USB host or hub, it operates in high-speed mode. The USB hub then uses either one transaction translator per hub to create a full/low-speed bus routed to all full and low speed devices on the hub, or uses one transaction translator per port to create an isolated full/low-speed bus per port on the hub.
USB implements connections to storage devices using a set of standards called the USB mass storage device class (MSC or UMS). This was at first intended for traditional magnetic and optical drives and has been extended to support flash drives. It has also been extended to support a wide variety of novel devices as many systems can be controlled with the familiar metaphor of file manipulation within directories. The process of making a novel device look like a familiar device is also known as extension. The ability to boot a write-locked SD card with a USB adapter is particularly advantageous for maintaining the integrity and non-corruptible, pristine state of the booting medium.
Though most computers since mid-2004 can boot from USB mass storage devices, USB is not intended as a primary bus for a computer's internal storage. Buses such as Parallel ATA (PATA or IDE), Serial ATA (SATA), or SCSI fulfill that role in PC class computers. However, USB has one important advantage, in that it is possible to install and remove devices without rebooting the computer (hot-swapping), making it useful for mobile peripherals, including drives of various kinds (given SATA or SCSI devices may or may not support hot-swapping).
Firstly conceived and still used today for optical storage devices (CD-RW drives, DVD drives, etc.), several manufacturers offer external portable USB hard disk drives, or empty enclosures for disk drives. These offer performance comparable to internal drives, limited by the current number and types of attached USB devices, and by the upper limit of the USB interface (in practice about 30 MB/s for USB 2.0 and potentially 400 MB/s or more for USB 3.0). These external drives typically include a "translating device" that bridges between a drive's interface to a USB interface port. Functionally, the drive appears to the user much like an internal drive. Other competing standards for external drive connectivity include eSATA, ExpressCard, FireWire (IEEE 1394), and most recently Thunderbolt.
Media Transfer Protocol (MTP) was designed by Microsoft to give higher-level access to a device's filesystem than USB mass storage, at the level of files rather than disk blocks. It also has optional DRM features. MTP was designed for use with portable media players, but it has since been adopted as the primary storage access protocol of the Android operating system from the version 4.1 Jelly Bean as well as Windows Phone 8 (Windows Phone 7 devices had used the Zune protocol which was an evolution of MTP). The primary reason for this is that MTP does not require exclusive access to the storage device the way UMS does, alleviating potential problems should an Android program request the storage while it is attached to a computer. The main drawback is that MTP is not as well supported outside of Windows operating systems.
USB mice and keyboards can usually be used with older computers that have PS/2 connectors with the aid of a small USB-to-PS/2 adapter. For mice and keyboards with dual-protocol support, an adaptor that contains no logic circuitry may be used: the hardware in the USB keyboard or mouse is designed to detect whether it is connected to a USB or PS/2 port, and communicate using the appropriate protocol. Converters also exist that connect PS/2 keyboards and mice (usually one of each) to a USB port. These devices present two HID endpoints to the system and use a microcontroller to perform bidirectional data translation between the two standards.
By design, it is difficult to insert a USB plug into its receptacle incorrectly. The USB specification states that the required USB icon must be embossed on the "topside" of the USB plug, which "...provides easy user recognition and facilitates alignment during the mating process." The specification also shows that the "recommended" "Manufacturer's logo" ("engraved" on the diagram but not specified in the text) is on the opposite side of the USB icon. The specification further states, "The USB Icon is also located adjacent to each receptacle. Receptacles should be oriented to allow the icon on the plug to be visible during the mating process." However, the specification does not consider the height of the device compared to the eye level height of the user, so the side of the cable that is "visible" when mated to a computer on a desk can depend on whether the user is standing or kneeling.
The standard connectors were deliberately intended to enforce the directed topology of a USB network: Type-A receptacles on host devices that supply power and Type-B receptacles on target devices that draw power. This prevents users from accidentally connecting two USB power supplies to each other, which could lead to short circuits and dangerously high currents, circuit failures, or even fire. USB does not support cyclic networks and the standard connectors from incompatible USB devices are themselves incompatible.
The standard connectors were designed to be robust. Because USB is hot-pluggable, the connectors would be used more frequently, and perhaps with less care, than other connectors. Many previous connector designs were fragile, specifying embedded component pins or other delicate parts that were vulnerable to bending or breaking. The electrical contacts in a USB connector are protected by an adjacent plastic tongue, and the entire connecting assembly is usually protected by an enclosing metal sheath.
The connector construction always ensures that the external sheath on the plug makes contact with its counterpart in the receptacle before any of the four connectors within make electrical contact. The external metallic sheath is typically connected to system ground, thus dissipating damaging static charges. This enclosure design also provides a degree of protection from electromagnetic interference to the USB signal while it travels through the mated connector pair (the only location when the otherwise twisted data pair travels in parallel). In addition, because of the required sizes of the power and common connections, they are made after the system ground but before the data connections. This type of staged make-break timing allows for electrically safe hot-swapping.
The newer micro-USB receptacles are designed for a minimum rated lifetime of 10,000 cycles of insertion and removal between the receptacle and plug, compared to 1,500 for the standard USB and 5,000 for the mini-USB receptacle. Features intended to accomplish include, a locking device was added and the leaf-spring was moved from the jack to the plug, so that the most-stressed part is on the cable side of the connection. This change was made so that the connector on the less expensive cable would bear the most wear instead of the more expensive micro-USB device. However the idea that these changes did in fact make the connector more durable in real world use has been widely disputed, with many contending that they are in fact, much less durable.
The USB standard specifies relatively loose tolerances for compliant USB connectors to minimize physical incompatibilities in connectors from different vendors. To address a weakness present in some other connector standards, the USB specification also defines limits to the size of a connecting device in the area around its plug. This was done to prevent a device from blocking adjacent ports due to the size of the cable strain relief mechanism (usually molding integral with the cable outer insulation) at the connector. Compliant devices must either fit within the size restrictions or support a compliant extension cable that does.
In general, USB cables have only plugs on their ends, while hosts and devices have only receptacles. Hosts almost universally have Type-A receptacles, while devices have one or another Type-B variety. Type-A plugs mate only with Type-A receptacles, and the same applies to their Type-B counterparts; they are deliberately physically incompatible. However, an extension to the USB standard specification called USB On-The-Go (OTG) allows a single port to act as either a host or a device, which is selectable by the end of the cable that plugs into the receptacle on the OTG-enabled unit. Even after the cable is hooked up and the units are communicating, the two units may "swap" ends under program control. This capability is meant for units such as PDAs in which the USB link might connect to a PC's host port as a device in one instance, yet connect as a host itself to a keyboard and mouse device in another instance.
Various connectors have been used for smaller devices such as digital cameras, smartphones, and tablet computers. These include the now-deprecated (i.e. de-certified but standardized) mini-A and mini-AB connectors; mini-B connectors are still supported, but are not OTG-compliant (On The Go, used in mobile devices). The mini-B USB connector was standard for transferring data to and from the early smartphones and PDAs. Both mini-A and mini-B plugs are approximately 3 by 7 mm; the mini-A connector and the mini-AB receptacle connector were deprecated on 23 May 2007.
The micro plug design is rated for at least 10,000 connect-disconnect cycles, which is more than the mini plug design. The micro connector is also designed to reduce the mechanical wear on the device; instead the easier-to-replace cable is designed to bear the mechanical wear of connection and disconnection. The Universal Serial Bus Micro-USB Cables and Connectors Specification details the mechanical characteristics of micro-A plugs, micro-AB receptacles (which accept both micro-A and micro-B plugs), and micro-B plugs and receptacles, along with a standard-A receptacle to micro-A plug adapter.
The cellular phone carrier group Open Mobile Terminal Platform (OMTP) in 2007 endorsed micro-USB as the standard connector for data and power on mobile devices In addition, on 22 October 2009 the International Telecommunication Union (ITU) has also announced that it had embraced micro-USB as the Universal Charging Solution its "energy-efficient one-charger-fits-all new mobile phone solution," and added: "Based on the Micro-USB interface, UCS chargers also include a 4-star or higher efficiency rating—up to three times more energy-efficient than an unrated charger."
The European Standardisation Bodies CEN, CENELEC and ETSI (independent of the OMTP/GSMA proposal) defined a common External Power Supply (EPS) for use with smartphones sold in the EU based on micro-USB. 14 of the world's largest mobile phone manufacturers signed the EU's common EPS Memorandum of Understanding (MoU). Apple, one of the original MoU signers, makes micro-USB adapters available – as permitted in the Common EPS MoU – for its iPhones equipped with Apple's proprietary 30-pin dock connector or (later) Lightning connector.
All current USB On-The-Go (OTG) devices are required to have one, and only one, USB connector: a micro-AB receptacle. Non-OTG compliant devices are not allowed to use the micro-AB receptacle, due to power supply shorting hazards on the VBUS line. The micro-AB receptacle is capable of accepting both micro-A and micro-B plugs, attached to any of the legal cables and adapters as defined in revision 1.01 of the micro-USB specification. Prior to the development of micro-USB, USB On-The-Go devices were required to use mini-AB receptacles to perform the equivalent job.

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