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Katō Kiyomasa was one of the most powerful and well-known lords of the Sengoku Era. He commanded most of Japan's major clans during the invasion of Korea (1592–1598). In a handbook he addressed to "all samurai, regardless of rank" he told his followers that a warrior's only duty in life was to "...grasp the long and the short swords and to die". He also ordered his followers to put forth great effort in studying the military classics, especially those related to loyalty and filial piety. He is best known for his quote: "If a man does not investigate into the matter of Bushido daily, it will be difficult for him to die a brave and manly death. Thus it is essential to engrave this business of the warrior into one's mind well."
Torii Mototada (1539–1600) was a feudal lord in the service of Tokugawa Ieyasu. On the eve of the battle of Sekigahara, he volunteered to remain behind in the doomed Fushimi Castle while his lord advanced to the east. Torii and Tokugawa both agreed that the castle was indefensible. In an act of loyalty to his lord, Torii chose to remain behind, pledging that he and his men would fight to the finish. As was custom, Torii vowed that he would not be taken alive. In a dramatic last stand, the garrison of 2,000 men held out against overwhelming odds for ten days against the massive army of Ishida Mitsunari's 40,000 warriors. In a moving last statement to his son Tadamasa, he wrote:
The rival of Takeda Shingen (1521–1573) was Uesugi Kenshin (1530–1578), a legendary Sengoku warlord well-versed in the Chinese military classics and who advocated the "way of the warrior as death". Japanese historian Daisetz Teitaro Suzuki describes Uesugi's beliefs as: "Those who are reluctant to give up their lives and embrace death are not true warriors.... Go to the battlefield firmly confident of victory, and you will come home with no wounds whatever. Engage in combat fully determined to die and you will be alive; wish to survive in the battle and you will surely meet death. When you leave the house determined not to see it again you will come home safely; when you have any thought of returning you will not return. You may not be in the wrong to think that the world is always subject to change, but the warrior must not entertain this way of thinking, for his fate is always determined."
Historian H. Paul Varley notes the description of Japan given by Jesuit leader St. Francis Xavier (1506–1552): "There is no nation in the world which fears death less." Xavier further describes the honour and manners of the people: "I fancy that there are no people in the world more punctilious about their honour than the Japanese, for they will not put up with a single insult or even a word spoken in anger." Xavier spent the years 1549–1551 converting Japanese to Christianity. He also observed: "The Japanese are much braver and more warlike than the people of China, Korea, Ternate and all of the other nations around the Philippines."
In December 1547, Francis was in Malacca (Malaysia) waiting to return to Goa (India) when he met a low-ranked samurai named Anjiro (possibly spelled "Yajiro"). Anjiro was not an intellectual, but he impressed Xavier because he took careful notes of everything he said in church. Xavier made the decision to go to Japan in part because this low-ranking samurai convinced him in Portuguese that the Japanese people were highly educated and eager to learn. They were hard workers and respectful of authority. In their laws and customs they were led by reason, and, should the Christian faith convince them of its truth, they would accept it en masse.
In his book "Ideals of the Samurai" translator William Scott Wilson states: "The warriors in the Heike Monogatari served as models for the educated warriors of later generations, and the ideals depicted by them were not assumed to be beyond reach. Rather, these ideals were vigorously pursued in the upper echelons of warrior society and recommended as the proper form of the Japanese man of arms. With the Heike Monogatari, the image of the Japanese warrior in literature came to its full maturity." Wilson then translates the writings of several warriors who mention the Heike Monogatari as an example for their men to follow.
As aristocrats for centuries, samurai developed their own cultures that influenced Japanese culture as a whole. The culture associated with the samurai such as the tea ceremony, monochrome ink painting, rock gardens and poetry were adopted by warrior patrons throughout the centuries 1200–1600. These practices were adapted from the Chinese arts. Zen monks introduced them to Japan and they were allowed to flourish due to the interest of powerful warrior elites. Musō Soseki (1275–1351) was a Zen monk who was advisor to both Emperor Go-Daigo and General Ashikaga Takauji (1304–58). Musō, as well as other monks, acted as political and cultural diplomat between Japan and China. Musō was particularly well known for his garden design. Another Ashikaga patron of the arts was Yoshimasa. His cultural advisor, the Zen monk Zeami, introduced tea ceremony to him. Previously, tea had been used primarily for Buddhist monks to stay awake during meditation.
For example, the full name of Oda Nobunaga would be "Oda Kazusanosuke Saburo Nobunaga" (織田上総介三郎信長), in which "Oda" is a clan or family name, "Kazusanosuke" is a title of vice-governor of Kazusa province, "Saburo" is a formal nickname (yobina), and "Nobunaga" is an adult name (nanori) given at genpuku, the coming of age ceremony. A man was addressed by his family name and his title, or by his yobina if he did not have a title. However, the nanori was a private name that could be used by only a very few, including the Emperor.
A samurai could take concubines but their backgrounds were checked by higher-ranked samurai. In many cases, taking a concubine was akin to a marriage. Kidnapping a concubine, although common in fiction, would have been shameful, if not criminal. If the concubine was a commoner, a messenger was sent with betrothal money or a note for exemption of tax to ask for her parents' acceptance. Even though the woman would not be a legal wife, a situation normally considered a demotion, many wealthy merchants believed that being the concubine of a samurai was superior to being the legal wife of a commoner. When a merchant's daughter married a samurai, her family's money erased the samurai's debts, and the samurai's social status improved the standing of the merchant family. If a samurai's commoner concubine gave birth to a son, the son could inherit his father's social status.
A samurai could divorce his wife for a variety of reasons with approval from a superior, but divorce was, while not entirely nonexistent, a rare event. A wife's failure to produce a son was cause for divorce, but adoption of a male heir was considered an acceptable alternative to divorce. A samurai could divorce for personal reasons, even if he simply did not like his wife, but this was generally avoided as it would embarrass the person who had arranged the marriage. A woman could also arrange a divorce, although it would generally take the form of the samurai divorcing her. After a divorce samurai had to return the betrothal money, which often prevented divorces.
Maintaining the household was the main duty of samurai women. This was especially crucial during early feudal Japan, when warrior husbands were often traveling abroad or engaged in clan battles. The wife, or okugatasama (meaning: one who remains in the home), was left to manage all household affairs, care for the children, and perhaps even defend the home forcibly. For this reason, many women of the samurai class were trained in wielding a polearm called a naginata or a special knife called the kaiken in an art called tantojutsu (lit. the skill of the knife), which they could use to protect their household, family, and honor if the need arose.
Traits valued in women of the samurai class were humility, obedience, self-control, strength, and loyalty. Ideally, a samurai wife would be skilled at managing property, keeping records, dealing with financial matters, educating the children (and perhaps servants, too), and caring for elderly parents or in-laws that may be living under her roof. Confucian law, which helped define personal relationships and the code of ethics of the warrior class required that a woman show subservience to her husband, filial piety to her parents, and care to the children. Too much love and affection was also said to indulge and spoil the youngsters. Thus, a woman was also to exercise discipline.
This does not mean that samurai women were always powerless. Powerful women both wisely and unwisely wielded power at various occasions. After Ashikaga Yoshimasa, 8th shogun of the Muromachi shogunate, lost interest in politics, his wife Hino Tomiko largely ruled in his place. Nene, wife of Toyotomi Hideyoshi, was known to overrule her husband's decisions at times and Yodo-dono, his concubine, became the de facto master of Osaka castle and the Toyotomi clan after Hideyoshi's death. Tachibana Ginchiyo was chosen to lead the Tachibana clan after her father's death. Chiyo, wife of Yamauchi Kazutoyo, has long been considered the ideal samurai wife. According to legend, she made her kimono out of a quilted patchwork of bits of old cloth and saved pennies to buy her husband a magnificent horse, on which he rode to many victories. The fact that Chiyo (though she is better known as "Wife of Yamauchi Kazutoyo") is held in such high esteem for her economic sense is illuminating in the light of the fact that she never produced an heir and the Yamauchi clan was succeeded by Kazutoyo's younger brother. The source of power for women may have been that samurai left their finances to their wives.
As the Tokugawa period progressed more value became placed on education, and the education of females beginning at a young age became important to families and society as a whole. Marriage criteria began to weigh intelligence and education as desirable attributes in a wife, right along with physical attractiveness. Though many of the texts written for women during the Tokugawa period only pertained to how a woman could become a successful wife and household manager, there were those that undertook the challenge of learning to read, and also tackled philosophical and literary classics. Nearly all women of the samurai class were literate by the end of the Tokugawa period.
The English sailor and adventurer William Adams (1564–1620) was the first Westerner to receive the dignity of samurai. The Shogun Tokugawa Ieyasu presented him with two swords representing the authority of a samurai, and decreed that William Adams the sailor was dead and that Anjin Miura (三浦按針), a samurai, was born. Adams also received the title of hatamoto (bannerman), a high-prestige position as a direct retainer in the Shogun's court. He was provided with generous revenues: "For the services that I have done and do daily, being employed in the Emperor's service, the Emperor has given me a living" (Letters). He was granted a fief in Hemi (逸見) within the boundaries of present-day Yokosuka City, "with eighty or ninety husbandmen, that be my slaves or servants" (Letters). His estate was valued at 250 koku. He finally wrote "God hath provided for me after my great misery", (Letters) by which he meant the disaster-ridden voyage that initially brought him to Japan.
Jan Joosten van Lodensteijn (1556?–1623?), a Dutch colleague of Adams' on their ill-fated voyage to Japan in the ship De Liefde, was also given similar privileges by Tokugawa Ieyasu. It appears Joosten became a samurai[citation needed] and was given a residence within Ieyasu's castle at Edo. Today, this area at the east exit of Tokyo Station is known as Yaesu (八重洲). Yaesu is a corruption of the Dutchman's Japanese name, Yayousu (耶楊子). Also in common with Adam's, Joostens was given a Red Seal Ship (朱印船) allowing him to trade between Japan and Indo-China. On a return journey from Batavia Joosten drowned after his ship ran aground.
In the same war, the Prussian Edward Schnell served the Aizu domain as a military instructor and procurer of weapons. He was granted the Japanese name Hiramatsu Buhei (平松武兵衛), which inverted the characters of the daimyo's name Matsudaira. Hiramatsu (Schnell) was given the right to wear swords, as well as a residence in the castle town of Wakamatsu, a Japanese wife, and retainers. In many contemporary references, he is portrayed wearing a Japanese kimono, overcoat, and swords, with Western riding trousers and boots.
As far back as the seventh century Japanese warriors wore a form of lamellar armor, this armor eventually evolved into the armor worn by the samurai. The first types of Japanese armors identified as samurai armor were known as yoroi. These early samurai armors were made from small individual scales known as kozane. The kozane were made from either iron or leather and were bound together into small strips, the strips were coated with lacquer to protect the kozane from water. A series of strips of kozane were then laced together with silk or leather lace and formed into a complete chest armor (dou or dō).
In the 1500s a new type of armor started to become popular due to the advent of firearms, new fighting tactics and the need for additional protection. The kozane dou made from individual scales was replaced by plate armor. This new armor, which used iron plated dou (dō), was referred to as Tosei-gusoku, or modern armor. Various other components of armor protected the samurai's body. The helmet kabuto was an important part of the samurai's armor. Samurai armor changed and developed as the methods of samurai warfare changed over the centuries. The known last use of samurai armor occurring in 1877 during the satsuma rebellion. As the last samurai rebellion was crushed, Japan modernized its defenses and turned to a national conscription army that used uniforms.
The term samurai originally meant "those who serve in close attendance to nobility", and was written with a Chinese character (or kanji) that had the same meaning. In Japanese, it was originally recorded in the Nara Period as a verb samorapu ("to watch, to keep watch, to observe, to be on the lookout for something; to serve, to attend"), which is believed to be derived from the frequentative form (morapu 守らふ) of the verb moru (守る, "to watch, to guard, to be on the lookout; to keep, to protect, to take care of, to be in charge of, to have as one's ward"). By the Heian period, this word had developed into the verb saburahu (さぶらふ, "to serve, to attend"), from which a deverbal noun saburahi (さぶらひ, "servant, attendant") was later derived, and this noun then yielded samurahi (さむらひ) in the Edo period. In Japanese literature, there is an early reference to samurai in the Kokinshū (古今集, early 10th century):
Bushi was the name given to the ancient Japanese soldiers from traditional warrior families. The bushi class was developed mainly in the north of Japan. They formed powerful clans, which in the 12th century were against the noble families who were grouping themselves to support the imperial family who lived in Kyoto. Samurai was a word used by the Kuge aristocratic class with warriors themselves preferring the word bushi. The term Bushidō, the "way of the warrior", is derived from this term and the mansion of a warrior was called bukeyashiki.
Most samurai were bound by a code of honor and were expected to set an example for those below them. A notable part of their code is seppuku (切腹, seppuku?) or hara kiri, which allowed a disgraced samurai to regain his honor by passing into death, where samurai were still beholden to social rules. Whilst there are many romanticized characterizations of samurai behavior such as the writing of Bushido (武士道, Bushidō?) in 1905, studies of Kobudo and traditional Budō indicate that the samurai were as practical on the battlefield as were any other warrior.
Despite the rampant romanticism of the 20th century, samurai could be disloyal and treacherous (e.g., Akechi Mitsuhide), cowardly, brave, or overly loyal (e.g., Kusunoki Masashige). Samurai were usually loyal to their immediate superiors, who in turn allied themselves with higher lords. These loyalties to the higher lords often shifted; for example, the high lords allied under Toyotomi Hideyoshi (豊臣秀吉) were served by loyal samurai, but the feudal lords under them could shift their support to Tokugawa, taking their samurai with them. There were, however, also notable instances where samurai would be disloyal to their lord or daimyo, when loyalty to the Emperor was seen to have supremacy.
Jidaigeki (literally historical drama) has always been a staple program on Japanese movies and television. The programs typically feature a samurai. Samurai films and westerns share a number of similarities and the two have influenced each other over the years. One of Japan’s most renowned directors, Akira Kurosawa, greatly influenced the samurai aspect in western film-making.[citation needed] George Lucas’ Star Wars series incorporated many aspects from the Seven Samurai film. One example is that in the Japanese film, seven samurai warriors are hired by local farmers to protect their land from being overrun by bandits; In George Lucas’ Star Wars: A New Hope, a similar situation arises. Kurosawa was inspired by the works of director John Ford and in turn Kurosawa's works have been remade into westerns such as The Seven Samurai into The Magnificent Seven and Yojimbo into A Fistful of Dollars. There is also a 26 episode anime adaptation (Samurai 7) of The Seven Samurai. Along with film, literature containing samurai influences are seen as well.
Most common are historical works where the protagonist is either a samurai or former samurai (or another rank or position) who possesses considerable martial skill. Eiji Yoshikawa is one of the most famous Japanese historical novelists. His retellings of popular works, including Taiko, Musashi and Heike Tale, are popular among readers for their epic narratives and rich realism in depicting samurai and warrior culture.[citation needed] The samurai have also appeared frequently in Japanese comics (manga) and animation (anime). Samurai-like characters are not just restricted to historical settings and a number of works set in the modern age, and even the future, include characters who live, train and fight like samurai. Examples are Samurai Champloo, Requiem from the Darkness, Muramasa: The Demon Blade, and Afro Samurai. Some of these works have made their way to the west, where it has been increasing in popularity with America.
Just in the last two decades,[when?] samurai have become more popular in America. “Hyperbolizing the samurai in such a way that they appear as a whole to be a loyal body of master warriors provides international interest in certain characters due to admirable traits” (Moscardi, N.D.). Through various medium, producers and writers have been capitalizing on the notion that Americans admire the samurai lifestyle. The animated series, Afro Samurai, became well-liked in American popular culture due to its blend of hack-and-slash animation and gritty urban music.
Created by Takashi Okazaki, Afro Samurai was initially a doujinshi, or manga series, which was then made into an animated series by Studio Gonzo. In 2007 the animated series debuted on American cable television on the Spike TV channel (Denison, 2010). The series was produced for American viewers which “embodies the trend... comparing hip-hop artists to samurai warriors, an image some rappers claim for themselves (Solomon, 2009). The storyline keeps in tone with the perception of a samurais finding vengeance against someone who has wronged him. Starring the voice of well known American actor Samuel L. Jackson, “Afro is the second-strongest fighter in a futuristic, yet, still feudal Japan and seeks revenge upon the gunman who killed his father” (King 2008). Due to its popularity, Afro Samurai was adopted into a full feature animated film and also became titles on gaming consoles such as the PlayStation 3 and Xbox. Not only has the samurai culture been adopted into animation and video games, it can also be seen in comic books.
American comic books have adopted the character type for stories of their own like the mutant-villain Silver Samurai of Marvel Comics. The design of this character preserves the samurai appearance; the villain is “Clad in traditional gleaming samurai armor and wielding an energy charged katana” (Buxton, 2013). Not only does the Silver Samurai make over 350 comic book appearances, the character is playable in several video games, such as Marvel Vs. Capcom 1 and 2. In 2013, the samurai villain was depicted in James Mangold’s film The Wolverine. Ten years before the Wolverine debuted, another film helped pave the way to ensure the samurai were made known to American cinema: A film released in 2003 titled The Last Samurai, starring Tom Cruise, is inspired by the samurai way of life. In the film, Cruise’s character finds himself deeply immersed in samurai culture. The character in the film, “Nathan Algren, is a fictional contrivance to make nineteenth-century Japanese history less foreign to American viewers”.(Ravina, 2010) After being captured by a group of samurai rebels, he becomes empathetic towards the cause they fight for. Taking place during the Meiji Period, Tom Cruise plays the role of US Army Captain Nathan Algren, who travels to Japan to train a rookie army in fighting off samurai rebel groups. Becoming a product of his environment, Algren joins the samurai clan in an attempt to rescue a captured samurai leader. “By the end of the film, he has clearly taken on many of the samurai traits, such as zen-like mastery of the sword, and a budding understanding of spirituality”. (Manion, 2006)
As the number of possible tests for even simple software components is practically infinite, all software testing uses some strategy to select tests that are feasible for the available time and resources. As a result, software testing typically (but not exclusively) attempts to execute a program or application with the intent of finding software bugs (errors or other defects). The job of testing is an iterative process as when one bug is fixed, it can illuminate other, deeper bugs, or can even create new ones.
Although testing can determine the correctness of software under the assumption of some specific hypotheses (see hierarchy of testing difficulty below), testing cannot identify all the defects within software. Instead, it furnishes a criticism or comparison that compares the state and behavior of the product against oracles—principles or mechanisms by which someone might recognize a problem. These oracles may include (but are not limited to) specifications, contracts, comparable products, past versions of the same product, inferences about intended or expected purpose, user or customer expectations, relevant standards, applicable laws, or other criteria.
A primary purpose of testing is to detect software failures so that defects may be discovered and corrected. Testing cannot establish that a product functions properly under all conditions but can only establish that it does not function properly under specific conditions. The scope of software testing often includes examination of code as well as execution of that code in various environments and conditions as well as examining the aspects of code: does it do what it is supposed to do and do what it needs to do. In the current culture of software development, a testing organization may be separate from the development team. There are various roles for testing team members. Information derived from software testing may be used to correct the process by which software is developed.
Software faults occur through the following processes. A programmer makes an error (mistake), which results in a defect (fault, bug) in the software source code. If this defect is executed, in certain situations the system will produce wrong results, causing a failure. Not all defects will necessarily result in failures. For example, defects in dead code will never result in failures. A defect can turn into a failure when the environment is changed. Examples of these changes in environment include the software being run on a new computer hardware platform, alterations in source data, or interacting with different software. A single defect may result in a wide range of failure symptoms.
A fundamental problem with software testing is that testing under all combinations of inputs and preconditions (initial state) is not feasible, even with a simple product.:17-18 This means that the number of defects in a software product can be very large and defects that occur infrequently are difficult to find in testing. More significantly, non-functional dimensions of quality (how it is supposed to be versus what it is supposed to do)—usability, scalability, performance, compatibility, reliability—can be highly subjective; something that constitutes sufficient value to one person may be intolerable to another.
Software developers can't test everything, but they can use combinatorial test design to identify the minimum number of tests needed to get the coverage they want. Combinatorial test design enables users to get greater test coverage with fewer tests. Whether they are looking for speed or test depth, they can use combinatorial test design methods to build structured variation into their test cases. Note that "coverage", as used here, is referring to combinatorial coverage, not requirements coverage.
It is commonly believed that the earlier a defect is found, the cheaper it is to fix it. The following table shows the cost of fixing the defect depending on the stage it was found. For example, if a problem in the requirements is found only post-release, then it would cost 10–100 times more to fix than if it had already been found by the requirements review. With the advent of modern continuous deployment practices and cloud-based services, the cost of re-deployment and maintenance may lessen over time.
There are many approaches available in software testing. Reviews, walkthroughs, or inspections are referred to as static testing, whereas actually executing programmed code with a given set of test cases is referred to as dynamic testing. Static testing is often implicit, as proofreading, plus when programming tools/text editors check source code structure or compilers (pre-compilers) check syntax and data flow as static program analysis. Dynamic testing takes place when the program itself is run. Dynamic testing may begin before the program is 100% complete in order to test particular sections of code and are applied to discrete functions or modules. Typical techniques for this are either using stubs/drivers or execution from a debugger environment.
White-box testing (also known as clear box testing, glass box testing, transparent box testing and structural testing, by seeing the source code) tests internal structures or workings of a program, as opposed to the functionality exposed to the end-user. In white-box testing an internal perspective of the system, as well as programming skills, are used to design test cases. The tester chooses inputs to exercise paths through the code and determine the appropriate outputs. This is analogous to testing nodes in a circuit, e.g. in-circuit testing (ICT).
Black-box testing treats the software as a "black box", examining functionality without any knowledge of internal implementation, without seeing the source code. The testers are only aware of what the software is supposed to do, not how it does it. Black-box testing methods include: equivalence partitioning, boundary value analysis, all-pairs testing, state transition tables, decision table testing, fuzz testing, model-based testing, use case testing, exploratory testing and specification-based testing.
Specification-based testing aims to test the functionality of software according to the applicable requirements. This level of testing usually requires thorough test cases to be provided to the tester, who then can simply verify that for a given input, the output value (or behavior), either "is" or "is not" the same as the expected value specified in the test case. Test cases are built around specifications and requirements, i.e., what the application is supposed to do. It uses external descriptions of the software, including specifications, requirements, and designs to derive test cases. These tests can be functional or non-functional, though usually functional.
One advantage of the black box technique is that no programming knowledge is required. Whatever biases the programmers may have had, the tester likely has a different set and may emphasize different areas of functionality. On the other hand, black-box testing has been said to be "like a walk in a dark labyrinth without a flashlight." Because they do not examine the source code, there are situations when a tester writes many test cases to check something that could have been tested by only one test case, or leaves some parts of the program untested.
Grey-box testing (American spelling: gray-box testing) involves having knowledge of internal data structures and algorithms for purposes of designing tests, while executing those tests at the user, or black-box level. The tester is not required to have full access to the software's source code.[not in citation given] Manipulating input data and formatting output do not qualify as grey-box, because the input and output are clearly outside of the "black box" that we are calling the system under test. This distinction is particularly important when conducting integration testing between two modules of code written by two different developers, where only the interfaces are exposed for test.
By knowing the underlying concepts of how the software works, the tester makes better-informed testing choices while testing the software from outside. Typically, a grey-box tester will be permitted to set up an isolated testing environment with activities such as seeding a database. The tester can observe the state of the product being tested after performing certain actions such as executing SQL statements against the database and then executing queries to ensure that the expected changes have been reflected. Grey-box testing implements intelligent test scenarios, based on limited information. This will particularly apply to data type handling, exception handling, and so on.
There are generally four recognized levels of tests: unit testing, integration testing, component interface testing, and system testing. Tests are frequently grouped by where they are added in the software development process, or by the level of specificity of the test. The main levels during the development process as defined by the SWEBOK guide are unit-, integration-, and system testing that are distinguished by the test target without implying a specific process model. Other test levels are classified by the testing objective.
Unit testing is a software development process that involves synchronized application of a broad spectrum of defect prevention and detection strategies in order to reduce software development risks, time, and costs. It is performed by the software developer or engineer during the construction phase of the software development lifecycle. Rather than replace traditional QA focuses, it augments it. Unit testing aims to eliminate construction errors before code is promoted to QA; this strategy is intended to increase the quality of the resulting software as well as the efficiency of the overall development and QA process.
The practice of component interface testing can be used to check the handling of data passed between various units, or subsystem components, beyond full integration testing between those units. The data being passed can be considered as "message packets" and the range or data types can be checked, for data generated from one unit, and tested for validity before being passed into another unit. One option for interface testing is to keep a separate log file of data items being passed, often with a timestamp logged to allow analysis of thousands of cases of data passed between units for days or weeks. Tests can include checking the handling of some extreme data values while other interface variables are passed as normal values. Unusual data values in an interface can help explain unexpected performance in the next unit. Component interface testing is a variation of black-box testing, with the focus on the data values beyond just the related actions of a subsystem component.
Operational Acceptance is used to conduct operational readiness (pre-release) of a product, service or system as part of a quality management system. OAT is a common type of non-functional software testing, used mainly in software development and software maintenance projects. This type of testing focuses on the operational readiness of the system to be supported, and/or to become part of the production environment. Hence, it is also known as operational readiness testing (ORT) or Operations readiness and assurance (OR&A) testing. Functional testing within OAT is limited to those tests which are required to verify the non-functional aspects of the system.
A common cause of software failure (real or perceived) is a lack of its compatibility with other application software, operating systems (or operating system versions, old or new), or target environments that differ greatly from the original (such as a terminal or GUI application intended to be run on the desktop now being required to become a web application, which must render in a web browser). For example, in the case of a lack of backward compatibility, this can occur because the programmers develop and test software only on the latest version of the target environment, which not all users may be running. This results in the unintended consequence that the latest work may not function on earlier versions of the target environment, or on older hardware that earlier versions of the target environment was capable of using. Sometimes such issues can be fixed by proactively abstracting operating system functionality into a separate program module or library.
Regression testing focuses on finding defects after a major code change has occurred. Specifically, it seeks to uncover software regressions, as degraded or lost features, including old bugs that have come back. Such regressions occur whenever software functionality that was previously working correctly, stops working as intended. Typically, regressions occur as an unintended consequence of program changes, when the newly developed part of the software collides with the previously existing code. Common methods of regression testing include re-running previous sets of test-cases and checking whether previously fixed faults have re-emerged. The depth of testing depends on the phase in the release process and the risk of the added features. They can either be complete, for changes added late in the release or deemed to be risky, or be very shallow, consisting of positive tests on each feature, if the changes are early in the release or deemed to be of low risk. Regression testing is typically the largest test effort in commercial software development, due to checking numerous details in prior software features, and even new software can be developed while using some old test-cases to test parts of the new design to ensure prior functionality is still supported.
Beta testing comes after alpha testing and can be considered a form of external user acceptance testing. Versions of the software, known as beta versions, are released to a limited audience outside of the programming team known as beta testers. The software is released to groups of people so that further testing can ensure the product has few faults or bugs. Beta versions can be made available to the open public to increase the feedback field to a maximal number of future users and to deliver value earlier, for an extended or even indefinite period of time (perpetual beta).[citation needed]
Destructive testing attempts to cause the software or a sub-system to fail. It verifies that the software functions properly even when it receives invalid or unexpected inputs, thereby establishing the robustness of input validation and error-management routines.[citation needed] Software fault injection, in the form of fuzzing, is an example of failure testing. Various commercial non-functional testing tools are linked from the software fault injection page; there are also numerous open-source and free software tools available that perform destructive testing.
Load testing is primarily concerned with testing that the system can continue to operate under a specific load, whether that be large quantities of data or a large number of users. This is generally referred to as software scalability. The related load testing activity of when performed as a non-functional activity is often referred to as endurance testing. Volume testing is a way to test software functions even when certain components (for example a file or database) increase radically in size. Stress testing is a way to test reliability under unexpected or rare workloads. Stability testing (often referred to as load or endurance testing) checks to see if the software can continuously function well in or above an acceptable period.
Development Testing is a software development process that involves synchronized application of a broad spectrum of defect prevention and detection strategies in order to reduce software development risks, time, and costs. It is performed by the software developer or engineer during the construction phase of the software development lifecycle. Rather than replace traditional QA focuses, it augments it. Development Testing aims to eliminate construction errors before code is promoted to QA; this strategy is intended to increase the quality of the resulting software as well as the efficiency of the overall development and QA process.
In contrast, some emerging software disciplines such as extreme programming and the agile software development movement, adhere to a "test-driven software development" model. In this process, unit tests are written first, by the software engineers (often with pair programming in the extreme programming methodology). Of course these tests fail initially; as they are expected to. Then as code is written it passes incrementally larger portions of the test suites. The test suites are continuously updated as new failure conditions and corner cases are discovered, and they are integrated with any regression tests that are developed. Unit tests are maintained along with the rest of the software source code and generally integrated into the build process (with inherently interactive tests being relegated to a partially manual build acceptance process). The ultimate goal of this test process is to achieve continuous integration where software updates can be published to the public frequently.
Bottom Up Testing is an approach to integrated testing where the lowest level components (modules, procedures, and functions) are tested first, then integrated and used to facilitate the testing of higher level components. After the integration testing of lower level integrated modules, the next level of modules will be formed and can be used for integration testing. The process is repeated until the components at the top of the hierarchy are tested. This approach is helpful only when all or most of the modules of the same development level are ready.[citation needed] This method also helps to determine the levels of software developed and makes it easier to report testing progress in the form of a percentage.[citation needed]
It has been proved that each class is strictly included into the next. For instance, testing when we assume that the behavior of the implementation under test can be denoted by a deterministic finite-state machine for some known finite sets of inputs and outputs and with some known number of states belongs to Class I (and all subsequent classes). However, if the number of states is not known, then it only belongs to all classes from Class II on. If the implementation under test must be a deterministic finite-state machine failing the specification for a single trace (and its continuations), and its number of states is unknown, then it only belongs to classes from Class III on. Testing temporal machines where transitions are triggered if inputs are produced within some real-bounded interval only belongs to classes from Class IV on, whereas testing many non-deterministic systems only belongs to Class V (but not all, and some even belong to Class I). The inclusion into Class I does not require the simplicity of the assumed computation model, as some testing cases involving implementations written in any programming language, and testing implementations defined as machines depending on continuous magnitudes, have been proved to be in Class I. Other elaborated cases, such as the testing framework by Matthew Hennessy under must semantics, and temporal machines with rational timeouts, belong to Class II.
Several certification programs exist to support the professional aspirations of software testers and quality assurance specialists. No certification now offered actually requires the applicant to show their ability to test software. No certification is based on a widely accepted body of knowledge. This has led some to declare that the testing field is not ready for certification. Certification itself cannot measure an individual's productivity, their skill, or practical knowledge, and cannot guarantee their competence, or professionalism as a tester.
Software testing is a part of the software quality assurance (SQA) process.:347 In SQA, software process specialists and auditors are concerned for the software development process rather than just the artifacts such as documentation, code and systems. They examine and change the software engineering process itself to reduce the number of faults that end up in the delivered software: the so-called "defect rate". What constitutes an "acceptable defect rate" depends on the nature of the software; A flight simulator video game would have much higher defect tolerance than software for an actual airplane. Although there are close links with SQA, testing departments often exist independently, and there may be no SQA function in some companies.[citation needed]
Many applications of silicate glasses derive from their optical transparency, which gives rise to one of silicate glasses' primary uses as window panes. Glass will transmit, reflect and refract light; these qualities can be enhanced by cutting and polishing to make optical lenses, prisms, fine glassware, and optical fibers for high speed data transmission by light. Glass can be colored by adding metallic salts, and can also be painted and printed with vitreous enamels. These qualities have led to the extensive use of glass in the manufacture of art objects and in particular, stained glass windows. Although brittle, silicate glass is extremely durable, and many examples of glass fragments exist from early glass-making cultures. Because glass can be formed or molded into any shape, and also because it is a sterile product, it has been traditionally used for vessels: bowls, vases, bottles, jars and drinking glasses. In its most solid forms it has also been used for paperweights, marbles, and beads. When extruded as glass fiber and matted as glass wool in a way to trap air, it becomes a thermal insulating material, and when these glass fibers are embedded into an organic polymer plastic, they are a key structural reinforcement part of the composite material fiberglass. Some objects historically were so commonly made of silicate glass that they are simply called by the name of the material, such as drinking glasses and reading glasses.
Most common glass contains other ingredients to change its properties. Lead glass or flint glass is more 'brilliant' because the increased refractive index causes noticeably more specular reflection and increased optical dispersion. Adding barium also increases the refractive index. Thorium oxide gives glass a high refractive index and low dispersion and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern eyeglasses.[citation needed] Iron can be incorporated into glass to absorb infrared energy, for example in heat absorbing filters for movie projectors, while cerium(IV) oxide can be used for glass that absorbs UV wavelengths.
Fused quartz is a glass made from chemically-pure SiO2 (silica). It has excellent thermal shock characteristics, being able to survive immersion in water while red hot. However, its high melting-temperature (1723 °C) and viscosity make it difficult to work with. Normally, other substances are added to simplify processing. One is sodium carbonate (Na2CO3, "soda"), which lowers the glass transition temperature. The soda makes the glass water-soluble, which is usually undesirable, so lime (calcium oxide [CaO], generally obtained from limestone), some magnesium oxide (MgO) and aluminium oxide (Al2O3) are added to provide for a better chemical durability. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass. Soda-lime glasses account for about 90% of manufactured glass.
Following the glass batch preparation and mixing, the raw materials are transported to the furnace. Soda-lime glass for mass production is melted in gas fired units. Smaller scale furnaces for specialty glasses include electric melters, pot furnaces, and day tanks. After melting, homogenization and refining (removal of bubbles), the glass is formed. Flat glass for windows and similar applications is formed by the float glass process, developed between 1953 and 1957 by Sir Alastair Pilkington and Kenneth Bickerstaff of the UK's Pilkington Brothers, who created a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity. The top surface of the glass is subjected to nitrogen under pressure to obtain a polished finish. Container glass for common bottles and jars is formed by blowing and pressing methods. This glass is often slightly modified chemically (with more alumina and calcium oxide) for greater water resistance. Further glass forming techniques are summarized in the table Glass forming techniques.
Glass has the ability to refract, reflect, and transmit light following geometrical optics, without scattering it. It is used in the manufacture of lenses and windows. Common glass has a refraction index around 1.5. This may be modified by adding low-density materials such as boron, which lowers the index of refraction (see crown glass), or increased (to as much as 1.8) with high-density materials such as (classically) lead oxide (see flint glass and lead glass), or in modern uses, less toxic oxides of zirconium, titanium, or barium. These high-index glasses (inaccurately known as "crystal" when used in glass vessels) cause more chromatic dispersion of light, and are prized for their diamond-like optical properties.
The most familiar, and historically the oldest, types of glass are "silicate glasses" based on the chemical compound silica (silicon dioxide, or quartz), the primary constituent of sand. The term glass, in popular usage, is often used to refer only to this type of material, which is familiar from use as window glass and in glass bottles. Of the many silica-based glasses that exist, ordinary glazing and container glass is formed from a specific type called soda-lime glass, composed of approximately 75% silicon dioxide (SiO2), sodium oxide (Na2O) from sodium carbonate (Na2CO3), calcium oxide, also called lime (CaO), and several minor additives. A very clear and durable quartz glass can be made from pure silica, but the high melting point and very narrow glass transition of quartz make glassblowing and hot working difficult. In glasses like soda lime, the compounds added to quartz are used to lower the melting temperature and improve workability, at a cost in the toughness, thermal stability, and optical transmittance.
Glass is in widespread use largely due to the production of glass compositions that are transparent to visible light. In contrast, polycrystalline materials do not generally transmit visible light. The individual crystallites may be transparent, but their facets (grain boundaries) reflect or scatter light resulting in diffuse reflection. Glass does not contain the internal subdivisions associated with grain boundaries in polycrystals and hence does not scatter light in the same manner as a polycrystalline material. The surface of a glass is often smooth since during glass formation the molecules of the supercooled liquid are not forced to dispose in rigid crystal geometries and can follow surface tension, which imposes a microscopically smooth surface. These properties, which give glass its clearness, can be retained even if glass is partially light-absorbing—i.e., colored.
Naturally occurring glass, especially the volcanic glass obsidian, has been used by many Stone Age societies across the globe for the production of sharp cutting tools and, due to its limited source areas, was extensively traded. But in general, archaeological evidence suggests that the first true glass was made in coastal north Syria, Mesopotamia or ancient Egypt. The earliest known glass objects, of the mid third millennium BCE, were beads, perhaps initially created as accidental by-products of metal-working (slags) or during the production of faience, a pre-glass vitreous material made by a process similar to glazing.
Color in glass may be obtained by addition of electrically charged ions (or color centers) that are homogeneously distributed, and by precipitation of finely dispersed particles (such as in photochromic glasses). Ordinary soda-lime glass appears colorless to the naked eye when it is thin, although iron(II) oxide (FeO) impurities of up to 0.1 wt% produce a green tint, which can be viewed in thick pieces or with the aid of scientific instruments. Further FeO and Cr2O3 additions may be used for the production of green bottles. Sulfur, together with carbon and iron salts, is used to form iron polysulfides and produce amber glass ranging from yellowish to almost black. A glass melt can also acquire an amber color from a reducing combustion atmosphere. Manganese dioxide can be added in small amounts to remove the green tint given by iron(II) oxide. When used in art glass or studio glass is colored using closely guarded recipes that involve specific combinations of metal oxides, melting temperatures and 'cook' times. Most colored glass used in the art market is manufactured in volume by vendors who serve this market although there are some glassmakers with the ability to make their own color from raw materials.
Glass remained a luxury material, and the disasters that overtook Late Bronze Age civilizations seem to have brought glass-making to a halt. Indigenous development of glass technology in South Asia may have begun in 1730 BCE. In ancient China, though, glassmaking seems to have a late start, compared to ceramics and metal work. The term glass developed in the late Roman Empire. It was in the Roman glassmaking center at Trier, now in modern Germany, that the late-Latin term glesum originated, probably from a Germanic word for a transparent, lustrous substance. Glass objects have been recovered across the Roman empire in domestic, industrial and funerary contexts.[citation needed]
Glass was used extensively during the Middle Ages. Anglo-Saxon glass has been found across England during archaeological excavations of both settlement and cemetery sites. Glass in the Anglo-Saxon period was used in the manufacture of a range of objects including vessels, beads, windows and was also used in jewelry. From the 10th-century onwards, glass was employed in stained glass windows of churches and cathedrals, with famous examples at Chartres Cathedral and the Basilica of Saint Denis. By the 14th-century, architects were designing buildings with walls of stained glass such as Sainte-Chapelle, Paris, (1203–1248) and the East end of Gloucester Cathedral. Stained glass had a major revival with Gothic Revival architecture in the 19th-century. With the Renaissance, and a change in architectural style, the use of large stained glass windows became less prevalent. The use of domestic stained glass increased until most substantial houses had glass windows. These were initially small panes leaded together, but with the changes in technology, glass could be manufactured relatively cheaply in increasingly larger sheets. This led to larger window panes, and, in the 20th-century, to much larger windows in ordinary domestic and commercial buildings.
In the 20th century, new types of glass such as laminated glass, reinforced glass and glass bricks have increased the use of glass as a building material and resulted in new applications of glass. Multi-storey buildings are frequently constructed with curtain walls made almost entirely of glass. Similarly, laminated glass has been widely applied to vehicles for windscreens. While glass containers have always been used for storage and are valued for their hygienic properties, glass has been utilized increasingly in industry. Optical glass for spectacles has been used since the late Middle Ages. The production of lenses has become increasingly proficient, aiding astronomers as well as having other application in medicine and science. Glass is also employed as the aperture cover in many solar energy systems.
From the 19th century, there was a revival in many ancient glass-making techniques including cameo glass, achieved for the first time since the Roman Empire and initially mostly used for pieces in a neo-classical style. The Art Nouveau movement made great use of glass, with René Lalique, Émile Gallé, and Daum of Nancy producing colored vases and similar pieces, often in cameo glass, and also using luster techniques. Louis Comfort Tiffany in America specialized in stained glass, both secular and religious, and his famous lamps. The early 20th-century saw the large-scale factory production of glass art by firms such as Waterford and Lalique. From about 1960 onwards there have been an increasing number of small studios hand-producing glass artworks, and glass artists began to class themselves as in effect sculptors working in glass, and their works as part fine arts.
Addition of lead(II) oxide lowers melting point, lowers viscosity of the melt, and increases refractive index. Lead oxide also facilitates solubility of other metal oxides and is used in colored glasses. The viscosity decrease of lead glass melt is very significant (roughly 100 times in comparison with soda glasses); this allows easier removal of bubbles and working at lower temperatures, hence its frequent use as an additive in vitreous enamels and glass solders. The high ionic radius of the Pb2+ ion renders it highly immobile in the matrix and hinders the movement of other ions; lead glasses therefore have high electrical resistance, about two orders of magnitude higher than soda-lime glass (108.5 vs 106.5 Ohm·cm, DC at 250 °C). For more details, see lead glass.
There are three classes of components for oxide glasses: network formers, intermediates, and modifiers. The network formers (silicon, boron, germanium) form a highly cross-linked network of chemical bonds. The intermediates (titanium, aluminium, zirconium, beryllium, magnesium, zinc) can act as both network formers and modifiers, according to the glass composition. The modifiers (calcium, lead, lithium, sodium, potassium) alter the network structure; they are usually present as ions, compensated by nearby non-bridging oxygen atoms, bound by one covalent bond to the glass network and holding one negative charge to compensate for the positive ion nearby. Some elements can play multiple roles; e.g. lead can act both as a network former (Pb4+ replacing Si4+), or as a modifier.
The alkali metal ions are small and mobile; their presence in glass allows a degree of electrical conductivity, especially in molten state or at high temperature. Their mobility decreases the chemical resistance of the glass, allowing leaching by water and facilitating corrosion. Alkaline earth ions, with their two positive charges and requirement for two non-bridging oxygen ions to compensate for their charge, are much less mobile themselves and also hinder diffusion of other ions, especially the alkalis. The most common commercial glasses contain both alkali and alkaline earth ions (usually sodium and calcium), for easier processing and satisfying corrosion resistance. Corrosion resistance of glass can be achieved by dealkalization, removal of the alkali ions from the glass surface by reaction with e.g. sulfur or fluorine compounds. Presence of alkaline metal ions has also detrimental effect to the loss tangent of the glass, and to its electrical resistance; glasses for electronics (sealing, vacuum tubes, lamps...) have to take this in account.
New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure chemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as alkali or alkaline earth metal oxides and hydroxides, or boron oxide), or that the impurities are quantified (loss on ignition). Evaporation losses during glass melting should be considered during the selection of the raw materials, e.g., sodium selenite may be preferred over easily evaporating SeO2. Also, more readily reacting raw materials may be preferred over relatively inert ones, such as Al(OH)3 over Al2O3. Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glass homogeneity is achieved by homogenizing the raw materials mixture (glass batch), by stirring the melt, and by crushing and re-melting the first melt. The obtained glass is usually annealed to prevent breakage during processing.
In the past, small batches of amorphous metals with high surface area configurations (ribbons, wires, films, etc.) have been produced through the implementation of extremely rapid rates of cooling. This was initially termed "splat cooling" by doctoral student W. Klement at Caltech, who showed that cooling rates on the order of millions of degrees per second is sufficient to impede the formation of crystals, and the metallic atoms become "locked into" a glassy state. Amorphous metal wires have been produced by sputtering molten metal onto a spinning metal disk. More recently a number of alloys have been produced in layers with thickness exceeding 1 millimeter. These are known as bulk metallic glasses (BMG). Liquidmetal Technologies sell a number of zirconium-based BMGs. Batches of amorphous steel have also been produced that demonstrate mechanical properties far exceeding those found in conventional steel alloys.
In 2004, NIST researchers presented evidence that an isotropic non-crystalline metallic phase (dubbed "q-glass") could be grown from the melt. This phase is the first phase, or "primary phase," to form in the Al-Fe-Si system during rapid cooling. Interestingly, experimental evidence indicates that this phase forms by a first-order transition. Transmission electron microscopy (TEM) images show that the q-glass nucleates from the melt as discrete particles, which grow spherically with a uniform growth rate in all directions. The diffraction pattern shows it to be an isotropic glassy phase. Yet there is a nucleation barrier, which implies an interfacial discontinuity (or internal surface) between the glass and the melt.
Glass-ceramic materials share many properties with both non-crystalline glass and crystalline ceramics. They are formed as a glass, and then partially crystallized by heat treatment. For example, the microstructure of whiteware ceramics frequently contains both amorphous and crystalline phases. Crystalline grains are often embedded within a non-crystalline intergranular phase of grain boundaries. When applied to whiteware ceramics, vitreous means the material has an extremely low permeability to liquids, often but not always water, when determined by a specified test regime.
The term mainly refers to a mix of lithium and aluminosilicates that yields an array of materials with interesting thermomechanical properties. The most commercially important of these have the distinction of being impervious to thermal shock. Thus, glass-ceramics have become extremely useful for countertop cooking. The negative thermal expansion coefficient (CTE) of the crystalline ceramic phase can be balanced with the positive CTE of the glassy phase. At a certain point (~70% crystalline) the glass-ceramic has a net CTE near zero. This type of glass-ceramic exhibits excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000 °C.
Mass production of glass window panes in the early twentieth century caused a similar effect. In glass factories, molten glass was poured onto a large cooling table and allowed to spread. The resulting glass is thicker at the location of the pour, located at the center of the large sheet. These sheets were cut into smaller window panes with nonuniform thickness, typically with the location of the pour centered in one of the panes (known as "bull's-eyes") for decorative effect. Modern glass intended for windows is produced as float glass and is very uniform in thickness.
The observation that old windows are sometimes found to be thicker at the bottom than at the top is often offered as supporting evidence for the view that glass flows over a timescale of centuries, the assumption being that the glass has exhibited the liquid property of flowing from one shape to another. This assumption is incorrect, as once solidified, glass stops flowing. The reason for the observation is that in the past, when panes of glass were commonly made by glassblowers, the technique used was to spin molten glass so as to create a round, mostly flat and even plate (the crown glass process, described above). This plate was then cut to fit a window. The pieces were not absolutely flat; the edges of the disk became a different thickness as the glass spun. When installed in a window frame, the glass would be placed with the thicker side down both for the sake of stability and to prevent water accumulating in the lead cames at the bottom of the window. Occasionally such glass has been found installed with the thicker side at the top, left or right.
In physics, the standard definition of a glass (or vitreous solid) is a solid formed by rapid melt quenching. The term glass is often used to describe any amorphous solid that exhibits a glass transition temperature Tg. If the cooling is sufficiently rapid (relative to the characteristic crystallization time) then crystallization is prevented and instead the disordered atomic configuration of the supercooled liquid is frozen into the solid state at Tg. The tendency for a material to form a glass while quenched is called glass-forming ability. This ability can be predicted by the rigidity theory. Generally, the structure of a glass exists in a metastable state with respect to its crystalline form, although in certain circumstances, for example in atactic polymers, there is no crystalline analogue of the amorphous phase.
Some people consider glass to be a liquid due to its lack of a first-order phase transition where certain thermodynamic variables such as volume, entropy and enthalpy are discontinuous through the glass transition range. The glass transition may be described as analogous to a second-order phase transition where the intensive thermodynamic variables such as the thermal expansivity and heat capacity are discontinuous. Nonetheless, the equilibrium theory of phase transformations does not entirely hold for glass, and hence the glass transition cannot be classed as one of the classical equilibrium phase transformations in solids.
Although the atomic structure of glass shares characteristics of the structure in a supercooled liquid, glass tends to behave as a solid below its glass transition temperature. A supercooled liquid behaves as a liquid, but it is below the freezing point of the material, and in some cases will crystallize almost instantly if a crystal is added as a core. The change in heat capacity at a glass transition and a melting transition of comparable materials are typically of the same order of magnitude, indicating that the change in active degrees of freedom is comparable as well. Both in a glass and in a crystal it is mostly only the vibrational degrees of freedom that remain active, whereas rotational and translational motion is arrested. This helps to explain why both crystalline and non-crystalline solids exhibit rigidity on most experimental time scales.
Public policy and political leadership helps to "level the playing field" and drive the wider acceptance of renewable energy technologies. Countries such as Germany, Denmark, and Spain have led the way in implementing innovative policies which has driven most of the growth over the past decade. As of 2014, Germany has a commitment to the "Energiewende" transition to a sustainable energy economy, and Denmark has a commitment to 100% renewable energy by 2050. There are now 144 countries with renewable energy policy targets.
Total investment in renewable energy (including small hydro-electric projects) was $244 billion in 2012, down 12% from 2011 mainly due to dramatically lower solar prices and weakened US and EU markets. As a share of total investment in power plants, wind and solar PV grew from 14% in 2000 to over 60% in 2012. The top countries for investment in recent years were China, Germany, Spain, the United States, Italy, and Brazil. Renewable energy companies include BrightSource Energy, First Solar, Gamesa, GE Energy, Goldwind, Sinovel, Trina Solar, Vestas and Yingli.
EU member countries have shown support for ambitious renewable energy goals. In 2010, Eurobarometer polled the twenty-seven EU member states about the target "to increase the share of renewable energy in the EU by 20 percent by 2020". Most people in all twenty-seven countries either approved of the target or called for it to go further. Across the EU, 57 percent thought the proposed goal was "about right" and 16 percent thought it was "too modest." In comparison, 19 percent said it was "too ambitious".
By the end of 2011, total renewable power capacity worldwide exceeded 1,360 GW, up 8%. Renewables producing electricity accounted for almost half of the 208 GW of capacity added globally during 2011. Wind and solar photovoltaics (PV) accounted for almost 40% and 30% . Based on REN21's 2014 report, renewables contributed 19 percent to our energy consumption and 22 percent to our electricity generation in 2012 and 2013, respectively. This energy consumption is divided as 9% coming from traditional biomass, 4.2% as heat energy (non-biomass), 3.8% hydro electricity and 2% electricity from wind, solar, geothermal, and biomass.
During the five-years from the end of 2004 through 2009, worldwide renewable energy capacity grew at rates of 10–60 percent annually for many technologies. In 2011, UN under-secretary general Achim Steiner said: "The continuing growth in this core segment of the green economy is not happening by chance. The combination of government target-setting, policy support and stimulus funds is underpinning the renewable industry's rise and bringing the much needed transformation of our global energy system within reach." He added: "Renewable energies are expanding both in terms of investment, projects and geographical spread. In doing so, they are making an increasing contribution to combating climate change, countering energy poverty and energy insecurity".
According to a 2011 projection by the International Energy Agency, solar power plants may produce most of the world's electricity within 50 years, significantly reducing the emissions of greenhouse gases that harm the environment. The IEA has said: "Photovoltaic and solar-thermal plants may meet most of the world's demand for electricity by 2060 – and half of all energy needs – with wind, hydropower and biomass plants supplying much of the remaining generation". "Photovoltaic and concentrated solar power together can become the major source of electricity".
In 2013, China led the world in renewable energy production, with a total capacity of 378 GW, mainly from hydroelectric and wind power. As of 2014, China leads the world in the production and use of wind power, solar photovoltaic power and smart grid technologies, generating almost as much water, wind and solar energy as all of France and Germany's power plants combined. China's renewable energy sector is growing faster than its fossil fuels and nuclear power capacity. Since 2005, production of solar cells in China has expanded 100-fold. As Chinese renewable manufacturing has grown, the costs of renewable energy technologies have dropped. Innovation has helped, but the main driver of reduced costs has been market expansion.
Renewable energy technologies are getting cheaper, through technological change and through the benefits of mass production and market competition. A 2011 IEA report said: "A portfolio of renewable energy technologies is becoming cost-competitive in an increasingly broad range of circumstances, in some cases providing investment opportunities without the need for specific economic support," and added that "cost reductions in critical technologies, such as wind and solar, are set to continue." As of 2011[update], there have been substantial reductions in the cost of solar and wind technologies:
Renewable energy is also the most economic solution for new grid-connected capacity in areas with good resources. As the cost of renewable power falls, the scope of economically viable applications increases. Renewable technologies are now often the most economic solution for new generating capacity. Where "oil-fired generation is the predominant power generation source (e.g. on islands, off-grid and in some countries) a lower-cost renewable solution almost always exists today". As of 2012, renewable power generation technologies accounted for around half of all new power generation capacity additions globally. In 2011, additions included 41 gigawatt (GW) of new wind power capacity, 30 GW of PV, 25 GW of hydro-electricity, 6 GW of biomass, 0.5 GW of CSP, and 0.1 GW of geothermal power.
Biomass for heat and power is a fully mature technology which offers a ready disposal mechanism for municipal, agricultural, and industrial organic wastes. However, the industry has remained relatively stagnant over the decade to 2007, even though demand for biomass (mostly wood) continues to grow in many developing countries. One of the problems of biomass is that material directly combusted in cook stoves produces pollutants, leading to severe health and environmental consequences, although improved cook stove programmes are alleviating some of these effects. First-generation biomass technologies can be economically competitive, but may still require deployment support to overcome public acceptance and small-scale issues.
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy, accounting for 16 percent of global electricity generation – 3,427 terawatt-hours of electricity production in 2010, and is expected to increase about 3.1% each year for the next 25 years. Hydroelectric plants have the advantage of being long-lived and many existing plants have operated for more than 100 years.
Hydropower is produced in 150 countries, with the Asia-Pacific region generating 32 percent of global hydropower in 2010. China is the largest hydroelectricity producer, with 721 terawatt-hours of production in 2010, representing around 17 percent of domestic electricity use. There are now three hydroelectricity plants larger than 10 GW: the Three Gorges Dam in China, Itaipu Dam across the Brazil/Paraguay border, and Guri Dam in Venezuela. The cost of hydroelectricity is low, making it a competitive source of renewable electricity. The average cost of electricity from a hydro plant larger than 10 megawatts is 3 to 5 U.S. cents per kilowatt-hour.
Geothermal power capacity grew from around 1 GW in 1975 to almost 10 GW in 2008. The United States is the world leader in terms of installed capacity, representing 3.1 GW. Other countries with significant installed capacity include the Philippines (1.9 GW), Indonesia (1.2 GW), Mexico (1.0 GW), Italy (0.8 GW), Iceland (0.6 GW), Japan (0.5 GW), and New Zealand (0.5 GW). In some countries, geothermal power accounts for a significant share of the total electricity supply, such as in the Philippines, where geothermal represented 17 percent of the total power mix at the end of 2008.
Many solar photovoltaic power stations have been built, mainly in Europe. As of July 2012, the largest photovoltaic (PV) power plants in the world are the Agua Caliente Solar Project (USA, 247 MW), Charanka Solar Park (India, 214 MW), Golmud Solar Park (China, 200 MW), Perovo Solar Park (Russia 100 MW), Sarnia Photovoltaic Power Plant (Canada, 97 MW), Brandenburg-Briest Solarpark (Germany 91 MW), Solarpark Finow Tower (Germany 84.7 MW), Montalto di Castro Photovoltaic Power Station (Italy, 84.2 MW), Eggebek Solar Park (Germany 83.6 MW), Senftenberg Solarpark (Germany 82 MW), Finsterwalde Solar Park (Germany, 80.7 MW), Okhotnykovo Solar Park (Russia, 80 MW), Lopburi Solar Farm (Thailand 73.16 MW), Rovigo Photovoltaic Power Plant (Italy, 72 MW), and the Lieberose Photovoltaic Park (Germany, 71.8 MW).
There are also many large plants under construction. The Desert Sunlight Solar Farm under construction in Riverside County, California and Topaz Solar Farm being built in San Luis Obispo County, California are both 550 MW solar parks that will use thin-film solar photovoltaic modules made by First Solar. The Blythe Solar Power Project is a 500 MW photovoltaic station under construction in Riverside County, California. The California Valley Solar Ranch (CVSR) is a 250 megawatt (MW) solar photovoltaic power plant, which is being built by SunPower in the Carrizo Plain, northeast of California Valley. The 230 MW Antelope Valley Solar Ranch is a First Solar photovoltaic project which is under construction in the Antelope Valley area of the Western Mojave Desert, and due to be completed in 2013. The Mesquite Solar project is a photovoltaic solar power plant being built in Arlington, Maricopa County, Arizona, owned by Sempra Generation. Phase 1 will have a nameplate capacity of 150 megawatts.
Some of the second-generation renewables, such as wind power, have high potential and have already realised relatively low production costs. Global wind power installations increased by 35,800 MW in 2010, bringing total installed capacity up to 194,400 MW, a 22.5% increase on the 158,700 MW installed at the end of 2009. The increase for 2010 represents investments totalling €47.3 billion (US$65 billion) and for the first time more than half of all new wind power was added outside of the traditional markets of Europe and North America, mainly driven, by the continuing boom in China which accounted for nearly half of all of the installations at 16,500 MW. China now has 42,300 MW of wind power installed. Wind power accounts for approximately 19% of electricity generated in Denmark, 9% in Spain and Portugal, and 6% in Germany and the Republic of Ireland. In Australian state of South Australia wind power, championed by Premier Mike Rann (2002–2011), now comprises 26% of the state's electricity generation, edging out coal fired power. At the end of 2011 South Australia, with 7.2% of Australia's population, had 54%of the nation's installed wind power capacity. Wind power's share of worldwide electricity usage at the end of 2014 was 3.1%. These are some of the largest wind farms in the world:
As of 2014, the wind industry in the USA is able to produce more power at lower cost by using taller wind turbines with longer blades, capturing the faster winds at higher elevations. This has opened up new opportunities and in Indiana, Michigan, and Ohio, the price of power from wind turbines built 300 feet to 400 feet above the ground can now compete with conventional fossil fuels like coal. Prices have fallen to about 4 cents per kilowatt-hour in some cases and utilities have been increasing the amount of wind energy in their portfolio, saying it is their cheapest option.

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