Wikipedia receives between 25,000 and 60,000 page requests per second, depending on time of day. As of 2019, page requests are first passed to a front-end layer of Varnish caching servers. Further statistics, based on a publicly available 3-month Wikipedia access trace, are available. Requests that cannot be served from the Varnish cache are sent to load-balancing servers running the Linux Virtual Server software, which in turn pass them to one of the Apache web servers for page rendering from the database. The web servers deliver pages as requested, performing page rendering for all the language editions of Wikipedia. To increase speed further, rendered pages are cached in a distributed memory cache until invalidated, allowing page rendering to be skipped entirely for most common page accesses.
Wikipedia seeks to create a summary of all human knowledge in the form of an online encyclopedia, with each topic covered encyclopedically in one article. Since it has terabytes of disk space, it can have far more topics than can be covered by any printed encyclopedia. The exact degree and manner of coverage on Wikipedia is under constant review by its editors, and disagreements are not uncommon (see deletionism and inclusionism). Wikipedia contains materials that some people may find objectionable, offensive, or pornographic. The 'Wikipedia is not censored' policy has sometimes proved controversial: in 2008, Wikipedia rejected an online petition against the inclusion of images of Muhammad in the English edition of its Muhammad article, citing this policy. The presence of politically, religiously, and pornographically sensitive materials in Wikipedia has led to the censorship of Wikipedia by national authorities in China and Pakistan, amongst other countries.
More InfoArticles for traditional encyclopedias such as Encyclopædia Britannica are carefully and deliberately written by experts, lending such encyclopedias a reputation for accuracy. However, a peer review in 2005 of forty-two scientific entries on both Wikipedia and Encyclopædia Britannica by the science journal Nature found few differences in accuracy, and concluded that "the average science entry in Wikipedia contained around four inaccuracies; Britannica, about three." Reagle suggested that while the study reflects "a topical strength of Wikipedia contributors" in science articles, "Wikipedia may not have fared so well using a random sampling of articles or on humanities subjects." Others raised similar critiques. The findings by Nature were disputed by Encyclopædia Britannica, and in response, Nature gave a rebuttal of the points raised by Britannica. In addition to the point-for-point disagreement between these two parties, others have examined the sample size and selection method used in the Nature effort, and suggested a "flawed study design" (in Nature's manual selection of articles, in part or in whole, for comparison), absence of statistical analysis (e.g., of reported confidence intervals), and a lack of study "statistical power" (i.e., owing to small sample size, 42 or 4 × 101 articles compared, vs >105 and >106 set sizes for Britannica and the English Wikipedia, respectively).
More InfoThe operation of Wikipedia depends on MediaWiki, a custom-made, free and open source wiki software platform written in PHP and built upon the MySQL database system. The software incorporates programming features such as a macro language, variables, a transclusion system for templates, and URL redirection. MediaWiki is licensed under the GNU General Public License and it is used by all Wikimedia projects, as well as many other wiki projects. Originally, Wikipedia ran on UseModWiki written in Perl by Clifford Adams (Phase I), which initially required CamelCase for article hyperlinks; the present double bracket style was incorporated later. Starting in January 2002 (Phase II), Wikipedia began running on a PHP wiki engine with a MySQL database; this software was custom-made for Wikipedia by Magnus Manske. The Phase II software was repeatedly modified to accommodate the exponentially increasing demand. In July 2002 (Phase III), Wikipedia shifted to the third-generation software, MediaWiki, originally written by Lee Daniel Crocker.
More InfoIn January 2013, 274301 Wikipedia, an asteroid, was named after Wikipedia; in October 2014, Wikipedia was honored with the Wikipedia Monument; and, in July 2015, Wikipedia became available as 7,473 books for $500,000. In 2019, a species of flowering plant was named Viola wikipedia. In April 2019, an Israeli lunar lander, Beresheet, crash landed on the surface of the Moon carrying a copy of nearly all of the English Wikipedia engraved on thin nickel plates; experts say the plates likely survived the crash. In June 2019, scientists reported that all 16 GB of article text from the English Wikipedia have been encoded into synthetic DNA.
More InfoIn 2008, researchers at Carnegie Mellon University found that the quality of a Wikipedia article would suffer rather than gain from adding more writers when the article lacked appropriate explicit or implicit coordination. For instance, when contributors rewrite small portions of an entry rather than making full-length revisions, high- and low-quality content may be intermingled within an entry. Roy Rosenzweig, a history professor, stated that American National Biography Online outperformed Wikipedia in terms of its "clear and engaging prose", which, he said, was an important aspect of good historical writing. Contrasting Wikipedia's treatment of Abraham Lincoln to that of Civil War historian James McPherson in American National Biography Online, he said that both were essentially accurate and covered the major episodes in Lincoln's life, but praised "McPherson's richer contextualization [...] his artful use of quotations to capture Lincoln's voice [...] and [...] his ability to convey a profound message in a handful of words." By contrast, he gives an example of Wikipedia's prose that he finds "both verbose and dull". Rosenzweig also criticized the "waffling—encouraged by the NPOV policy—[which] means that it is hard to discern any overall interpretive stance in Wikipedia history". While generally praising the article on William Clarke Quantrill, he quoted its conclusion as an example of such "waffling", which then stated: "Some historians [...] remember him as an opportunistic, bloodthirsty outlaw, while others continue to view him as a daring soldier and local folk hero."
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