[[TheHitchhikersGuideToTheGalaxy http://tvtropes.org/pmwiki/pub/images/Deep_Thought.png]]
[[caption-width:320:Deep Thought]]

Older media dealing with computers were predicated on the idea of the MasterComputer. A science fiction {{dystopia}} holding humanity in chains could be liberated by finding the key mainframe and either shutting it down or destroying it. The main character often destroys the key mainframe by asking it a [[LogicBomb paradoxical or philosophical question]] or by reading [[StrawVulcan poetry]] to it, causing it to self-destruct. A major, world spanning corporation could be brought to its knees by sabotaging its mainframe. Governments could be held hostage by anyone who controlled the single computer and rendered its data inaccessible.

In some SciFi, this can allow you to create a computer of impressively imposing size, which you can [[StuffBlowingUp blow up]] in one go.

Largely a DiscreditedTrope today due to the growth of networks and multiply redundant systems; and, maybe, due to the fall of the Soviet Union, that simply loved centralized everything. It should be noted however that centralized computing is a recurring paradigm these days thanks to virtualization and terminal services. See also ComputerEqualsTapedrive.

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[[foldercontrol]]

!!Examples

[[folder:Anime & Manga]]
* "Big Mama", a.k.a. "Toy", the OmnicidalManiac dictator of the world of ''Grey''.
* In ''DirtyPair'', [[HeroesRUs the WWWA]] is run by a "Central Computer", which decides which agents get assigned to a case -- and also infallibly clears the Lovely Angels of blame for [[MikeNelsonDestroyerOfWorlds the latest disaster to occur in their wake.]]
* The MAGI trio of super-computers from ''NeonGenesisEvangelion,'' who are essentially the shadow government of Tokyo-3. Unusually for computers (or humans, really) in such a position, at ''no'' point in the series do they turn evil. (Although they do get infected by a nasty virus in one episode.)
* Leopard, the rather talky AI who runs the abandoned space colony in ''SoraWoKakeruShoujo''. He's also a little unhinged.
* Subverted in ''{{Toward the Terra}}''. It turns out the "Mother" mainframe the Mu try to disable is actually a scale-free network.
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[[folder:Films]]
* ''ColossusTheForbinProject'' had one mainframe buried in a mountain, and its Soviet counterpart composed of a network of smaller computers.
* Conspicuously absent in ''{{Terminator}} 3''. [[spoiler:It just shows how widespread this trope is that the revelation that there was no central Skynet server to destroy was the film's big plot twist. Though it does raise questions about how Skynet survived the massive nuclear attack that it unleashed.]]
** This was due to the changes in the timeline; the John Connor who sent back Kyle Reese did win the war this way. ''T3'''s Connor knew that, and was acting on information that was no longer accurate.
***Also, given that the internet was originally developed as a military redundant communications network that could still function even in the event of a devastating war that destroyed large parts of it...
* The WOPR (War Operation Plan Response) computer in the movie ''[[WarGames War Games]]''.
* HAL 9000 in ''[[TwoThousandOneASpaceOdyssey 2001: A Space Odyssey]]''.
* V.I.K.I. from the film loosely based on ''I, Robot''.
* The Red Queen from ''ResidentEvil''.
* The Master Control Program from ''{{Tron}}''.
** In a ''[=~Dexter's Laboratory~=]'' parody, it was replaced with a program actually called "Master Computer".
* ''EagleEye'' has [[spoiler: ARIIA, the signals-intelligence computer that skirts the line by being DangerouslyGenreSavvy enough to try to upload herself to a satellite backup.]]
* ''AndromedaStrain'' had all of Wildfire's computer terminals connected to the main computer on level one. Computations were conducted by the main computer on a timesharing system.
** Justified since the original book was written in 1969, and that's how computers were deployed back then.
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[[folder:Literature]]
* AM from Harlan Ellison's ''{{I Have no Mouth and I Must Scream}}'', originally named Allied Mastercomputer, then Adaptive Manipulator, then Agressive Menace, and finally just AM (as in ''I Think Therefore I Am''). His mainframe was implied to span the entire planet, and he was essentially a god within it -- but AM is [[spoiler:three networked mainframes with thousands of redundant systems]]. In the videogame, AM [[spoiler:is eventually defeated by collapsing the entire cave system, i.e, the world.]]
* Multivac in early IsaacAsimov short stories.
** In ''The Last Question,'' (readable [[http://www.multivax.com/last_question.html here]]) the story takes place over an indeterminate length of time, where people ask the same question (how to prevent the heat death of the universe) of Multivac and every one of its descendents. This ends with "Man," the personification of a true, perfect unification of *every last human being in the universe,* asks the question of the final version of the AC. It still can't answer... [[spoiler:but when said heat death does occur, it merges with Man, spends an undefined amount of time processing, and then revitalises the universe by declaring "Let There Be Light".]]
* Mycroft Holmes (Mike) in Robert Heinlein's ''The Moon is a Harsh Mistress''. [[LampshadeHanging Lampshaded]] when Manny rants about how stupid it is to have vital life support functions controlled by one master computer instead of local redundant failsafe controls. (But then the Lunar colony was originally a prison, so having life-support under centralized control meant that the jailers could shut it off to any section if the prisoners got rambunctious.)
* Parodied in the KimNewman short story "Tomorrow Town": a community of 1970s futurists attempt to build one of these and construct an AI, but are unsuccessful, and what they come up with is essentially a large contemporary computer with lots of bits added on; i.e., not bad at adding things up, but pretty crappy at almost everything else. Ironically, the villain's attempt to destroy the community by overloading this was thwarted by the computer itself, which promptly ran an error program and alerted the heroes to what they needed to do in order to stop it.
* [=UniComp=] in ''ThisPerfectDay''.
* Omnius in the Expanded ''Dune'' Series. In the prequels dealing with the Butlerian Jihad, they're networked with each other, but because they're separated by large stretches of space, the travel time between updating allows opportunity for sabotage, and then destruction of each network. In the sequels, there's only one Master Computer that has to be dealt with (admittedly, having someone who's effectively god on your side doesn't hurt either).
* Covered from the perspective of an [[AlternateHistory alternate timeline's]] Special forces soldier in S.M. Stirling's ''Drakon''. In his timeline there has been a Cold War many times worse than ours. They only use central computers, with a few terminals hardwired in. When he visits a timeline like ours, and looks at the internet, he is astounded at so many separate processing units protected by nothing more than passwords and encryption. This would scare the hell out of any competent espionage agency in his timeline.
* The ''{{Destroyer}}'' has Friend and The Folcroft Four. The Folcroft Four are massive storage banks for information that Dr. Smith gets from lurking.
* ''The Cosmic Computer'' in the [[HBeamPiper H. Beam Piper]] novel of the same name.
* The "Well of Souls" in JackChalker's WellWorld series is the MasterComputer for the ''entire universe.''
* The Central Arcadian Computer in ''[[FightingFantasy Rebel Planet]]''
* In the ''Hitch-Hikers Guide to the Galaxy'' you had the greatest computer in the universe designed by the second greatest computer in the univers "Deep Thought" whose sole purpose was to discover the question to the answer to the ultimate question of life the universe and everything.
** Deep Thought was so powerful that when it was first plugged in, it started with "I think, therefore I am", and got around to deducing the existence of rice pudding and income tax before anyone got around to plugging in its databanks.
*** Then Deep Thought created the plans for an even bigger computer, one the size of a planet... in fact it ''is'' a planet. True to form, the computer gets blown up. [[ThisIsSparta The. Computer. Is.]] [[YouShouldKnowThisAlready Earth.]]
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[[folder:Live Action TV]]
* ''Star Trek''. Captain Kirk is on the Ten Most Wanted list of every computer manufacturer in the known universe.
** So is the [[DoctorWho Doctor]].
* ''[[BlakesSeven Blakes Seven]]'' had the Federation's Star One.
* "The General" in ''ThePrisoner'' (self-destructed when asked the question "Why?")
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[[folder:Tabletop Games]]
* In the RPG ''{{Paranoia}}'', [[strike: The Computer]] Friend Computer is the [[strike:insane]] happy and perfect controller of [[ElaborateUndergroundBase Alpha Complex]].
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[[folder:Video Games]]
* Despite ''MegaManBattleNetwork'' being all about computers TwentyMinutesIntoTheFuture, they still have the "Mother Computer", the invasion of which was a chapter in ''Battle Network 2''.
** Happens again in the next game with the [[spoiler:whole Undernet being on One. Frigging. Computer. This in itself requires an insane amount of FridgeLogic and Internal [[RetCon Retconning]].]]
* ''SystemShock'' has SHODAN, the AI given complete sentience through hacking. Although SHODAN is confined to the space station the game is set on, the player must make their way (eventually) to the bridge of the station in order to attack SHODAN's "main system" and kill the AI completely, thus implying that SHODAN is a master computer-type with fully control over the station's systems. In addition, one of her plans is to [[spoiler: download herself to the Earth computer network, thus gaining control over the entire world and also circumventing the master computer weakness]].
** And subverted, because [[spoiler: in ''SystemShock2' it turns out that the processing components on one of the parts of the space station the protagonist from the first game jettisoned are enough to form a new incarnation of SHODAN. Seems like she was into redundant systems after all...]]
* [=GLaDOS=] from ''{{Portal}}'' is this trope to a T. She also follows the SHODAN sub-trope, in that [[spoiler: after you destroy what seems to be her mainframe, a room of spare components activate and she starts to sing that she is still alive.]] Though she may be [[MindScrew lying]].
* Mother Brain, and later the Aurora Units, from the ''{{Metroid}}'' series. Mother Brain runs both the Space Pirate organization and the entirety of the planet Zebes, while the Federation is utterly dependent on its Aurora mainframes for its military planning. The failure and destruction of these devices is a recurring theme throughout the games.
** Note that these computers are [[OrganicTechnology organic]]- essentially giant, genetically engineered brains, hence a single master system is kind of a necessity.
* Consciously averted in ''MassEffect''. Since AIIsACrapshoot, no computer is ever designed with more than rudimentary "virtual" intelligence (shown to be little better than a modern software assistant), and most information flows through a galactic Internet-like network. Naturally, when machine sentience does turn up ([[EverythingTryingToKillYou and try to kill you]]), it's almost always structured around massively parallel processing (the rogue VI on Luna, the geth, etc.).
** Except it is used straight as well: [[spoiler: The AI funneling funds from the Quasar machines is housed in a single "quantum blue-box in the back of The Emporium shop.]]
* At one point in ''{{Marathon}} 2'', you are tasked with destroying the hardware that Durandal has been using to store himself. Turns out to be a subversion, though, as Durandal is back no worse for the wear a couple of weeks later. The rest of the time, the trope is averted: a Rampant AI in the Jealous stage is noted to be near-impossible to kill, since it usually inhabits a planet-wide network of computers (or more, if it can) by that point.
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[[folder:Web Comics]]
* In ''{{SSDD}}'', most artificial intelligences cannot be copied due to their use of Quantum computing and are restricted to one highly powerful machine (though they can interact with other nodes remotely), whereas the Oracle can be copied due to being digital and has spread to as many different systems as it can, even possessing other [=AIs=]
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[[folder:Western Animation]]
* Loretta, from the ''{{Duckman}}'' episode "The Gripes Of Wrath".
* ''CodeLyoko'': The Supercomputer is not just containing the {{Cyberspace}} of Lyoko and all the programs created by Franz Hopper, but is also a prison for the BigBad XANA. The latter isn't happy about this and spends the whole Season 2 trying to escape on the Net so that the heroes cannot any more CutTheJuice on him.
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[[folder:Comics]]
* An early ''StrontiumDog'' strip had Johnny and Wulf working for, then going up against an insane computer which had seized control of a planet in an {{allegory}} for the fall of the Roman Empire.
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[[folder:Real Life]]
* The U.S. military created [=ArpaNet=], which later became the Internet, specifically to prevent any one computer failure from crippling the country's armed forces.
* Much numerical research is done in this way, with a small number of machines being operated through the internet by a large number of operators. This means that when one machine fails, several people are unable to get their programs run.
* To a somewhat lesser extent, "cloud computing", where the heavy lifting (so to speak) is done by a centralized internet-based server, and the results sent out to client computers that basically act like the old mainframe/terminal scheme from the early days of computing.
* [[http://en.wikipedia.org/wiki/Project_Cybersyn Project Cybersyn]], an attempt by President Salvadore Allende to use a centralized network of computers to run the Chilean economy. The whole plan looked like it was ripped out of a bad science fiction movie, right down to the zeerust control room.
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