History of computing hardware: Difference between revisions

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The '''history of computing hardware''' spans the developments from early devices used for simple calculations to today's complex computers, encompassing advancements in both analog and digital technology.
 
The first aids to computation were purely mechanical devices which required the operator to set up the initial values of an elementary [[arithmetic]] operation, then manipulate the device to obtain the result. In later stages, computing devices began representing numbers in continuous forms, such as by distance along a scale, rotation of a shaft, or a specific voltage level. Numbers could also be represented in the form of digits, automatically manipulated by a mechanism. Although this approach generally required more complex mechanisms, it greatly increased the precision of results. The development of transistor technology, followed by the invention of integrated circuit chips, led to revolutionary breakthroughs.

Transistor-based computers and, later, integrated circuit-based computers enabled digital systems to gradually replace analog systems, increasing both efficiency and processing power. [[MOSFET|Metal-oxide-semiconductor]] (MOS) [[large-scale integration]] (LSI) then enabled [[semiconductor memory]] and the [[microprocessor]], leading to another key breakthrough, the miniaturized [[personal computer]] (PC), in the 1970s. The cost of computers gradually became so low that personal computers by the 1990s, and then [[mobile computing|mobile computers]] ([[smartphone]]s and [[tablet computer|tablets]]) in the 2000s, became ubiquitous.
 
==Early devices==
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{{Main|Analytical Engine}}
[[File:Difference engine plate 1853.jpg|thumb|A portion of [[Charles Babbage|Babbage]]'s [[Difference Engine]] ]][[File:AnalyticalMachine Babbage London.jpg|thumb|left|Trial model of a part of the Analytical Engine, built by Babbage, as displayed at the Science Museum, London]]
The [[Industrial Revolution]] (late 18th to early 19th century) had a significant impact on the evolution of computing hardware, as the era's rapid advancements in machinery and manufacturing laid the groundwork for mechanized and automated computing. Industrial needs for precise, large-scale calculations—especially in fields such as navigation, engineering, and finance—prompted innovations in both design and function, setting the stage for devices like [[Charles Babbage|Charles Babbage's]] [[difference engine]] (1822).<ref>{{Cite book |last=Babbage |first=Charles |url=http://dx.doi.org/10.1017/cbo9781139103671 |title=Passages from the Life of a Philosopher |date=2011-10-12 |publisher=Cambridge University Press |doi=10.1017/cbo9781139103671 |isbn=978-1-108-03788-4}}</ref><ref>{{Cite book |last=Babbage |first=Charles |url=http://dx.doi.org/10.1017/cbo9780511696374 |title=On the Economy of Machinery and Manufactures |date=2010-03-04 |publisher=Cambridge University Press |doi=10.1017/cbo9780511696374 |isbn=978-1-108-00910-2}}</ref> This mechanical device was intended to automate the calculation of polynomial functions and represented one of the earliest applications of computational logic.<ref>{{Cite journal |last=Hutton |first=D.M. |date=2002-08-01 |title=The Difference Engine: Charles Babbage and the Quest to Build the First Computer |url=http://dx.doi.org/10.1108/k.2002.06731fae.009 |journal=Kybernetes |volume=31 |issue=6 |doi=10.1108/k.2002.06731fae.009 |issn=0368-492X|url-access=subscription }}</ref>
 
Babbage, often regarded as the "father of the computer," envisioned a fully mechanical system of gears and wheels, powered by steam, capable of handling complex calculations that previously required intensive manual labor.<ref>{{Cite journal |last=Tropp |first=Henry S. |date=December 1975 |title=''The Origins of Digital Computers: Selected Papers''. Brian Randell |url=http://dx.doi.org/10.1086/351520 |journal=Isis |volume=66 |issue=4 |pages=572–573 |doi=10.1086/351520 |issn=0021-1753|url-access=subscription }}</ref> His difference engine, designed to aid navigational calculations, ultimately led him to conceive the [[analytical engine]] in 1833.<ref>{{Cite journal |last1=W. |first1=J. W. |last2=Hyman |first2=Anthony |date=April 1986 |title=Charles Babbage, Pioneer of the Computer. |url=http://dx.doi.org/10.2307/2008013 |journal=Mathematics of Computation |volume=46 |issue=174 |pages=759 |doi=10.2307/2008013 |jstor=2008013 |issn=0025-5718|url-access=subscription }}</ref> This concept, far more advanced than his difference engine, included an [[arithmetic logic unit]], control flow through conditional branching and loops, and integrated memory.<ref>{{Cite book |last1=Campbell-Kelly |first1=Martin |last2=Aspray |first2=William |last3=Ensmenger |first3=Nathan |last4=Yost |first4=Jeffrey R. |date=2018-04-20 |title=Computer |url=http://dx.doi.org/10.4324/9780429495373 |doi=10.4324/9780429495373|isbn=978-0-429-49537-3 }}</ref> Babbage's plans made his analytical engine the first general-purpose design that could be described as [[Turing completeness|Turing-complete]] in modern terms.<ref>{{Citation |last=Turing |first=Alan |title=Computing Machinery and Intelligence (1950) |date=2004-09-09 |work=The Essential Turing |pages=433–464 |url=http://dx.doi.org/10.1093/oso/9780198250791.003.0017 |access-date=2024-10-30 |publisher=Oxford University PressOxford |doi=10.1093/oso/9780198250791.003.0017 |isbn=978-0-19-825079-1|url-access=subscription }}</ref><ref>{{Cite book |last=Davis |first=Martin |date=2018-02-28 |title=the Universal Computer |url=http://dx.doi.org/10.1201/9781315144726 |doi=10.1201/9781315144726|isbn=978-1-315-14472-6 }}</ref>
 
The analytical engine was programmed using [[Punched card input/output|punched cards]], a method adapted from the [[Jacquard machine|Jacquard loom]] invented by [[Joseph Marie Jacquard]] in 1804, which controlled textile patterns with a sequence of punched cards.<ref>{{Cite journal |last1=d'Ucel |first1=Jeanne |last2=Dib |first2=Mohammed |date=1958 |title=Le métier à tisser |url=http://dx.doi.org/10.2307/40098349 |journal=Books Abroad |volume=32 |issue=3 |pages=278 |doi=10.2307/40098349 |jstor=40098349 |issn=0006-7431|url-access=subscription }}</ref> These cards became foundational in later computing systems as well.<ref>{{Cite book |last=Heide |first=Lars |url=http://dx.doi.org/10.1353/book.3454 |title=Punched-Card Systems and the Early Information Explosion, 1880–1945 |date=2009 |publisher=Johns Hopkins University Press |doi=10.1353/book.3454 |isbn=978-0-8018-9143-4}}</ref> Babbage's machine would have featured multiple output devices, including a printer, a curve plotter, and even a bell, demonstrating his ambition for versatile computational applications beyond simple arithmetic.<ref>{{Cite journal |last=Bromley |first=A.G. |date=1998 |title=Charles Babbage's Analytical Engine, 1838 |url=http://dx.doi.org/10.1109/85.728228 |journal=IEEE Annals of the History of Computing |volume=20 |issue=4 |pages=29–45 |doi=10.1109/85.728228 |issn=1058-6180|url-access=subscription }}</ref>
 
[[Ada Lovelace]] expanded on Babbage's vision by conceptualizing algorithms that could be executed by his machine.<ref>{{Cite journal |last=Toole |first=Betty Alexandra |date=March 1991 |title=Ada, an analyst and a metaphysician |url=http://dx.doi.org/10.1145/122028.122031 |journal=ACM SIGAda Ada Letters |volume=XI |issue=2 |pages=60–71 |doi=10.1145/122028.122031 |issn=1094-3641|url-access=subscription }}</ref> Her notes on the analytical engine, written in the 1840s, are now recognized as the earliest examples of computer programming.<ref>{{Cite book |last1=Howard |first1=Emily |last2=De Roure |first2=David |chapter=Turning numbers into notes |date=2015 |title=Ada Lovelace Symposium 2015- Celebrating 200 Years of a Computer Visionary on - Ada Lovelace Symposium '15 |chapter-url=http://dx.doi.org/10.1145/2867731.2867746 |___location=New York, New York, USA |publisher=ACM Press |pages=13 |doi=10.1145/2867731.2867746|isbn=978-1-4503-4150-9 }}</ref> Lovelace saw potential in computers to go beyond numerical calculations, predicting that they might one day generate complex musical compositions or perform tasks like language processing.<ref>{{Cite journal |last1=Haugtvedt |first1=Erica |last2=Abata |first2=Duane |title=Ada Lovelace: First Computer Programmer and Hacker? |url=http://dx.doi.org/10.18260/1-2--36646 |journal=2021 ASEE Virtual Annual Conference Content Access Proceedings |date=2021 |publisher=ASEE Conferences |doi=10.18260/1-2--36646}}</ref>
 
Though Babbage's designs were never fully realized due to technical and financial challenges, they influenced a range of subsequent developments in computing hardware. Notably, in the 1890s, [[Herman Hollerith]] adapted the idea of punched cards for automated data processing, which was utilized in the U.S. Census and sped up data tabulation significantly, bridging industrial machinery with data processing.<ref>{{Cite thesis |last=Blodgett |first=John H. |title=Herman Hollerith, data processing pioneer |date=1968 |publisher=Drexel University Libraries |doi=10.17918/00004750 |url=http://dx.doi.org/10.17918/00004750|url-access=subscription }}</ref>
 
The Industrial Revolution's advancements in mechanical systems demonstrated the potential for machines to conduct complex calculations, influencing engineers like [[Leonardo Torres Quevedo]] and [[Vannevar Bush]] in the early 20th century. Torres Quevedo designed an electromechanical machine with floating-point arithmetic,<ref>{{Citation |last=Torres y Quevedo |first=Leonardo |title=Essays on Automatics |date=1982 |work=The Origins of Digital Computers |pages=89–107 |url=http://dx.doi.org/10.1007/978-3-642-61812-3_6 |access-date=2024-10-30 |place=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg |doi=10.1007/978-3-642-61812-3_6 |isbn=978-3-642-61814-7|url-access=subscription }}</ref> while Bush's later work explored electronic digital computing.<ref>{{Citation |title=6 Vannevar Bush, from "As We May Think" (1945) |date=2021 |work=Information |publisher=Columbia University Press |doi=10.7312/hayo18620-032 |isbn=978-0-231-54654-6|doi-access=free }}</ref> By the mid-20th century, these innovations paved the way for the first fully electronic computers.<ref>{{Cite book |last1=Haigh |first1=Thomas |url=http://dx.doi.org/10.7551/mitpress/11436.001.0001 |title=A New History of Modern Computing |last2=Ceruzzi |first2=Paul E. |date=2021-09-14 |publisher=The MIT Press |doi=10.7551/mitpress/11436.001.0001 |isbn=978-0-262-36648-9}}</ref>
 
==Analog computers==
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[[File:Z3 Deutsches Museum.JPG|thumb|left|Replica of [[Konrad Zuse|Zuse]]'s [[Z3 (computer)|Z3]], the first fully automatic, digital (electromechanical) computer]]
In 1941, Zuse followed his earlier machine up with the [[Z3 (computer)|Z3]],<ref name="Part 4 Zuse"/> the world's first working [[electromechanical]] [[Computer programming|programmable]], fully automatic digital computer.<ref>{{cite news|title=A Computer Pioneer Rediscovered, 50 Years On |newspaper=The New York Times |url=https://www.nytimes.com/1994/04/20/news/20iht-zuse.html |date=20 April 1994 |access-date=2017-02-16 |archive-date=2016-11-04 |archive-url=https://web.archive.org/web/20161104051054/http://www.nytimes.com/1994/04/20/news/20iht-zuse.html|url-status=live}}</ref> The Z3 was built with 2000 [[relay]]s, implementing a 22-[[bit]] [[Word (computer architecture)|word length]] that operated at a [[clock rate|clock frequency]] of about 5–10&nbsp;[[Hertz|Hz]].{{sfn|Zuse|1993|p=55}} Program code and data were stored on punched [[celluloid|film]]. It was quite similar to modern machines in some respects, pioneering numerous advances such as [[floating-point arithmetic|floating-point numbers]]. Replacement of the hard-to-implement decimal system (used in [[Charles Babbage]]'s earlier design) by the simpler [[binary number|binary]] system meant that Zuse's machines were easier to build and potentially more reliable, given the technologies available at that time.<ref>{{cite web |url=https://www.crash-it.com/crash/index.php?page=73 |archive-url=https://web.archive.org/web/20080318184915/http://www.crash-it.com/crash/index.php?page=73 |url-status=dead |archive-date=2008-03-18 |title=Zuse |work=Crash! The Story of IT}}</ref> TheDespite lacking explicit conditional execution, the Z3 was proven to have been a theoretically [[Turing machine|Turing-complete machine]] in 1998 by [[Raúl Rojas]].<ref>{{Cite book|last=Rojas|first=Raúl|title=How to Make Zuse's Z3 a Universal Computer |date=1998 |citeseerx=10.1.1.37.665}}</ref> In two 1936 [[patent]] applications, Zuse also anticipated that machine instructions could be stored in the same storage used for data—the key insight of what became known as the [[von Neumann architecture]], first implemented in 1948 in America in the [[Mechanical computer#Electro-mechanical computers|electromechanical]] [[IBM SSEC]] and in Britain in the fully electronic [[Manchester Baby]].<ref>{{cite journal |title=Electronic Digital Computers |journal=Nature |last1=Williams |first1=F. C. |last2=Kilburn |first2=T. |date=25 September 1948 |volume=162 |issue=4117 |page=487 |bibcode=1948Natur.162..487W |doi=10.1038/162487a0 |s2cid=4110351 |doi-access=free }}</ref>
 
Zuse suffered setbacks during World War II when some of his machines were destroyed in the course of [[Allies of World War II|Allied]] bombing campaigns. Apparently his work remained largely unknown to engineers in the UK and US until much later, although at least IBM was aware of it as it financed his post-war startup company in 1946 in return for an option on Zuse's patents.
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In October 1947, the directors of [[J. Lyons and Co.|J. Lyons & Company]], a British catering company famous for its teashops but with strong interests in new office management techniques, decided to take an active role in promoting the commercial development of computers. The [[LEO computer|LEO I]] computer (Lyons Electronic Office) became operational in April 1951<ref>{{cite web | last = Lavington | first = Simon | title = A brief history of British computers: the first 25 years (1948–1973). | publisher = [[British Computer Society]] | url = http://www.bcs.org/server.php? | access-date = 10 January 2010 | archive-date = 2010-07-05 | archive-url = https://web.archive.org/web/20100705050757/http://www.bcs.org/server.php | url-status = dead }}</ref> and ran the world's first regular routine office computer [[job (software)|job]]. On 17 November 1951, the J. Lyons company began weekly operation of a bakery valuations job on the LEO – the first business [[:Category:Application software|application]] to go live on a stored-program computer.{{efn|{{harvnb|Martin|2008|p=24}} notes that [[David Caminer]] (1915–2008) served as the first corporate electronic systems analyst, for this first business computer system. LEO would calculate an employee's pay, handle billing, and other office automation tasks.}}
 
In June 1951, the [[UNIVAC I]] (Universal Automatic Computer) was delivered to the [[United States Census Bureau|U.S. Census Bureau]]. Remington Rand eventually sold 46 machines at more than {{US$|1 million}} each (${{Formatprice|{{Inflation|US|1000000|1951|r=-4}}|0}} as of {{CURRENTYEARinflation/year|US}}).{{Inflation-fn|US}} UNIVAC was the first "mass-produced" computer. It used 5,200 vacuum tubes and consumed {{val|125|ul=kW}} of power. Its primary storage was [[Sequential access|serial-access]] mercury delay lines capable of storing 1,000 words of 11 decimal digits plus sign (72-bit words).
 
In 1952, [[Groupe Bull|Compagnie des Machines Bull]] released the [[Bull Gamma 3|Gamma 3]] computer, which became a large success in Europe, eventually selling more than 1,200 units, and the first computer produced in more than 1,000 units.<ref name=":1">{{Cite journal |last=Leclerc |first=Bruno |date=January 1990 |title=From Gamma 2 to Gamma E.T.: The Birth of Electronic Computing at Bull |url=https://ieeexplore.ieee.org/document/4637512 |journal=Annals of the History of Computing |volume=12 |issue=1 |pages=5–22 |doi=10.1109/MAHC.1990.10010 |s2cid=15227017 |issn=0164-1239}}</ref> The Gamma 3 had innovative features for its time including a dual-mode, software switchable, BCD and binary ALU, as well as a hardwired floating-point library for scientific computing.<ref name=":1" /> In its E.T configuration, the Gamma 3 drum memory could fit about 50,000 instructions for a capacity of 16,384 words (around 100&nbsp;kB), a large amount for the time.<ref name=":1" />
 
[[File:IBM-650-panel.jpg|thumb|right|Front panel of the [[IBM 650]] ]]
Compared to the UNIVAC, IBM introduced a smaller, more affordable computer in 1954 that proved very popular.{{efn|For example, Kara Platoni's article on [[Donald Knuth]] stated that "there was something special about the IBM 650".<ref>{{cite magazine |first=Kara |last=Platoni |title=Love at First Byte |magazine=Stanford Magazine |url=https://www.stanfordalumni.org/news/magazine/2006/mayjun/features/knuth.html |date=May–June 2006 |archive-url= https://web.archive.org/web/20060925022700/http://www.stanfordalumni.org/news/magazine/2006/mayjun/features/knuth.html |archive-date=2006-09-25 |url-status=dead}}</ref>}}<ref>
V. M. Wolontis (18 August 1955) "A Complete Floating-Decimal Interpretive System for the I.B.M. 650 Magnetic Drum Calculator—Case 20878" Bell Telephone Laboratories Technical Memorandum MM-114-37, Reported in IBM Technical Newsletter No. 11, March 1956, as referenced in {{cite journal |title=Wolontis-Bell Interpreter |publisher=IEEE |journal=Annals of the History of Computing |volume=8 |issue=1 |date=January–March 1986 |pages=74–76 |doi=10.1109/MAHC.1986.10008 |s2cid=36692260}}
</ref> The [[IBM 650]] weighed over {{val|900|u=kg}}, the attached power supply weighed around {{val|1350|u=kg}} and both were held in separate cabinets of roughly 1.5{{times}}0.9{{times}}{{val|1.8|u=meters}}. The system cost {{US$|500000}}<ref>{{cite book |last=Dudley |first=Leonard |title=Information Revolution in the History of the West |year=2008 |url= https://books.google.com/books?id=jLnPi5aYoJUC&pg=PA266 |isbn=978-1-84720-790-6 |publisher=Edward Elgar Publishing |page=266 |access-date=2020-08-30}}</ref> (${{Formatprice|{{Inflation|US|500000|1954|r=-4}}|0}} as of {{CURRENTYEARinflation/year|US}}) or could be leased for {{US$|3500}} a month (${{Formatprice|{{Inflation|US|3500|1954|r=-4}}|0}} as of {{CURRENTYEARinflation/year|US}}).{{Inflation-fn|US}} Its drum memory was originally 2,000 ten-digit words, later expanded to 4,000 words. Memory limitations such as this were to dominate programming for decades afterward. The program instructions were fetched from the spinning drum as the code ran. Efficient execution using drum memory was provided by a combination of hardware architecture – the instruction format included the address of the next instruction – and software: the [[Symbolic Optimal Assembly Program]], SOAP,<ref>{{Citation |last=IBM |title=SOAP II for the IBM 650 |year=1957 |id=C24-4000-0 |url= http://www.bitsavers.org/pdf/ibm/650/24-4000-0_SOAPII.pdf |access-date=2009-05-25 |archive-date=2009-09-20 |archive-url=https://web.archive.org/web/20090920081523/http://www.bitsavers.org/pdf/ibm/650/24-4000-0_SOAPII.pdf |url-status=live}}</ref> assigned instructions to the optimal addresses (to the extent possible by static analysis of the source program). Thus many instructions were, when needed, located in the next row of the drum to be read and additional wait time for drum rotation was reduced.
 
===Microprogramming===
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At the [[University of Manchester]], a team under the leadership of [[Tom Kilburn]] designed and built a machine using the newly developed [[transistor]]s instead of valves. Initially the only devices available were [[germanium]] [[point-contact transistor]]s, less reliable than the valves they replaced but which consumed far less power.{{sfn|Lavington|1998|pp=34–35}} Their first [[transistor computer|transistorized computer]], and the first in the world, was [[Manchester computers#Transistor Computer|operational by 1953]],{{sfn|Lavington|1998|p=37}} and a second version was completed there in April 1955.{{sfn|Lavington|1998|p=37}} The 1955 version used 200 transistors, 1,300 [[Solid-state electronics|solid-state]] [[diode]]s, and had a power consumption of 150 watts. However, the machine did make use of valves to generate its 125&nbsp;kHz clock waveforms and in the circuitry to read and write on its magnetic drum memory, so it was not the first completely transistorized computer.
 
That distinction goes to the [[Harwell CADET]] of 1955,<ref name="ieeexplore.ieee"/> built by the electronics division of the [[Atomic Energy Research Establishment]] at [[Harwell, Oxfordshire|Harwell]]. The design featured a 64-kilobyte magnetic drum memory store with multiple moving heads that had been designed at the [[National Physical Laboratory (United Kingdom)|National Physical Laboratory, UK]]. By 1953 this team had transistor circuits operating to read and write on a smaller magnetic drum from the [[Royal Radar Establishment]]. The machine used a low clock speed of only 58&nbsp;kHz to avoid having to use any valves to generate the clock waveforms.<ref>{{cite book |last=Cooke-Yarborough |first=E.H. |title=Introduction to Transistor Circuits |publisher=Oliver and Boyd |year=1957 |___location=Edinburgh}}</ref><ref name="ieeexplore.ieee">{{cite journal| title=Some early transistor applications in the UK| journal=Engineering Science & Education Journal| volume=7| issue=3| pages=100–106| year=1998| last1=Cooke-Yarborough| first1=E.H.| doi=10.1049/esej:19980301| doi-broken-date=712 DecemberJuly 20242025}}</ref>
 
CADET used 324-point-contact transistors provided by the UK company [[Standard Telephones and Cables]]; 76 [[Bipolar junction transistor|junction transistor]]s were used for the first stage amplifiers for data read from the drum, since point-contact transistors were too noisy. From August 1956, CADET was offering a regular computing service, during which it often executed continuous computing runs of 80 hours or more.<ref>{{cite book |last=Lavington |first=Simon |title=Early British Computers |publisher=Manchester University Press |year=1980 |url=https://ed-thelen.org/comp-hist/EarlyBritish-05-12.html#Ch-09 |isbn=0-7190-0803-4 |access-date=2014-01-07 |archive-date=2019-05-24 |archive-url=https://web.archive.org/web/20190524164254/http://ed-thelen.org/comp-hist/EarlyBritish-05-12.html#Ch-09 |url-status=live }}</ref><ref>{{Cite journal |doi= 10.1049/pi-b-1.1956.0076 |title=A transistor digital computer |journal=Proceedings of the IEE - Part B: Radio and Electronic Engineering |volume=103 |issue=3S |pages=364–370 |year=1956 |last1=Cooke-Yarborough |first1=E.H. |last2= Barnes |first2=R.C.M. |last3=Stephen |first3=J.H. |last4=Howells |first4=G.A.}}</ref> Problems with the reliability of early batches of point contact and alloyed junction transistors meant that the machine's [[mean time between failures]] was about 90&nbsp;minutes, but this improved once the more reliable [[bipolar junction transistor]]s became available.{{sfn|Lavington|1998|pp=36–37}}
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From 1975 to 1977, most microcomputers, such as the [[KIM-1|MOS Technology KIM-1]], the [[Altair 8800]], and some versions of the [[Apple I]], were sold as kits for do-it-yourselfers. Pre-assembled systems did not gain much ground until 1977, with the introduction of the [[Apple II]], the Tandy [[TRS-80]], the first [[SWTPC]] computers, and the [[Commodore PET]]. Computing has evolved with microcomputer architectures, with features added from their larger brethren, now dominant in most market segments.
 
A NeXT Computer and its [[Object-oriented programming|object-oriented]] development tools and libraries were used by [[Tim Berners-Lee]] and [[Robert Cailliau]] at [[CERN]] to develop the world's first [[web server]] software, [[CERN httpd]], and also used to write the first [[web browser]], [[WorldWideWeb]].
 
Systems as complicated as computers require very high [[reliability engineering|reliability]]. ENIAC remained on, in continuous operation from 1947 to 1955, for eight years before being shut down. Although a vacuum tube might fail, it would be replaced without bringing down the system. By the simple strategy of never shutting down ENIAC, the failures were dramatically reduced. The vacuum-tube [[Semi-Automatic Ground Environment|SAGE]] air-defense computers became remarkably reliable – installed in pairs, one off-line, tubes likely to fail did so when the computer was intentionally run at reduced power to find them. [[Hot plugging|Hot-pluggable]] hard disks, like the hot-pluggable vacuum tubes of yesteryear, continue the tradition of repair during continuous operation. Semiconductor memories routinely have no errors when they operate, although operating systems like Unix have employed memory tests on start-up to detect failing hardware. Today, the requirement of reliable performance is made even more stringent when [[server farm]]s are the delivery platform.<ref>{{cite web |last=Shankland |first=Stephen |title=Google uncloaks once-secret server |website=CNET |date=1 April 2009 |url=https://news.cnet.com/8301-1001_3-10209580-92.html |access-date=2009-04-01 |url-status=dead |archive-url=https://web.archive.org/web/20140716084210/http://www.cnet.com/news/google-uncloaks-once-secret-server-10209580/ |archive-date=2014-07-16}} "Since 2005, its [Google's] data centers have been composed of standard shipping containers—each with 1,160 servers and a power consumption that can reach 250 kilowatts." —Ben Jai of Google.</ref> Google has managed this by using fault-tolerant software to recover from hardware failures, and is even working on the concept of replacing entire server farms on-the-fly, during a service event.<ref>{{cite web |last=Shankland |first=Stephen |title=Google spotlights data center inner workings |website=CNET |date=30 May 2008 |url=https://news.cnet.com/8301-10784_3-9955184-7.html?tag=nefd.lede |access-date=2008-05-31 |url-status=dead |archive-url=https://web.archive.org/web/20140818092344/http://www.cnet.com/news/google-spotlights-data-center-inner-workings/ |archive-date=2014-08-18}} "If you're running 10,000 machines, something is going to die every day." —Jeff Dean of Google.</ref><ref>{{cite web|title=Google Groups |url=https://groups.google.com/group/google-appengine/browse_thread/thread/a7640a2743922dcf?pli=1 |access-date=11 August 2015 |archive-url=https://web.archive.org/web/20110913014648/https://groups.google.com/group/google-appengine/browse_thread/thread/a7640a2743922dcf?pli=1 |archive-date=2011-09-13|url-status=live}}</ref>
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* [[History of personal computers]]
* [[History of software]]
* {{Annotated link|History of supercomputing}}
* [[Information Age]]
* [[IT History Society]]