Editing Central processing unit (section)

==History==
{{Main|History of general-purpose CPUs}}
[[File:Edvac.jpg|thumb|[[EDVAC]], one of the first stored-program computers]]

Early computers such as the [[ENIAC]] had to be physically rewired to perform different tasks, which caused these machines to be called "fixed-program computers".<ref>{{cite book|last1=Regan|first1=Gerard|title=A Brief History of Computing|isbn=978-1848000834|page=66|url=https://books.google.com/books?isbn=1848000839|access-date=26 November 2014|year=2008|publisher=Springer }}</ref> The "central processing unit" term has been in use since as early as 1955.<ref name= weik1955>{{cite web| last = Weik | first = Martin H. | title = A Survey of Domestic Electronic Digital Computing Systems | publisher = [[Ballistic Research Laboratory]] | url = http://ed-thelen.org/comp-hist/BRL-i.html#IBM-CPC | year = 1955 | access-date = 2020-11-15 | archive-date = 2021-01-26 | archive-url = https://web.archive.org/web/20210126045809/http://ed-thelen.org/comp-hist/BRL-i.html#IBM-CPC | url-status = live }}</ref><ref name="weik1961">{{cite journal | last = Weik | first = Martin H. | title = A Third Survey of Domestic Electronic Digital Computing Systems | publisher = [[Ballistic Research Laboratory]] | url = http://ed-thelen.org/comp-hist/BRL61.html | year = 1961 | access-date = 2005-12-16 | archive-date = 2017-09-11 | archive-url = https://web.archive.org/web/20170911041654/http://ed-thelen.org/comp-hist/BRL61.html | url-status = live |website=Ed Thelen's Nike Missile Web Site }}</ref> Since the term "CPU" is generally defined as a device for [[software]] (computer program) execution, the earliest devices that could rightly be called CPUs came with the advent of the [[stored-program computer]].

The idea of a stored-program computer had already been present in the design of [[J. Presper Eckert|John Presper Eckert]] and [[John William Mauchly]]'s [[ENIAC]], but was initially omitted so that it could be finished sooner.<ref>{{cite web|title=Bit By Bit|url=http://ds.haverford.edu/bitbybit/bit-by-bit-contents/chapter-five/5-1-stored-program-computing/|archive-url=https://web.archive.org/web/20121013210908/http://ds.haverford.edu/bitbybit/bit-by-bit-contents/chapter-five/5-1-stored-program-computing/|publisher=Haverford College|access-date=August 1, 2015|archive-date=October 13, 2012|url-status=dead}}</ref> On June 30, 1945, before ENIAC was made, mathematician [[John von Neumann]] distributed a paper entitled ''[[First Draft of a Report on the EDVAC]]''. It was the outline of a stored-program computer that would eventually be completed in August 1949.<ref>{{cite tech report | title = First Draft of a Report on the EDVAC | publisher = [[Moore School of Electrical Engineering]], [[University of Pennsylvania]] | url = https://www.wiley.com/legacy/wileychi/wang_archi/supp/appendix_a.pdf | year = 1945 | access-date = 2018-03-31 | archive-date = 2021-03-09 | archive-url = https://web.archive.org/web/20210309062704/https://www.wiley.com/legacy/wileychi/wang_archi/supp/appendix_a.pdf | url-status = live }}</ref> [[EDVAC]] was designed to perform a certain number of instructions (or operations) of various types. Significantly, the programs written for EDVAC were to be stored in high-speed [[Memory (computers)|computer memory]] rather than specified by the physical wiring of the computer.<ref>{{cite encyclopedia|title=The Modern History of Computing|url=https://plato.stanford.edu/entries/computing-history/|author=Stanford University|encyclopedia=The Stanford Encyclopedia of Philosophy|access-date=September 25, 2015}}</ref> This overcame a severe limitation of ENIAC, which was the considerable time and effort required to reconfigure the computer to perform a new task.<ref>{{cite web |title=ENIAC's Birthday |url=https://mitpress.mit.edu/blog/eniacs-birthday |publisher=The MIT Press |access-date=October 17, 2018 |date=February 9, 2016 |archive-date=October 17, 2018 |archive-url=https://web.archive.org/web/20181017163347/https://mitpress.mit.edu/blog/eniacs-birthday |url-status=dead }}</ref> With von Neumann's design, the program that EDVAC ran could be changed simply by changing the contents of the memory. EDVAC was not the first stored-program computer; the [[Manchester Baby]], which was a small-scale experimental stored-program computer, ran its first program on 21 June 1948<ref>{{citation |last=Enticknap |first=Nicholas |title=Computing's Golden Jubilee |journal=Resurrection |issue=20 |publisher=The Computer Conservation Society |date=Summer 1998 |url=http://www.computerconservationsociety.org/resurrection/res20.htm#d |issn=0958-7403 |access-date=26 June 2019 |archive-date=17 March 2019 |archive-url=https://web.archive.org/web/20190317222331/http://www.computerconservationsociety.org/resurrection/res20.htm#d |url-status=live }}</ref> and the [[Manchester Mark 1]] ran its first program during the night of 16–17 June 1949.<ref>{{cite web|title=The Manchester Mark 1|url=http://curation.cs.manchester.ac.uk/digital60/www.digital60.org/birth/manchestercomputers/mark1/manchester.html|work=The University of Manchester|access-date=September 25, 2015|archive-date=January 25, 2015|archive-url=https://web.archive.org/web/20150125141909/http://curation.cs.manchester.ac.uk/digital60/www.digital60.org/birth/manchestercomputers/mark1/manchester.html|url-status=live}}</ref>

Early CPUs were custom designs used as part of a larger and sometimes distinctive computer.<ref>{{cite web|title=The First Generation|url=http://www.computerhistory.org/revolution/birth-of-the-computer/4/92|publisher=Computer History Museum|access-date=September 29, 2015|archive-date=November 22, 2016|archive-url=https://web.archive.org/web/20161122064835/http://www.computerhistory.org/revolution/birth-of-the-computer/4/92|url-status=live}}</ref> However, this method of designing custom CPUs for a particular application has largely given way to the development of multi-purpose processors produced in large quantities. This standardization began in the era of discrete [[transistor]] [[Mainframe computer|mainframes]] and [[minicomputer]]s, and has rapidly accelerated with the popularization of the [[integrated circuit]] (IC). The IC has allowed increasingly complex CPUs to be designed and manufactured to tolerances on the order of [[Nanometre|nanometers]].<ref name="nobel">{{cite web|title=The History of the Integrated Circuit|url=https://educationalgames.nobelprize.org/educational/physics/integrated_circuit/history/index.html|website=Nobelprize.org|access-date=July 17, 2022|archive-date=May 22, 2022|archive-url=https://web.archive.org/web/20220522104138/https://educationalgames.nobelprize.org/educational/physics/integrated_circuit/history/index.html|url-status=live}}</ref> Both the miniaturization and standardization of CPUs have increased the presence of digital devices in modern life far beyond the limited application of dedicated computing machines. Modern microprocessors appear in electronic devices ranging from automobiles<ref>{{cite web|last1=Turley|first1=Jim|title=Motoring with microprocessors|date=11 August 2003|url=https://www.embedded.com/motoring-with-microprocessors/|publisher=Embedded|access-date=December 26, 2022|archive-date=14 October 2022|archive-url=https://web.archive.org/web/20221014214157/https://www.embedded.com/motoring-with-microprocessors/|url-status=live}}</ref> to cellphones,<ref>{{cite web|title=Mobile Processor Guide – Summer 2013|url=http://www.androidauthority.com/mobile-processor-guide-summer-2013-234354/|publisher=Android Authority|access-date=November 15, 2015|date=2013-06-25|archive-date=2015-11-17|archive-url=https://web.archive.org/web/20151117034027/http://www.androidauthority.com/mobile-processor-guide-summer-2013-234354/|url-status=live}}</ref> and sometimes even in toys.<ref>{{cite web |title=Section 250: Microprocessors and Toys: An Introduction to Computing Systems |url=https://eng100.engin.umich.edu/list/sec250/ |publisher=The University of Michigan |access-date=October 9, 2018 |archive-date=April 13, 2021 |archive-url=https://web.archive.org/web/20210413194655/https://eng100.engin.umich.edu/list/sec250/ |url-status=dead }}</ref><ref>{{cite web|title=ARM946 Processor |url=https://www.arm.com/products/processors/classic/arm9/arm946.php|publisher=ARM|url-status=dead|archive-url = https://web.archive.org/web/20151117015143/https://www.arm.com/products/processors/classic/arm9/arm946.php|archive-date = 17 November 2015}}</ref>

While von Neumann is most often credited with the design of the stored-program computer because of his design of EDVAC, and the design became known as the [[von Neumann architecture]], others before him, such as [[Konrad Zuse]], had suggested and implemented similar ideas.<ref>{{cite web|title=Konrad Zuse|url=http://www.computerhistory.org/fellowawards/hall/konrad-zuse/|publisher=Computer History Museum|access-date=September 29, 2015|archive-date=October 3, 2016|archive-url=https://web.archive.org/web/20161003015151/http://www.computerhistory.org/fellowawards/hall/konrad-zuse|url-status=live}}</ref> The so-called [[Harvard architecture]] of the [[Harvard Mark I]], which was completed before EDVAC,<ref>{{cite web|title=Timeline of Computer History: Computers|url=https://www.computerhistory.org/timeline/computers/|publisher=Computer History Museum|access-date=November 21, 2015|archive-date=December 29, 2017|archive-url=https://web.archive.org/web/20171229052342/http://www.computerhistory.org/timeline/computers/|url-status=live}}</ref><ref>{{cite web |last=White |first=Stephen |title=A Brief History of Computing – First Generation Computers |url=http://trillian.randomstuff.org.uk/~stephen/history/timeline-GEN1.html |url-status=live |archive-url=https://web.archive.org/web/20180102205958/http://trillian.randomstuff.org.uk/~stephen/history/timeline-GEN1.html |archive-date=January 2, 2018 |access-date=November 21, 2015}}</ref> also used a stored-program design using [[Punched tape|punched paper tape]] rather than electronic memory.<ref>{{cite web |title=Harvard University Mark I Paper Tape Punch Unit |url=https://www.computerhistory.org/collections/catalog/102698407 |url-status=live |archive-url=https://web.archive.org/web/20151122011934/http://www.computerhistory.org/collections/catalog/102698407 |archive-date=November 22, 2015 |access-date=November 21, 2015 |publisher=Computer History Museum}}</ref> The key difference between the von Neumann and Harvard architectures is that the latter separates the storage and treatment of CPU instructions and data, while the former uses the same memory space for both.<ref>{{cite web|title=What is the difference between a von Neumann architecture and a Harvard architecture?|url=http://infocenter.arm.com/help/index.jsp?topic=%2Fcom.arm.doc.faqs%2F3738.html|publisher=ARM|access-date=November 22, 2015|archive-date=November 18, 2015|archive-url=https://web.archive.org/web/20151118200529/http://infocenter.arm.com/help/index.jsp?topic=%2Fcom.arm.doc.faqs%2F3738.html|url-status=live}}</ref> Most modern CPUs are primarily von Neumann in design, but CPUs with the Harvard architecture are seen as well, especially in embedded applications; for instance, the [[Atmel AVR]] microcontrollers are Harvard-architecture processors.<ref>{{cite web|title=Advanced Architecture Optimizes the Atmel AVR CPU|url=http://www.atmel.com/technologies/cpu_core/avr.aspx|publisher=Atmel|access-date=November 22, 2015|archive-date=November 14, 2015|archive-url=https://web.archive.org/web/20151114090428/http://www.atmel.com/technologies/cpu_core/avr.aspx|url-status=dead}}</ref>

[[Relay]]s and [[vacuum tube]]s (thermionic tubes) were commonly used as switching elements;<ref>{{cite web|title=Switches, transistors and relays|url=http://www.bbc.co.uk/schools/gcsebitesize/design/electronics/switchesrev5.shtml|publisher=BBC |url-status=dead|archive-url = https://web.archive.org/web/20161205142752/http://www.bbc.co.uk/schools/gcsebitesize/design/electronics/switchesrev5.shtml|archive-date = 5 December 2016}}</ref><ref>{{cite web|title=Introducing the Vacuum Transistor: A Device Made of Nothing|url=https://spectrum.ieee.org/introducing-the-vacuum-transistor-a-device-made-of-nothing|website=IEEE Spectrum|access-date=27 January 2019|date=2014-06-23|archive-date=2018-03-23|archive-url=https://web.archive.org/web/20180323183612/https://spectrum.ieee.org/semiconductors/devices/introducing-the-vacuum-transistor-a-device-made-of-nothing|url-status=live}}</ref> a useful computer requires thousands or tens of thousands of switching devices. The overall speed of a system is dependent on the speed of the switches. [[Vacuum-tube computer]]s such as EDVAC tended to average eight hours between failures, whereas relay computers—such as the slower but earlier [[Harvard Mark I]]—failed very rarely.<ref name="weik1961" /> In the end, tube-based CPUs became dominant because the significant speed advantages afforded generally outweighed the reliability problems. Most of these early synchronous CPUs ran at low [[clock rate]]s compared to modern microelectronic designs. Clock signal frequencies ranging from 100 [[Hertz|kHz]] to 4&nbsp;MHz were very common at this time, limited largely by the speed of the switching devices they were built with.<ref>{{cite book|title=What Is Computer Performance?|url=http://www.nap.edu/read/12980/chapter/5#55|publisher=The National Academies Press|access-date=May 16, 2016|doi=10.17226/12980|year=2011|isbn=978-0-309-15951-7|archive-date=June 5, 2016|archive-url=https://web.archive.org/web/20160605083842/http://www.nap.edu/read/12980/chapter/5#55|url-status=live}}</ref>

===Transistor CPUs===
[[File:IBM PPC604e 200.jpg|thumb|IBM PowerPC 604e processor]]
{{Main|Transistor computer}}
The design complexity of CPUs increased as various technologies facilitated the building of smaller and more reliable electronic devices. The first such improvement came with the advent of the [[transistor]]. Transistorized CPUs during the 1950s and 1960s no longer had to be built out of bulky, unreliable, and fragile switching elements, like [[vacuum tube]]s and [[relay]]s.<ref>{{cite web|title=1953: Transistorized Computers Emerge|url=http://www.computerhistory.org/siliconengine/transistorized-computers-emerge/|work=Computer History Museum|access-date=June 3, 2016|archive-date=June 1, 2016|archive-url=https://web.archive.org/web/20160601191253/http://www.computerhistory.org/siliconengine/transistorized-computers-emerge/|url-status=live}}</ref> With this improvement, more complex and reliable CPUs were built onto one or several [[printed circuit board]]s containing discrete (individual) components.

In 1964, [[IBM]] introduced its [[IBM System/360]] computer architecture that was used in a series of computers capable of running the same programs with different speeds and performances.<ref>{{cite web|url=http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_FS360.html|title=IBM System/360 Dates and Characteristics|publisher=IBM|date=2003-01-23|access-date=2016-01-13|archive-date=2017-11-21|archive-url=https://web.archive.org/web/20171121223500/http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_FS360.html|url-status=dead}}</ref> This was significant at a time when most electronic computers were incompatible with one another, even those made by the same manufacturer. To facilitate this improvement, IBM used the concept of a [[microprogram]] (often called "microcode"), which still sees widespread use in modern CPUs.<ref name="amdahl1964">{{cite journal | last1 = Amdahl | first1 = G. M. | author-link1 = Gene Amdahl | last2 = Blaauw | first2 = G. A. | author-link2 = Gerrit Blaauw | last3 = Brooks | first3 = F. P. Jr. | author-link3 = Fred Brooks | title = Architecture of the IBM System/360 | journal = IBM Journal of Research and Development | volume = 8 | issue = 2 | pages = 87–101 | issn = 0018-8646 | publisher = [[IBM]] | date = April 1964 | doi = 10.1147/rd.82.0087 }}</ref> The System/360 architecture was so popular that it dominated the [[mainframe computer]] market for decades and left a legacy that is continued by similar modern computers like the IBM [[IBM System z|zSeries]].<ref>{{cite web|last1=Brodkin|first1=John|title=50 years ago, IBM created mainframe that helped send men to the Moon|url=https://arstechnica.com/information-technology/2014/04/50-years-ago-ibm-created-mainframe-that-helped-bring-men-to-the-moon/|website=Ars Technica|date=7 April 2014|access-date=9 April 2016|archive-date=8 April 2016|archive-url=https://web.archive.org/web/20160408105602/http://arstechnica.com/information-technology/2014/04/50-years-ago-ibm-created-mainframe-that-helped-bring-men-to-the-moon/|url-status=live}}</ref><ref>{{cite web|last1=Clarke|first1=Gavin|title=Why won't you DIE? IBM's S/360 and its legacy at 50|url=https://www.theregister.co.uk/2014/04/07/ibm_s_360_50_anniversary/|website=The Register|access-date=9 April 2016|archive-date=24 April 2016|archive-url=https://web.archive.org/web/20160424121559/http://www.theregister.co.uk/2014/04/07/ibm_s_360_50_anniversary/|url-status=live}}</ref> In 1965, [[Digital Equipment Corporation]] (DEC) introduced another influential computer aimed at the scientific and research markets—the [[PDP-8]].<ref>{{cite web|title=Online PDP-8 Home Page, Run a PDP-8|url=http://www.pdp8.net/index.shtml|website=PDP8|access-date=September 25, 2015|archive-date=August 11, 2015|archive-url=https://web.archive.org/web/20150811174442/http://www.pdp8.net/index.shtml|url-status=live}}</ref>
[[File:Board with SPARC64 VIIIfx processors on display in Fujitsu HQ.JPG|thumb|Fujitsu board with SPARC64 VIIIfx processors]]
Transistor-based computers had several distinct advantages over their predecessors. Aside from facilitating increased reliability and lower power consumption, transistors also allowed CPUs to operate at much higher speeds because of the short switching time of a transistor in comparison to a tube or relay.<ref>{{cite web|title=Transistors, Relays, and Controlling High-Current Loads|url=https://itp.nyu.edu/physcomp/lessons/electronics/transistors-relays-and-controlling-high-current-loads/|publisher=ITP Physical Computing|work=New York University|access-date=9 April 2016|archive-date=21 April 2016|archive-url=https://web.archive.org/web/20160421232136/https://itp.nyu.edu/physcomp/lessons/electronics/transistors-relays-and-controlling-high-current-loads/|url-status=live}}</ref> The increased reliability and dramatically increased speed of the switching elements, which were almost exclusively transistors by this time; CPU clock rates in the tens of megahertz were easily obtained during this period.<ref name = pcgamer>{{cite magazine|last1=Lilly|first1=Paul|title=A Brief History of CPUs: 31 Awesome Years of x86|url=http://www.pcgamer.com/a-brief-history-of-cpus-31-awesome-years-of-x86/|magazine=PC Gamer|access-date=June 15, 2016|date=2009-04-14|archive-date=2016-06-13|archive-url=https://web.archive.org/web/20160613202439/http://www.pcgamer.com/a-brief-history-of-cpus-31-awesome-years-of-x86/|url-status=live}}</ref> Additionally, while discrete transistor and IC CPUs were in heavy usage, new high-performance designs like [[single instruction, multiple data]] (SIMD) [[vector processor]]s began to appear.<ref name="patterson">{{cite book |last1=Patterson |first1=David A. |url=https://archive.org/details/computerorganiz000henn/page/751 |title=Computer Organization and Design: the Hardware/Software Interface |last2=Hennessy |first2=John L. |last3=Larus |first3=James R. |date=1999 |publisher=Kaufmann |isbn=978-1558604285 |edition=3rd printing of 2nd |location=San Francisco, California |page=[https://archive.org/details/computerorganiz000henn/page/751 751] |language=en-us}}</ref> These early experimental designs later gave rise to the era of specialized [[supercomputer]]s like those made by [[Cray|Cray Inc]] and [[Fujitsu|Fujitsu Ltd]].<ref name="patterson"/>

===Small-scale integration CPUs===
[[File:PDP-8i cpu.jpg|thumb|CPU, [[magnetic-core memory|core memory]] and [[external bus]] interface of a DEC [[PDP-8]]/I, made of medium-scale integrated circuits]]

During this period, a method of manufacturing many interconnected transistors in a compact space was developed. The [[integrated circuit]] (IC) allowed a large number of transistors to be manufactured on a single [[semiconductor]]-based [[Die (integrated circuit)|die]], or "chip". At first, only very basic non-specialized digital circuits such as [[NOR gate]]s were miniaturized into ICs.<ref>{{cite web |title=1962: Aerospace systems are first the applications for ICs in computers |url=http://www.computerhistory.org/siliconengine/aerospace-systems-are-first-the-applications-for-ics-in-computers/ |publisher=[[Computer History Museum]] |access-date=October 9, 2018 |archive-date=October 5, 2018 |archive-url=https://web.archive.org/web/20181005083606/http://www.computerhistory.org/siliconengine/aerospace-systems-are-first-the-applications-for-ics-in-computers/ |url-status=live }}</ref> CPUs based on these "building block" ICs are generally referred to as "small-scale integration" (SSI) devices. SSI ICs, such as the ones used in the [[Apollo Guidance Computer]], usually contained up to a few dozen transistors. To build an entire CPU out of SSI ICs required thousands of individual chips, but still consumed much less space and power than earlier discrete transistor designs.<ref>{{cite web |title=The integrated circuits in the Apollo manned lunar landing program |url=https://www.hq.nasa.gov/alsj/ic-pg3.html |publisher=National Aeronautics and Space Administration |access-date=October 9, 2018 |archive-date=July 21, 2019 |archive-url=https://web.archive.org/web/20190721173218/https://www.hq.nasa.gov/alsj/ic-pg3.html |url-status=live }}</ref>

IBM's [[System/370]], follow-on to the System/360, used SSI ICs rather than [[Solid Logic Technology]] discrete-transistor modules.<ref>{{cite web|title=System/370 Announcement|url=http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PR370.html|website=IBM Archives|access-date=October 25, 2017|date=2003-01-23|archive-date=2018-08-20|archive-url=https://web.archive.org/web/20180820122836/https://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PR370.html|url-status=dead}}</ref><ref>{{cite web|title=System/370 Model 155 (Continued)|url=https://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3155B.html|website=IBM Archives|access-date=October 25, 2017|date=2003-01-23|archive-date=2016-07-20|archive-url=https://web.archive.org/web/20160720234350/http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3155B.html|url-status=dead}}</ref> DEC's [[PDP-8]]/I and KI10 [[PDP-10]] also switched from the individual transistors used by the PDP-8 and KA PDP-10 to SSI ICs,<ref>{{cite web|url=http://homepage.divms.uiowa.edu/~jones/pdp8/models/|title=Models and Options|publisher=The Digital Equipment Corporation PDP-8|access-date=June 15, 2018|archive-date=June 26, 2018|archive-url=https://web.archive.org/web/20180626145311/http://homepage.divms.uiowa.edu/~jones/pdp8/models/|url-status=live}}</ref> and their extremely popular [[PDP-11]] line was originally built with SSI ICs, but was eventually implemented with LSI components once these became practical.

===Large-scale integration CPUs===
[[Lee Boysel]] published influential articles, including a 1967 "manifesto", which described how to build the equivalent of a 32-bit mainframe computer from a relatively small number of [[large-scale integration]] circuits (LSI).<ref>{{cite book |author=Bassett |first=Ross Knox |url=https://books.google.com/books?id=UUbB3d2UnaAC |title=To the Digital Age: Research Labs, Start-up Companies, and the Rise of MOS Technology |publisher=[[The Johns Hopkins University Press]] |year=2007 |isbn=978-0-8018-6809-2 |pages=127–128, 256, and 314 |language=en-us}}</ref><ref name="shirriff">{{cite web |first=Ken |last=Shirriff
|url=http://www.righto.com/2015/05/the-texas-instruments-tmx-1795-first.html |title=The Texas Instruments TMX 1795: the first, forgotten microprocessor |archive-url=https://web.archive.org/web/20210126074942/http://www.righto.com/2015/05/the-texas-instruments-tmx-1795-first.html |archive-date=2021-01-26 |url-status=live}}</ref> The only way to build LSI chips, which are chips with a hundred or more gates, was to build them using a [[MOSFET|metal–oxide–semiconductor]] (MOS) [[semiconductor manufacturing process]] (either [[PMOS logic]], [[NMOS logic]], or [[CMOS]] logic). However, some companies continued to build processors out of bipolar [[transistor–transistor logic]] (TTL) chips because bipolar junction transistors were faster than MOS chips up until the 1970s (a few companies such as [[Datapoint]] continued to build processors out of TTL chips until the early 1980s).<ref name="shirriff" /> In the 1960s, MOS ICs were slower and initially considered useful only in applications that required low power.<ref>{{cite web|url=http://www.brown.edu/Departments/Engineering/Labs/ddzo/speed.html|title=Speed & Power in Logic Families|access-date=2017-08-02|archive-date=2017-07-26|archive-url=https://web.archive.org/web/20170726175011/http://www.brown.edu/Departments/Engineering/Labs/ddzo/speed.html|url-status=live}}.</ref><ref>{{cite book |first=T. J. |last=Stonham |url=https://books.google.com/books?id=UE6vFEnGP2kC |title=Digital Logic Techniques: Principles and Practice |date=1996 |page=174|publisher=Taylor & Francis |isbn=9780412549700 }}</ref> Following the development of [[silicon-gate]] MOS technology by [[Federico Faggin]] at Fairchild Semiconductor in 1968, MOS ICs largely replaced bipolar TTL as the standard chip technology in the late 1970s.<ref>{{cite web |title=1968: Silicon Gate Technology Developed for ICs |url=https://www.computerhistory.org/siliconengine/silicon-gate-technology-developed-for-ics/ |website=Computer History Museum |access-date=2019-08-16 |archive-date=2020-07-29 |archive-url=https://web.archive.org/web/20200729145834/https://www.computerhistory.org/siliconengine/silicon-gate-technology-developed-for-ics/ |url-status=live }}</ref>

As the [[microelectronic]] technology advanced, an increasing number of transistors were placed on ICs, decreasing the number of individual ICs needed for a complete CPU. MSI and LSI ICs increased transistor counts to hundreds, and then thousands. By 1968, the number of ICs required to build a complete CPU had been reduced to 24 ICs of eight different types, with each IC containing roughly 1000 MOSFETs.<ref>{{cite conference |first=R. K. |last=Booher |url=http://www.computer.org/csdl/proceedings/afips/1968/5072/00/50720877.pdf |title=MOS GP Computer |publisher=[[AFIPS]] |page=877 |date=1968 |conference=International Workshop on Managing Requirements Knowledge
|doi=10.1109/AFIPS.1968.126 |archive-url=https://web.archive.org/web/20170714014430/https://www.computer.org/csdl/proceedings/afips/1968/5072/00/50720877.pdf |archive-date=2017-07-14 |url-status=live}}</ref> In stark contrast with its SSI and MSI predecessors, the first LSI implementation of the PDP-11 contained a CPU composed of only four LSI integrated circuits.<ref>{{cite book |title=LSI-11, PDP-11/03 user's manual |date=November 1975 |publisher=[[Digital Equipment Corporation]] |edition=2nd |location=Maynard, Massachusetts |page=4{{hyp}}3 |language=en-us |chapter=LSI-11 Module Descriptions |access-date=2015-02-20 |url=http://www.bitsavers.org/pdf/dec/pdp11/1103/EK-LSI11-TM-002.pdf |archive-url=https://web.archive.org/web/20211010023115/http://www.bitsavers.org/pdf/dec/pdp11/1103/EK-LSI11-TM-002.pdf |archive-date=2021-10-10 |url-status=live}}</ref>

===Microprocessors===
{{main|Microprocessor}}
{{multiple image
|width = 220
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|image1 = 80486dx2-large.jpg
|caption1 = [[Die (integrated circuit)|Die]] of an [[Intel 80486DX2]] microprocessor (actual size: 12 × 6.75&nbsp;mm) in its packaging
|image2 = EBIntel Corei5.JPG
|caption2 = [[Intel]] Core i5 CPU on a [[Sony Vaio E series|Vaio E series]] laptop motherboard (on the right, beneath the [[heat pipe]])
}}
[[File:Laptop-intel-core2duo-t5500.jpg|thumb|Inside of a laptop, with the CPU removed from socket]]
Since microprocessors were first introduced they have almost completely overtaken all other central processing unit implementation methods. The first commercially available microprocessor, made in 1971, was the [[Intel 4004]], and the first widely used microprocessor, made in 1974, was the [[Intel 8080]]. Mainframe and minicomputer manufacturers of the time launched proprietary IC development programs to upgrade their older [[computer architecture]]s, and eventually produced [[instruction set architecture|instruction set]] compatible microprocessors that were backward-compatible with their older hardware and software. Combined with the advent and eventual success of the ubiquitous [[personal computer]], the term ''CPU'' is now applied almost exclusively{{Efn|Integrated circuits are now used to implement all CPUs, except for a few machines designed to withstand large electromagnetic pulses, say from a nuclear weapon.}} to microprocessors. Several CPUs (denoted ''cores'') can be combined in a single processing chip.<ref>{{cite web |url=https://www.techtarget.com/searchdatacenter/definition/multi-core-processor |publisher=TechTarget |title=What is a multicore processor and how does it work? |first=Stephen J. |last=Bigelow |date=March 2022 |access-date=July 17, 2022 |archive-date=July 11, 2022 |archive-url=https://web.archive.org/web/20220711210214/https://www.techtarget.com/searchdatacenter/definition/multi-core-processor |url-status=live }}</ref>

{{anchor|DISCRETE-PROCESSOR}}
Previous generations of CPUs were implemented as [[discrete components]] and numerous small [[integrated circuit]]s (ICs) on one or more circuit boards.<ref>{{cite web |author=Birkby |first=Richard |title=A Brief History of the Microprocessor |url=http://www.computermuseum.li/Testpage/MicroprocessorHistory.htm |url-status=dead |archive-url=https://web.archive.org/web/20150923205820/http://www.computermuseum.li/Testpage/MicroprocessorHistory.htm |archive-date=September 23, 2015 |access-date=October 13, 2015 |website=computermuseum.li}}</ref> Microprocessors, on the other hand, are CPUs manufactured on a very small number of ICs; usually just one.<ref name=Osborne80>{{cite book | first=Adam | last=Osborne | title=An Introduction to Microcomputers | volume=1: Basic Concepts | edition=2nd | publisher=Osborne-McGraw Hill | location=Berkeley, California | year=1980 | isbn=978-0-931988-34-9 | url=https://archive.org/details/introductiontomi00adam }}</ref> The overall smaller CPU size, as a result of being implemented on a single die, means faster switching time because of physical factors like decreased gate [[parasitic capacitance]].<ref>{{cite web|last1=Zhislina|first1=Victoria|title=Why has CPU frequency ceased to grow?|url=https://software.intel.com/en-us/blogs/2014/02/19/why-has-cpu-frequency-ceased-to-grow|publisher=Intel|access-date=October 14, 2015|date=2014-02-19|archive-date=2017-06-21|archive-url=https://web.archive.org/web/20170621074555/https://software.intel.com/en-us/blogs/2014/02/19/why-has-cpu-frequency-ceased-to-grow|url-status=live}}</ref><ref>{{cite web |title=MOS Transistor – Electrical Engineering & Computer Science |url=http://www.eecs.berkeley.edu/~tking/theses/bsriram.pdf |url-status=live |archive-url=https://ghostarchive.org/archive/20221009/http://www.eecs.berkeley.edu/~tking/theses/bsriram.pdf |archive-date=2022-10-09 |access-date=October 14, 2015 |publisher=University of California}}</ref> This has allowed synchronous microprocessors to have clock rates ranging from tens of megahertz to several gigahertz. Additionally, the ability to construct exceedingly small transistors on an IC has increased the complexity and number of transistors in a single CPU many fold. This widely observed trend is described by [[Moore's law]], which had proven to be a fairly accurate predictor of the growth of CPU (and other IC) complexity until 2016.<ref>{{Cite news|url=https://www.technologyreview.com/s/601441/moores-law-is-dead-now-what/|title=Moore's Law Is Dead. Now What?|last=Simonite|first=Tom|work=MIT Technology Review|access-date=2018-08-24|language=en|archive-date=2018-08-22|archive-url=https://web.archive.org/web/20180822071655/https://www.technologyreview.com/s/601441/moores-law-is-dead-now-what/|url-status=live}}</ref><ref name="MooresLaw">{{cite interview|title=Excerpts from A Conversation with Gordon Moore: Moore's Law |first=Gordon |last=Moore |author-link=Gordon Moore |publisher=Intel |year=2005 |url=http://download.intel.com/museum/Moores_Law/Video-Transcripts/Excepts_A_Conversation_with_Gordon_Moore.pdf |access-date=2012-07-25 |url-status=dead |archive-url=https://web.archive.org/web/20121029060050/http://download.intel.com/museum/Moores_Law/Video-Transcripts/Excepts_A_Conversation_with_Gordon_Moore.pdf |archive-date=2012-10-29 }}</ref>

While the complexity, size, construction and general form of CPUs have changed enormously since 1950,<ref>{{cite web|title=A detailed history of the processor|url=https://www.techjunkie.com/a-cpu-history/|publisher=Tech Junkie|date=15 December 2016|access-date=14 August 2019|archive-date=14 August 2019|archive-url=https://web.archive.org/web/20190814125742/https://www.techjunkie.com/a-cpu-history/|url-status=live}}</ref> the basic design and function has not changed much at all. Almost all common CPUs today can be very accurately described as von Neumann stored-program machines.<ref>{{cite book |chapter=Von Neumann Computers | first1=Rudolf|last1= Eigenmann |first2= David|last2=Lilja|title=Wiley Encyclopedia of Electrical and Electronics Engineering |s2cid=8197337 |year=1998 |doi=10.1002/047134608X.W1704 |isbn=047134608X }}</ref>{{Efn|The so-called "von Neumann" memo expounded the idea of stored programs,<ref>{{cite magazine|last1=Aspray|first1=William|title=The stored program concept |doi=10.1109/6.58457|magazine=IEEE Spectrum|volume=27|issue=9|date=September 1990|page=51 }}</ref> which for example may be stored on [[punched card]]s, paper tape, or magnetic tape.}} As Moore's law no longer holds, concerns have arisen about the limits of integrated circuit transistor technology. Extreme miniaturization of [[logic gate|electronic gates]] is causing the effects of phenomena like [[electromigration]] and [[subthreshold leakage]] to become much more significant.<ref>{{cite web |last1= Saraswat |first1=Krishna |title=Trends in Integrated Circuits Technology |url=https://web.stanford.edu/class/ee311/NOTES/TrendsSlides.pdf |archive-url=https://web.archive.org/web/20150724091731/https://web.stanford.edu/class/ee311/NOTES/TrendsSlides.pdf |archive-date=2015-07-24 |url-status=dead|access-date=June 15, 2018}}</ref><ref>{{cite web |title=Electromigration |url=http://www.csl.mete.metu.edu.tr/Electromigration/emig.htm |publisher=Middle East Technical University |access-date=June 15, 2018 |archive-date=July 31, 2017 |archive-url=https://web.archive.org/web/20170731070649/http://www.csl.mete.metu.edu.tr/Electromigration/emig.htm |url-status=live }}</ref> These newer concerns are among the many factors causing researchers to investigate new methods of computing such as the [[quantum computer]], as well as to expand the use of [[Parallel computing|parallelism]] and other methods that extend the usefulness of the classical von Neumann model.