Central processing unit: Difference between revisions

{{Redirect|CPU}}

[[File:Intel Xeon 3060 Conroe (Reshoot) - Flickr - cole8888.jpg|thumb|280px|upright=1.5|Inside a central processing unit: The [[integrated circuit]] of Intel's [[List of Intel Xeon processors (Core-based)#ark27205|Xeon 3060]], first manufactured in 2006]]

==History==

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>

===Transistor CPUs===

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.

[[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"/>

===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

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

}}

[[File:Laptop-intel-core2duo-t5500.jpg|thumb|Inside of a laptop, with the CPU removed from socket]]

{{anchor|DISCRETE-PROCESSOR}}

===Control unit===

{{main|Control unit}}

It directs the operation of the other units by providing timing and control signals. Most computer resources are managed by the CU. It directs the flow of data between the CPU and the other devices. [[John von Neumann]] included the control unit as part of the [[von Neumann architecture]]. In modern computer designs, the control unit is typically an internal part of the CPU with its overall role and operation unchanged since its introduction.<ref>{{Cite web|date=2018-09-24|title=Introduction of Control Unit and its Design|url=https://www.geeksforgeeks.org/introduction-of-control-unit-and-its-design/|access-date=2021-01-12|website=GeeksforGeeks|language=en-US|archive-date=2021-01-15|archive-url=https://web.archive.org/web/20210115072904/https://www.geeksforgeeks.org/introduction-of-control-unit-and-its-design/|url-status=live}}</ref>

===Arithmetic logic unit===

{{Main|Arithmetic logic unit}}

The arithmetic logic unit (ALU) is a digital circuit within the processor that performs integer arithmetic and [[bitwise logic]] operations. The inputs to the ALU are the data words to be operated on (called [[operands]]), status information from previous operations, and a code from the control unit indicating which operation to perform. Depending on the instruction being executed, the operands may come from [[processor register|internal CPU registers]], external memory, or constants generated by the ALU itself.

While performing various operations, CPUs need to calculate memory addresses required for fetching data from the memory; for example, in-memory positions of [[array element]]s must be calculated before the CPU can fetch the data from actual memory locations. Those address-generation calculations involve different [[integer arithmetic operation]]s, such as addition, subtraction, [[modulo operation]]s, or [[bit shift]]s. Often, calculating a memory address involves more than one general-purpose machine instruction, which do not necessarily [[Instruction cycle|decode and execute]] quickly. By incorporating an AGU into a CPU design, together with introducing specialized instructions that use the AGU, various address-generation calculations can be offloaded from the rest of the CPU, and can often be executed quickly in a single CPU cycle.

===Memory management unit (MMU)===

{{Main|Memory management unit}}

===Cache===

Other types of caches exist (that are not counted towards the "cache size" of the most important caches mentioned above), such as the [[translation lookaside buffer]] (TLB) that is part of the [[memory management unit]] (MMU) that most CPUs have.

===Clock rate===

===Clockless CPUs===

Rather than totally removing the clock signal, some CPU designs allow certain portions of the device to be asynchronous, such as using asynchronous [[Arithmetic logic unit|ALUs]] in conjunction with superscalar pipelining to achieve some arithmetic performance gains. While it is not altogether clear whether totally asynchronous designs can perform at a comparable or better level than their synchronous counterparts, it is evident that they do at least excel in simpler math operations. This, combined with their excellent power consumption and heat dissipation properties, makes them very suitable for [[embedded computer]]s.<ref>{{cite conference |author1=Garside, J. D. |author2=Furber, S. B. |author3= Chung, S-H | title = AMULET3 Revealed | publisher = [[University of Manchester]] Computer Science Department | year = 1999 | url = http://www.cs.manchester.ac.uk/apt/publications/papers/async99_A3.php |book-title=Proceedings, Fifth International Symposium on Advanced Research in Asynchronous Circuits and Systems |doi=10.1109/ASYNC.1999.761522 | archive-url=https://web.archive.org/web/20051210205845/http://www.cs.manchester.ac.uk/apt/publications/papers/async99_A3.php | archive-date=December 10, 2005 | url-status=dead| url-access=subscription }}</ref>

====Task-level parallelism====

{{Main|Multithreading (computer architecture)|l1=Multithreading|Multi-core processor}}

It was later recognized that finer-grain parallelism existed with a single program. A single program might have several threads (or functions) that could be executed separately or in parallel. Some of the earliest examples of this technology implemented [[input/output]] processing such as [[direct memory access]] as a separate thread from the computation thread. A more general approach to this technology was introduced in the 1970s when systems were designed to run multiple computation threads in parallel. This technology is known as [[Multithreading (computer architecture)|multi-threading]] (MT). The approach is considered more cost-effective than multiprocessing, as only a small number of components within a CPU are replicated to support MT as opposed to the entire CPU in the case of MP. In MT, the execution units and the memory system including the caches are shared among multiple threads. The downside of MT is that the hardware support for multithreading is more visible to software than that of MP and thus supervisor software like operating systems have to undergo larger changes to support MT. One type of MT that was implemented is known as [[temporal multithreading]], where one thread is executed until it is stalled waiting for data to return from external memory. In this scheme, the CPU would then quickly context switch to another thread which is ready to run, the switch often done in one CPU clock cycle, such as the [[UltraSPARC T1]]. Another type of MT is [[simultaneous multithreading]], where instructions from multiple threads are executed in parallel within one CPU clock cycle.

vCPU is not to be confused with a [[virtual private server]] (VPS).

=={{anchor|PCM}}Performance==

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Processing performance of computers is increased by using [[multi-core processor]]s, which essentially is plugging two or more individual processors (called ''cores'' in this sense) into one integrated circuit.<ref name="tt">{{Cite web

  | archive-date = 5 August 2010

  | archive-url = https://web.archive.org/web/20100805052158/http://searchdatacenter.techtarget.com/sDefinition/0,,sid80_gci1015740,00.html

  }}</ref> Ideally, a dual core processor would be nearly twice as powerful as a single core processor. In practice, the performance gain is far smaller, only about 50%, due to imperfect software algorithms and implementation.<ref>{{cite news|url=https://techspirited.com/quad-core-vs-dual-core|title=Quad Core Vs. Dual Core|newspaper=Tech Spirited |date=8 April 2010|access-date=7 November 2019|archive-date=4 July 2019|archive-url=https://web.archive.org/web/20190704093754/https://techspirited.com/quad-core-vs-dual-core|url-status=live |author1=Mlblevins }}</ref> Increasing the number of cores in a processor (i.e. dual-core, quad-core, etc.) increases the workload that can be handled. This means that the processor can now handle numerous asynchronous events, interrupts, etc. which can take a toll on the CPU when overwhelmed. These cores can be thought of as different floors in a processing plant, with each floor handling a different task. Sometimes, these cores will handle the same tasks as cores adjacent to them if a single core is not enough to handle the information. Multi-core CPUs enhance a computer's ability to run several tasks simultaneously by providing additional processing power. However, the increase in speed is not directly proportional to the number of cores added. This is because the cores need to interact through specific channels, and this inter-core communication consumes a portion of the available processing speed.<ref>{{Cite web |last=Marcin |first=Wieclaw |date=12 January 2022 |title=Factors Affecting Multi-Core Processors Performance |url=https://pcsite.co.uk/factors-affecting-multi-core-central-processing-unit-performance/ |website=PcSite}}</ref>

==Overclocking==

{{Main|Overclocking}}

==See also==