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{{Short description|Set of rules describing computer system}}
{{Lead too short|date=November 2023}}
[[File:Computer architecture block diagram.png|alt=|thumb|upright=1.35|Block diagram of a basic computer with uniprocessor CPU. Black lines indicate the flow of control signals, whereas red lines indicate the flow of processor instructions and data. Arrows indicate the direction of flow.]]
In [[computer science]] and [[computer engineering]], a '''computer architecture''' is the structure of a [[computer]] system made from component parts.<ref>{{cite web|last=Dragoni|first=Nicole|title=Introduction to peer to peer computing|url=http://www2.imm.dtu.dk/courses/02220/2017/L6/P2P.pdf|website=DTU Compute – Department of Applied Mathematics and Computer Science|___location=Lyngby, Denmark|date=n.d.}}</ref> It can sometimes be a high-level description that ignores details of the implementation.<ref>{{cite book|last1=Clements|first1=Alan|title=Principles of Computer Hardware|page=1|edition=Fourth|quote=Architecture describes the internal organization of a computer in an abstract way; that is, it defines the capabilities of the computer and its programming model. You can have two computers that have been constructed in different ways with different technologies but with the same architecture.}}</ref> At a more detailed level, the description may include the [[instruction set architecture]] design, [[microarchitecture]] design, [[logic design]], and [[implementation]].<ref>{{cite book|last1=Hennessy|first1=John|last2=Patterson|first2=David|title=Computer Architecture: A Quantitative Approach|page=11|edition=Fifth|quote=This task has many aspects, including instruction set design, functional organization, logic design, and implementation.}}</ref>
== History ==
The first documented computer architecture was in the correspondence between [[Charles Babbage]] and [[Ada Lovelace]], describing the [[analytical engine]]. While building the computer [[Z1 (computer)|Z1]] in 1936, [[Konrad Zuse]] described in two patent applications for his future projects that machine instructions could be stored in the same storage used for data, i.e., the [[Stored-program computer|stored-program]] concept.<ref>{{citation |title=Electronic Digital Computers |journal=Nature |date=25 September 1948 |volume=162 |page=487 |doi=10.1038/162487a0 |last1=Williams |first1=F. C. |last2=Kilburn |first2=T. |issue=4117 |bibcode=1948Natur.162..487W |s2cid=4110351 |doi-access=free }}</ref><ref>Susanne Faber, "Konrad Zuses Bemuehungen um die Patentanmeldung der Z3", 2000</ref> Two other early and important examples are:
* [[John von Neumann]]'s 1945 paper, [[First Draft of a Report on the EDVAC]], which described an organization of logical elements;<ref>{{Cite book|title=First Draft of a Report on the EDVAC|last=Neumann|first=John|year=1945|pages=9}}</ref> and
*[[Alan M. Turing|Alan Turing]]'s more detailed ''Proposed Electronic Calculator'' for the [[Automatic Computing Engine]], also 1945 and which cited [[John von Neumann]]'s paper.<ref>Reproduced in B. J. Copeland (Ed.), "Alan Turing's Automatic Computing Engine", Oxford University Press, 2005, pp. 369–454.</ref>
The term "architecture" in computer literature can be traced to the work of Lyle R. Johnson and [[Fred Brooks|Frederick P. Brooks, Jr.]], members of the Machine Organization department in IBM's main research center in 1959. Johnson had the opportunity to write a proprietary research communication about the [[IBM 7030 Stretch|Stretch]], an IBM-developed [[supercomputer]] for [[Los Alamos National Laboratory]] (at the time known as Los Alamos Scientific Laboratory). To describe the level of detail for discussing the luxuriously embellished computer, he noted that his description of formats, instruction types, hardware parameters, and speed enhancements were at the level of "system architecture", a term that seemed more useful than "machine organization".<ref>{{cite web|url=https://archive.computerhistory.org/resources/text/IBM/Stretch/pdfs/05-10/102634114.pdf |last1= Johnson |first1=Lyle| title= A Description of Stretch|page=1|year=1960|access-date=7 October 2017}}</ref>
Subsequently, Brooks, a Stretch designer, opened Chapter 2 of a book called ''Planning a Computer System: Project Stretch'' by stating, "Computer architecture, like other architecture, is the art of determining the needs of the user of a structure and then designing to meet those needs as effectively as possible within economic and technological constraints."<ref>{{Cite book |title= Planning a Computer System|last=Buchholz |first=Werner|year=1962|pages=5}}</ref>
Brooks went on to help develop the [[IBM System/360]] line of computers, in which "architecture" became a noun defining "what the user needs to know".<ref>{{Cite web|url=http://www-03.ibm.com/ibm/history/ibm100/us/en/icons/system360/|archive-url=https://web.archive.org/web/20120403020049/http://www-03.ibm.com/ibm/history/ibm100/us/en/icons/system360/|url-status=dead|archive-date=April 3, 2012|title=System 360, From Computers to Computer Systems|website=IBM100|date=7 March 2012|access-date=11 May 2017}}</ref> The System/360 line was succeeded by several compatible lines of computers, including the current [[IBM Z]] line. Later, computer users came to use the term in many less explicit ways.<ref>{{cite book|last1=Hellige|first1=Hans Dieter|title=Geschichten der Informatik: Visionen, Paradigmen, Leitmotive|chapter=Die Genese von Wissenschaftskonzeptionen der Computerarchitektur: Vom "system of organs" zum Schichtmodell des Designraums| pages=411–472|year=2004}}</ref>
The earliest computer architectures were designed on paper and then directly built into the final hardware form.<ref>ACE underwent seven paper designs in one year, before a prototype was initiated in 1948. [B. J. Copeland (Ed.), "Alan Turing's Automatic Computing Engine", OUP, 2005, p. 57]</ref>
Later, computer architecture prototypes were physically built in the form of a [[transistor–transistor logic]] (TTL) computer—such as the prototypes of the [[Motorola 6800#Development team|6800]] and the [[PA-RISC]]—tested, and tweaked, before committing to the final hardware form.
As of the 1990s, new computer architectures are typically "built", tested, and tweaked—inside some other computer architecture in a [[computer architecture simulator]]; or inside a FPGA as a [[soft microprocessor]]; or both—before committing to the final hardware form.<ref>{{Cite web|url=https://www.cise.ufl.edu/~mssz/CompOrg/CDAintro.html|title=Organization of Computer Systems|last=Schmalz|first=M.S.|website=UF CISE|access-date=11 May 2017}}</ref>
== Subcategories ==
The discipline of computer architecture has three main subcategories:<ref name=HennessyPattersonQuantitative>{{cite book|author=John L. Hennessy and David A. Patterson|title=Computer Architecture: A Quantitative Approach|edition=Third|publisher=Morgan Kaufmann Publishers}}</ref>
* '''[[Instruction set architecture]]''' (ISA): defines the [[machine code]] that a [[computer processor|processor]] reads and acts upon as well as the [[word size]], [[addressing mode|memory address modes]], [[processor register]]s, and [[data type]].
* '''[[Microarchitecture]]''': also known as "computer organization", this describes how a particular [[Central processing unit|processor]] will implement the ISA.<ref>{{cite book|title= Dictionary of Computer Science, Engineering, and Technology|last=Laplante|first=Phillip A.|year=2001|publisher=CRC Press|isbn=0-8493-2691-5|pages=94–95}}</ref> The size of a computer's [[CPU cache]] for instance, is an issue that generally has nothing to do with the ISA.
* '''[[Systems design]]''': includes all of the other hardware components within a computing system, such as data processing other than the CPU (e.g., [[direct memory access]]), [[virtualization]], and [[multiprocessing]].
There are other technologies in computer architecture. The following technologies are used in bigger companies like Intel, and were estimated in 2002<ref name=HennessyPattersonQuantitative /> to count for 1% of all of computer architecture:
* '''Macroarchitecture''': [[architectural layer]]s more abstract than microarchitecture
* '''Assembly instruction set architecture''': A smart assembler may convert an abstract [[assembly language]] common to a group of machines into slightly different [[machine language]] for different [[implementation]]s.
* '''Programmer-visible macroarchitecture''': higher-level language tools such as [[compiler]]s may define a consistent interface or contract to [[programmer]]s using them, abstracting differences between underlying ISAs and [[microarchitecture]]s. For example, the [[C (programming language)|C]], [[C++]], or [[Java (programming language)|Java]] standards define different programmer-visible macroarchitectures.
* '''[[Microcode]]''': microcode is software that translates instructions to run on a chip. It acts like a wrapper around the hardware, presenting a preferred version of the hardware's instruction set interface. This instruction translation facility gives chip designers flexible options: E.g. 1. A new improved version of the chip can use microcode to present the exact same instruction set as the old chip version, so all software targeting that instruction set will run on the new chip without needing changes. E.g. 2. Microcode can present a variety of instruction sets for the same underlying chip, allowing it to run a wider variety of software.
* '''Pin architecture''': The hardware functions that a [[microprocessor]] should provide to a hardware platform, e.g., the [[x86]] pins A20M, FERR/IGNNE or FLUSH. Also, messages that the processor should emit so that external [[CPU cache|caches]] can be invalidated (emptied). Pin architecture functions are more flexible than ISA functions because external hardware can adapt to new encodings, or change from a pin to a message. The term "architecture" fits, because the functions must be provided for compatible systems, even if the detailed method changes.
==Roles==
===Definition===
Computer architecture is concerned with balancing the performance, efficiency, cost, and reliability of a computer system. The case of instruction set architecture can be used to illustrate the balance of these competing factors. More complex [[instruction set]]s enable programmers to write more space efficient programs, since a single instruction can encode some higher-level abstraction (such as the [[X86 instruction listings|x86 Loop instruction]]).<ref>{{cite book |last1=Null |first1=Linda |title=The Essentials of Computer Organization and Architecture |date=2019 |publisher=Jones & Bartlett Learning |___location=Burlington, MA |isbn=9781284123036 |page=280 |edition=5th}}</ref> However, longer and more complex instructions take longer for the [[Processor (computing)|processor]] to decode and can be more costly to implement effectively. The increased complexity from a large instruction set also creates more room for unreliability when instructions interact in unexpected ways.
The implementation involves [[integrated circuit design]], packaging, [[Electric power|power]], and [[Computer cooling|cooling]]. Optimization of the design requires familiarity with topics from [[compiler]]s and [[operating system]]s to [[logic design]] and packaging.<ref>{{Cite web|url=https://www.cis.upenn.edu/~milom/cis501-Fall11/lectures/00_intro.pdf|title=What is computer architecture?|last=Martin|first=Milo|website=UPENN|access-date=11 May 2017}}</ref>
===Instruction set architecture===
{{Main|Instruction set architecture}}
An [[instruction set architecture]] (ISA) is the interface between the computer's software and hardware and also can be viewed as the programmer's view of the machine. Computers do not understand [[high-level programming language]]s such as [[Java (programming language)|Java]], [[C++]], or most programming languages used. A processor only understands instructions encoded in some numerical fashion, usually as [[Binary numeral system|binary number]]s. Software tools, such as [[compiler]]s, translate those high level languages into instructions that the processor can understand.<ref>{{cite web |title=Glossary |url=https://codasip.com/glossary/isa |website=Codasip |access-date=30 May 2025}}</ref><ref>{{cite web |title=What is Instruction Set Architecture (ISA)? |url=https://www.arm.com/glossary/isa |website=The Architecture for the Digital World |access-date=30 May 2025 |language=en}}</ref>
Besides instructions, the ISA defines items in the computer that are available to a program—e.g., [[data type]]s, [[Processor register|registers]], [[addressing mode]]s, and [[Computer memory|memory]]. Instructions locate these available items with register indexes (or names) and memory addressing modes.<ref>{{cite web |title=Organization of Computer Systems: ISA, Machine Language, Number Systems |url=https://www.cise.ufl.edu/~mssz/CompOrg/CDA-lang.html |website=www.cise.ufl.edu |access-date=30 May 2025}}</ref><ref>{{cite web |title=Instruction Set Architecture – Computer Architecture |url=https://www.cs.umd.edu/~meesh/411/CA-online/chapter/instruction-set-architecture/index.html |website=www.cs.umd.edu |access-date=30 May 2025}}</ref>
The ISA of a computer is usually described in a small instruction manual, which describes how the instructions are encoded. Also, it may define short (vaguely) mnemonic names for the instructions. The names can be recognized by a software development tool called an [[assembler (computer programming)|assembler]]. An assembler is a computer program that translates a human-readable form of the ISA into a computer-readable form. [[Disassembler]]s are also widely available, usually in [[debugger]]s and software programs to isolate and correct malfunctions in binary computer programs.<ref>{{cite book |last1=Hennessy |first1=John L. |last2=Patterson |first2=David A. |title=Computer Architecture: A Quantitative Approach |date=23 November 2017 |publisher=[[Morgan Kaufmann Publishers]] |isbn=978-0-12-811906-8 |url=https://google.com/books/edition/Computer_Architecture/cM8mDwAAQBAJ |access-date=30 May 2025 |language=en}}</ref>
ISAs vary in quality and completeness. A good ISA compromises between [[programmer]] convenience (how easy the code is to understand), size of the code (how much code is required to do a specific action), cost of the [[computer]] to interpret the instructions (more complexity means more hardware needed to decode and execute the instructions), and speed of the computer (with more complex decoding hardware comes longer decode time). [[Memory organisation|Memory organization]] defines how instructions interact with the memory, and how memory interacts with itself.
During design [[Emulator|emulation]], emulators can run programs written in a proposed instruction set. Modern emulators can measure size, cost, and speed to determine whether a particular ISA is meeting its goals.
===Computer organization===
{{main | Microarchitecture}}
Computer organization helps optimize performance-based products. For example, software engineers need to know the [[processing power]] of [[Processor (computing)|processors]]. They may need to optimize software in order to gain the most performance for the lowest price. This can require quite a detailed analysis of the computer's organization. For example, in an [[SD card]], the designers might need to arrange the card so that the most data can be processed in the fastest possible way.
Computer organization also helps plan the selection of a processor for a particular project. [[Multimedia]] projects may need very rapid data access, while [[virtual machine]]s may need fast interrupts. Sometimes certain tasks need additional components as well. For example, a computer capable of running a virtual machine needs [[virtual memory]] hardware so that the memory of different virtual computers can be kept separated. Computer organization and features also affect power consumption and processor cost.
===Implementation===
Once an [[Instruction set architecture|instruction set]] and [[microarchitecture]] have been designed, a practical machine must be developed. This design process is called the ''implementation''. Implementation is usually not considered architectural design, but rather hardware [[Engineering design process|design engineering]]. Implementation can be further broken down into several steps:
* '''Logic implementation''' designs the circuits required at a [[Logic gate|logic-gate]] level.
* '''Circuit implementation''' does [[transistor]]-level designs of basic elements (e.g., gates, [[multiplexer]]s, [[Flip-flop (electronics)|latches]]) as well as of some larger blocks ([[Arithmetic logic unit|ALU]]s, caches etc.) that may be implemented at the logic-gate level, or even at the physical level if the design calls for it.
* '''Physical implementation''' draws physical circuits. The different circuit components are placed in a chip [[Floorplan (microelectronics)|floor plan]] or on a board and the wires connecting them are created.
* '''Design validation''' tests the computer as a whole to see if it works in all situations and all timings. Once the design validation process starts, the design at the logic level are tested using logic emulators. However, this is usually too slow to run a realistic test. So, after making corrections based on the first test, prototypes are constructed using Field-Programmable Gate-Arrays ([[FPGA]]s). Most hobby projects stop at this stage. The final step is to test prototype integrated circuits, which may require several redesigns.
For [[Central processing unit|CPU]]s, the entire implementation process is organized differently and is often referred to as [[CPU design]].
==Design goals==
The exact form of a computer system depends on the constraints and goals. Computer architectures usually trade off standards, [[Electric power|power]] versus [[Computer performance|performance]], cost, memory capacity, [[latency (engineering)|latency]] (latency is the amount of time that it takes for information from one node to travel to the source) and throughput. Sometimes other considerations, such as features, size, weight, reliability, and expandability are also factors.
The most common
===Performance===
Modern computer performance is often described in [[instructions per cycle]] (IPC), which measures the efficiency of the architecture at any clock frequency; a faster IPC rate means the computer is faster. Older computers had IPC counts as low as 0.1 while modern processors easily reach nearly 1. [[Superscalar]] processors may reach three to five IPC by executing several instructions per clock cycle.{{citation needed|date=January 2020}}
Counting machine-language instructions would be misleading because they can do varying amounts of work in different ISAs. The "instruction" in the standard measurements is not a count of the ISA's machine-language instructions, but a unit of measurement, usually based on the speed of the [[VAX]] computer architecture.
Many people used to measure a computer's speed by the [[clock rate]] (usually in [[MHz]] or GHz). This refers to the cycles per second of the main clock of the [[Central processing unit|CPU]]. However, this metric is somewhat misleading, as a machine with a higher clock rate may not necessarily have greater performance. As a result, manufacturers have moved away from clock speed as a measure of performance.
There are two main types of speed: [[Latency (engineering)|latency]] and [[throughput]]. Latency is the time between the start of a process and its completion. Throughput is the amount of work done per unit time. [[Interrupt latency]] is the guaranteed maximum response time of the system to an electronic event (like when the disk drive finishes moving some data).
Performance is affected by a very wide range of design choices — for example, [[Pipeline (computing)|pipelining]] a processor usually makes latency worse, but makes throughput better. Computers that control machinery usually need low interrupt latencies. These computers operate in a [[real-time computing|real-time]] environment and fail if an operation is not completed in a specified amount of time. For example, computer-controlled anti-lock brakes must begin braking within a predictable and limited time period after the brake pedal is sensed or else failure of the brake will occur.
[[Benchmark (computing)|Benchmarking]] takes all these factors into account by measuring the time a computer takes to run through a series of test programs. Although benchmarking shows strengths, it should not be how you choose a computer. Often the measured machines split on different measures. For example, one system might handle scientific applications quickly, while another might render [[video game]]s more smoothly. Furthermore, designers may target and add special features to their products, through hardware or software, that permit a specific benchmark to execute quickly but do not offer similar advantages to general tasks.
==
{{Main|Low-power electronics|Performance per watt}}
Power efficiency is another important measurement in modern computers. Higher power efficiency can often be traded for lower speed or higher cost. The typical measurement when referring to power consumption in computer architecture is MIPS/W (millions of instructions per second per watt).
Modern circuits have less power required per [[transistor]] as the number of transistors per chip grows.<ref>{{Cite web|url=http://eacharya.inflibnet.ac.in/data-server/eacharya-documents/53e0c6cbe413016f23443704_INFIEP_33/192/ET/33-192-ET-V1-S1__ssed_unit_4_module_10_integrated_circuits_and_fabrication_e-text.pdf|title=Integrated circuits and fabrication|access-date=8 May 2017}}</ref> This is because each transistor that is put in a new chip requires its own power supply and requires new pathways to be built to power it.{{Clarify|reason=The last two sentences seem to contradict each other|date=March 2025}} However, the number of transistors per chip is starting to increase at a slower rate. Therefore, power efficiency is starting to become as important, if not more important than fitting more and more transistors into a single chip. Recent processor designs have shown this emphasis as they put more focus on power efficiency rather than cramming as many transistors into a single chip as possible.<ref>{{Cite web|url=http://www.samsung.com/semiconductor/minisite/Exynos/w/solution/mod_ap/8895/?CID=AFL-hq-mul-0813-11000170|title=Exynos 9 Series (8895)|website=Samsung|access-date=8 May 2017}}</ref> In the world of [[embedded computers]], power efficiency has long been an important goal next to throughput and latency.
===Shifts in market demand===
Increases in clock frequency have grown more slowly over the past few years, compared to power reduction improvements. This has been driven by the end of [[Moore's Law]] and demand for longer [[battery life]] and reductions in size for [[mobile technology]]. This change in focus from higher clock rates to power consumption and miniaturization can be shown by the significant reductions in power consumption, as much as 50%, that were reported by [[Intel]] in their release of the [[Haswell (microarchitecture)|Haswell microarchitecture]]; where they dropped their power consumption benchmark from 30–40 [[watt]]s down to 10–20 watts.<ref>{{Cite web|url=http://www.intel.com/content/dam/doc/white-paper/resources-xeon-measuring-processor-power-paper.pdf|title=Measuring Processor Power TDP vs ACP|date=April 2011|website=Intel|access-date=5 May 2017}}</ref> Comparing this to the processing speed increase of 3 GHz to 4 GHz (2002 to 2006), it can be seen that the focus in research and development is shifting away from clock frequency and moving towards consuming less power and taking up less space.<ref>{{Cite web |date=24 April 2012 |title=History of Processor Performance |url=https://www.cs.columbia.edu/~sedwards/classes/2012/3827-spring/advanced-arch-2011.pdf |access-date=5 May 2017 |website=cs.columbia.edu}}</ref>
==See also==
{{Portal|Electronics}}
{{cmn|colwidth=30em|
* [[Bit-serial architecture]]
* [[Comparison of CPU architectures]]
* [[Computer hardware]]
* [[CPU design]]
* [[
* [[Floating point]]
* [[Flynn's taxonomy]]
* [[Harvard architecture]] ([[Modified Harvard architecture|Modified]])
* [[Influence of the IBM PC on the personal computer market]]
* [[Orthogonal instruction set]]
* [[Reconfigurable computing]]
* [[Software architecture]]
* [[Transport triggered architecture]]
* [[Von Neumann architecture]]
}}
==References==
{{Reflist}}
==Sources==
* {{Cite book |last=[[John L. Hennessy]] and [[David Patterson (scientist)|David Patterson]] |title=Computer Architecture: A Quantitative Approach |publisher=Morgan Kaufmann |edition=Fourth |year=2006 |isbn=978-0-12-370490-0 |url=http://www.elsevierdirect.com/product.jsp?isbn=9780123704900}}
* [[Robert S. Barton|Barton, Robert S.]], "Functional Design of Computers", ''Communications of the ACM'' 4(9): 405 (1961).
* Barton, Robert S., "A New Approach to the Functional Design of a Digital Computer", ''Proceedings of the Western Joint Computer Conference'', May 1961, pp. 393–396. About the design of the Burroughs [[Burroughs large systems|B5000]] computer.
* [[Gordon Bell|Bell, C. Gordon]]; and [[Allen Newell|Newell, Allen]] (1971). [http://research.microsoft.com/en-us/um/people/gbell/Computer_Structures__Readings_and_Examples/contents.html "Computer Structures: Readings and Examples"], McGraw-Hill.
* [[Gerrit Blaauw|Blaauw, G.A.]], and [[Fred Brooks|Brooks, F.P., Jr.]], [http://domino.research.ibm.com/tchjr/journalindex.nsf/d9f0a910ab8b637485256bc80066a393/95dc427e3fd3024a85256bfa006859f7?OpenDocument "The Structure of System/360, Part I-Outline of the Logical Structure"], ''IBM Systems Journal'', vol. 3, no. 2, pp. 119–135, 1964.
* {{Cite book |last= Tanenbaum |first=Andrew S. |author-link=Andrew S. Tanenbaum |title=Structured Computer Organization |year=1979 |publisher=Prentice-Hall |___location=[[Englewood Cliffs, New Jersey]] |isbn=0-13-148521-0}}
==External links==
{{Commons category}}
* [https://www.youtube.com/user/cmu18447 Carnegie Mellon Computer Architecture Lectures]
* [http://portal.acm.org/toc.cfm?id=SERIES416&type=series&coll=GUIDE&dl=GUIDE&CFID=41492512&CFTOKEN=82922478 ISCA: Proceedings of the International Symposium on Computer Architecture]
* [http://www.microarch.org/ Micro: IEEE/ACM International Symposium on Microarchitecture]
* [https://web.archive.org/web/20050528085407/http://www.hpcaconf.org/ HPCA: International Symposium on High Performance Computer Architecture]
* [http://portal.acm.org/toc.cfm?id=SERIES311&type=series&coll=GUIDE&dl=GUIDE&CFID=41492415&CFTOKEN=3676847 ASPLOS: International Conference on Architectural Support for Programming Languages and Operating Systems]
* [http://www.acm.org/taco/ ACM Transactions on Architecture and Code Optimization]
* [https://www.computer.org/csdl/journal/tc IEEE Transactions on Computers]
* {{webarchive|url=https://web.archive.org/web/20171031185802/http://www-scf.usc.edu/~inf520/downloads/The%20von%20Neumann%20Architecture%20of%20Computer%20Systems.pdf|title=The von Neumann Architecture of Computer Systems|date=2017-10-31}}
{{Computer science}}
{{Digital electronics}}
{{Authority control}}
[[Category:Computer architecture| ]]
[[Category:Central processing unit]]
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