Editing Harvard architecture (section)

{{Short description|Computer architecture where code and data each have a separate bus}}
{{Use American English|date = March 2019}}
{{For|the architecture program at Harvard University|Harvard Graduate School of Design}}
{{Refimprove|date=March 2011}}
[[File:Harvard architecture.svg|thumb|Harvard architecture|362x362px]]

The '''Harvard architecture''' is a [[computer architecture]] with separate [[computer storage|storage]]<ref>{{Cite book |last=Noergaard |first=Tammy |url=https://books.google.com/books?id=M0g0GjY5IWQC&dq=%22Harvard+architecture%22+-wikipedia&pg=PA146 |title=Embedded Systems Architecture: A Comprehensive Guide for Engineers and Programmers |date=2005 |publisher=Newnes |isbn=978-0-7506-7792-9 |language=en}}</ref> and signal pathways for [[Machine code|instructions]] and [[data]]. It is often contrasted with the [[von Neumann architecture]], where program instructions and data share the same memory and pathways. This architecture is often used in real-time processing or low-power applications.<ref>{{cite conference |last1=Kong |first1=J. H. |last2=Ang |first2=L. M. |last3=Seng |first3=K. P. |title=Minimal Instruction Set AES Processor using Harvard Architecture |conference=2010 3rd International Conference on Computer Science and Information Technology |date=2010 |volume=9 |pages=65–69 |doi=10.1109/ICCSIT.2010.5564522 |isbn=978-1-4244-5537-9 |url=https://ieeexplore.ieee.org/document/5564522|url-access=subscription }}</ref><ref>{{cite conference |last1=Venkatesan |first1=Chandran |last2=Sulthana |first2=M. Thabsera |last3=Sumithra |first3=M. G. |last4=Suriya |first4=M. |conference=2019 5th International Conference on Advanced Computing & Communication Systems (ICACCS) |title=Design of a 16-Bit Harvard Structure RISC Processor in Cadence 45nm Technology |date=2019 |pages=173–178 |doi=10.1109/ICACCS.2019.8728479 |isbn=978-1-5386-9531-9 |url=https://ieeexplore.ieee.org/document/8728479|url-access=subscription }}</ref>

The term is often stated as having originated from the [[Harvard Mark I]]<ref>{{Cite book |last=Furber |first=S. B. |url=https://books.google.com/books?id=RkxnDwAAQBAJ&dq=%22Harvard+architecture%22+-wikipedia&pg=PT22 |title=VLSI Risc Architecture and Organization |date=2017-09-19 |publisher=Routledge |isbn=978-1-351-40537-9 |language=en}}</ref> relay-based computer, which stored instructions on [[punched tape]] (24 bits wide) and data in [[electro-mechanical]] counters. These early machines had data storage entirely contained within the [[central processing unit]], and provided no access to the instruction storage as data. Programs needed to be loaded by an operator; the processor could not [[Booting|initialize]] itself. However, in the only peer-reviewed paper on the topic published in 2022 the author states that:<ref>{{cite journal |last1=Pawson |first1=Richard |date=30 September 2022 |title=The Myth of the Harvard Architecture |url=https://ieeexplore.ieee.org/document/9779481 |journal=IEEE Annals of the History of Computing |volume=44 |issue=3 |pages=59–69 |doi=10.1109/MAHC.2022.3175612 |s2cid=252018052|url-access=subscription }}</ref><ref>{{Cite |last=Pawson |first=Richard |title=The Myth of the Harvard Architecture |date=2022 |url=https://metalup.org/harvardarchitecture/The%20Myth%20of%20the%20Harvard%20Architecture.pdf}}</ref> 

* 'The term "Harvard architecture" was coined decades later, in the context of microcontroller design' and only 'retrospectively applied to the Harvard machines and subsequently applied to RISC microprocessors with separated caches';

* 'The so-called "Harvard" and "von Neumann" architectures are often portrayed as a [[dichotomy]], but the various devices labeled as the former have far more in common with the latter than they do with each other';

* 'In short [the Harvard architecture] isn't an architecture and didn't derive from work at Harvard'.

Modern processors appear to the user to be systems with von Neumann architectures, with the program code stored in the same [[main memory]] as the data. For performance reasons, internally and largely invisible to the user, most designs have separate [[CPU cache|processor caches]] for the instructions and data, with separate pathways into the processor for each. This is one form of what is known as the [[modified Harvard architecture]].

Harvard architecture is historically, and traditionally, split into two address spaces, but having three, i.e. two extra (and all accessed in each cycle) is also done,<ref>{{Cite web |url=http://file.elecfans.com/web1/M00/7F/5E/o4YBAFwnAoOAInZLABl9vXqLkQY788.pdf |date=July 2006 |title=Kalimba DSP: User guide |quote=this is a three-bank Harvard architecture. |access-date=2022-09-23 |page=18}}</ref> while rare.