Editing Harvard Mark I

{{Short description|Early American electromechanical computer (1944)}}
{{use mdy dates|date=July 2022}}
{{Infobox information appliance
| name = Harvard Mark I
| image = Harvard Mark I Computer - Input-Output Details.jpg
| image_size = 
| alt = 
| caption = Closeup of input/output and control readers
| aka = [[IBM]] Automatic Sequence Controlled Calculator (ASCC)
| developer = [[Howard H. Aiken|Howard Aiken]] / [[IBM]]
| manufacturer = 
| type = 
| releasedate = {{Start date and age|1944|08|07}}
| price = 
| connectivity = 
| lifespan = 
| unitssold = 
| media = 
| os = <!-- operating system -->
| input = 
| camera = 
| power = {{cvt|5|hp}}
| cpu = 
| CPUspeed = 
| storage = 
| memory = 
| RAMtype = 
| display = 
| audio = 
| service = <!-- online service/s offered -->
| dimensions = {{ubl
| {{cvt|816|cuft}}:
| Width: {{cvt|51|ft}}
| Height: {{cvt|8|ft}}
| Depth: {{cvt|2|ft}}
}}| weight = {{cvt|9,445|lb|kg}}
| touchpad = 
| predecessor = 
| successor = [[Harvard Mark II]]
| related = 
}}
[[File:Harvard Mark I Computer - Left Segment.jpg|thumb|right|250px|The left end consisted of electromechanical computing components.]]
[[File:Harvard Mark I Computer - Right Segment.JPG|thumb|right|250px|The right end included data and program readers, and automatic typewriters.]]
The '''Harvard Mark I''', or [[IBM]] '''Automatic Sequence Controlled Calculator''' ('''ASCC'''), was one of the earliest general-purpose [[electromechanical]] [[computer]]s used in the war effort during the last part of [[World War II]].

One of the first programs to run on the Mark I was initiated on 29 March 1944{{sfnp|Cohen|2000|p=164}} by [[John von Neumann]]. At that time, von Neumann was working on the [[Manhattan Project]], and needed to determine whether [[Implosion-type nuclear weapon|implosion]] was a viable choice to detonate the atomic bomb that would be used a year later. The Mark I also computed and printed mathematical tables, which had been the initial goal of British inventor [[Charles Babbage]] for his [[analytical engine]] in 1837.

According to [[Edmund Berkeley]], the operators of the Mark I often called the machine "Bessy, the Bessel engine", after [[Bessel functions]].<ref>Berkeley, Edmund Callis. Giant Brains, or, Machines That Think (Classics To Go) (p. 6). Otbebookpublishing. Kindle Edition.</ref>

The Mark I was disassembled in 1959; part of it was given to IBM, part went to the [[Smithsonian Institution]], and part entered the [[Harvard Collection of Historical Scientific Instruments]]. For decades, Harvard's portion was on display in the lobby of the Aiken Computation Lab. About 1997, it was moved to the [[Harvard Science Center]]. In 2021, it was moved again, to the lobby of Harvard's new Science and Engineering Complex in [[Allston|Allston, Massachusetts]].<ref>{{cite web |last1=Powell |first1=Alvin |title=Harvard's Mark 1 finds its new home |url=https://news.harvard.edu/gazette/story/2021/07/harvards-mark-1-finds-its-new-home/ |website=Harvard Gazette |access-date=2023-08-17 |date=23 July 2021}}</ref>

==Origins==
The origins of the Harvard Mark I can be traced back to 1935, when [[Howard H. Aiken|Howard Aiken]] conceived of building a powerful, large-scale calculating machine while pursuing graduate studies in physics at [[Harvard University]]. Aiken presented his proposal for an automatic calculating machine to IBM in November 1937.{{sfnp|Cohen|2000|p=53}}<ref name="Harvard1DEV">{{cite web|url=https://www.historyofinformation.com/detail.php?id=624|title=Key Aspects of the Development of the Harvard Mark 1 and its Software|author=[[Howard H. Aiken|Howard Aiken]] and [[Grace Hopper]]|work=History of Information|access-date=April 7, 2025}}</ref> The concept was intended to solve advanced mathematical problems.<ref name="HarvardMarkDEV">{{cite video|url=https://m.youtube.com/watch?v=vqnh2Gi13TY|date=June 2, 2024|title=Harvard Secret Computer Lab|author=Computer History Archives Project|work=[[YouTube]]}}</ref> After a feasibility study by IBM engineers, the company chairman [[Thomas J. Watson|Thomas Watson Sr.]] personally approved the project and its funding in February 1939.

Howard Aiken had started to look for a company to design and build his calculator in early 1937. After two rejections,<ref>{{harvp|Cohen|2000|p=39}}: It was first rejected by the [[Monroe Calculator Company]] and then by Harvard University.</ref> he was shown a demonstration set that [[Charles Babbage]]’s son had given to Harvard University 70 years earlier.  This led him to study Babbage and to add references to the [[Analytical Engine]] to his proposal; the resulting machine "brought Babbage’s principles of the Analytical Engine almost to full realization, while adding important new features."<ref>{{cite web|url=http://www-03.ibm.com/ibm/history/exhibits/markI/markI_intro2.html |archive-url=https://web.archive.org/web/20050308062419/http://www-03.ibm.com/ibm/history/exhibits/markI/markI_intro2.html |url-status=dead |archive-date=March 8, 2005 |title=IBM's ASCC introduction 2|date= January 23, 2003 |access-date=14 December 2013}}</ref>

In 1941, Aiken had to put the project on hiatus, as he was called into active naval service in [[World War II]].<ref name="HarvardMarkDEV"/> The ASCC was developed and built by IBM at their [[Endicott, New York|Endicott]] plant in early 1943, and it was shipped to [[Harvard]] in February 1944.<ref name="Harvard1DEV"/> It began computations for the US Navy Bureau of Ships in May and was officially presented to the university on August 7, 1944.<ref>{{cite journal|title=Proposed automatic calculating machine (Abstract)|journal=IEEE Spectrum|date=August 1964|volume=1|issue=8|pages=62–69|doi=10.1109/MSPEC.1964.6500770|publisher=IEEE Xplore|s2cid=51652725 |issn=0018-9235}}</ref>

Although not the [[Z3 (computer)|first working computer]], the machine was the first to automate the execution of complex calculations, making it a significant step forward for computing.<ref>{{cite web | url=https://history-computer.com/the-history-of-harvard-mark-1/ | title=The History of Harvard Mark 1: A Complete Guide | date=September 21, 2021 }}</ref>

==Design and construction==
The ASCC was built from [[switch]]es, [[relay]]s, [[Pinwheel calculator|rotating shaft]]s, and [[clutch]]es. It used 765,000 [[electromechanical]] components and hundreds of miles of wire, comprising a volume of {{Convert|816|cuft|4=0}} – {{convert|51|ft|m}} in length, {{convert|8|ft|m}} in height, and {{convert|2|ft|m}} deep. It weighed about {{convert|9,445|lb|ST MT|1}}.<ref>{{cite web |title=IBM Archives: Feeds, speeds and specifications ASCC Statistics |url=http://www-03.ibm.com/ibm/history/exhibits/markI/markI_feeds2.html |archive-url=https://web.archive.org/web/20051206102153/http://www-03.ibm.com/ibm/history/exhibits/markI/markI_feeds2.html |url-status=dead |archive-date=December 6, 2005 |website=www-03.ibm.com |date=23 January 2003}}</ref> The basic calculating units had to be synchronized and  powered mechanically, so they were operated by a {{convert|50|ft|m|adj=on}} [[drive shaft]] coupled to a {{convert|5|hp|}} electric motor, which served as the main power source and [[Clock generator|system clock]]. From the IBM Archives:

<blockquote>The Automatic Sequence Controlled Calculator (Harvard Mark I) was the first operating machine that could execute long computations automatically. A project conceived by Harvard University’s Dr. Howard Aiken, the Mark I was built by IBM engineers in Endicott, N.Y. A steel frame 51 feet long and 8 feet high held the calculator, which consisted of an interlocking panel of small gears, counters, switches and control circuits, all only a few inches in depth. The ASCC used {{convert|500|mi|km}} of wire with three million connections, 3,500 multipole relays with 35,000 contacts, 2,225 counters, 1,464 tenpole switches and tiers of 72 adding machines, each with 23 significant numbers. It was the industry’s largest electromechanical calculator.<ref>[https://web.archive.org/web/20041217213509/http://www-03.ibm.com/ibm/history/reference/faq_0000000011.html IBM Archives: FAQ / Products and Services]</ref></blockquote>

The enclosure for the Mark I was designed by futuristic American [[industrial designer]] [[Norman Bel Geddes]] at IBM's expense.  Aiken was annoyed that the cost ($50,000 or more according to [[Grace Hopper]]) was not used to build additional computer equipment.<ref>{{cite web |series=Computer Oral History Collection, 1969–1973, 1977 |title=Grace Murray Hopper Interview |date=January 7, 1969 |publisher=Archives Center, National Museum of American History |url=http://invention.smithsonian.org/downloads/fa_cohc_tr_hopp690107.pdf |access-date=2012-10-21 |url-status=dead |archive-url=https://web.archive.org/web/20120223191745/http://invention.smithsonian.org/downloads/fa_cohc_tr_hopp690107.pdf |archive-date=2012-02-23 |pages=7–8}}</ref>

==Operation==
The Mark I had 60 sets of 24 switches for manual data entry and could store 72 numbers, each 23 decimal digits long.<ref name="wilkes"/>  It could do 3 additions or subtractions in a second. A multiplication took 6 seconds, a division took 15.3 seconds, and a logarithm or a trigonometric function took over one minute.{{sfnp|Campbell|1999|p=43}}

The Mark I read its [[Instruction set|instruction]]s from a 24-channel [[punched tape|punched paper tape]]. It executed the current instruction and then read the next one. A separate tape could contain numbers for input, but the tape formats were not interchangeable. Instructions could not be executed from the storage registers. Because instructions were not stored in working memory, it is widely claimed that the Harvard Mark I was the origin of the [[Harvard architecture]]. However, this is disputed in ''The Myth of the Harvard Architecture'' published in the ''IEEE Annals of the History of Computing'',<ref>{{cite journal |last1=Pawson |first1=Richard |title=The Myth of the Harvard Architecture |journal=IEEE Annals of the History of Computing |date=30 September 2022 |volume=44 |issue=3 |pages=59–69 |doi=10.1109/MAHC.2022.3175612 |s2cid=252018052 |url=https://ieeexplore.ieee.org/document/9779481}}</ref> which shows  the term 'Harvard architecture' did not come into use until the 1970s (in the context of microcontrollers) and was only retrospectively applied to the Harvard machines, and that the term could only be applied to the [[Harvard Mark III|Mark III]] and [[Harvard Mark IV|IV]], not to the Mark I or [[Harvard Mark II|II]].{{Cn|date=March 2025}}

The main sequence mechanism was unidirectional. This meant that complex programs had to be physically lengthy. A program loop was accomplished by [[loop unrolling]] or by joining the end of the paper tape containing the program back to the beginning of the tape (literally creating a [[Closed curve|loop]]). At first, [[conditional branch]]ing in Mark I was performed manually. Later modifications in 1946 introduced automatic program branching (by [[subroutine]] call).<ref>{{cite book |last1=Beyer |first1=Kurt W. |title=Grace Hopper and the Invention of the Information Age |date=2015 |publisher=BookBaby |isbn=9781483550497 |url=https://books.google.com/books?id=mp5XDQAAQBAJ&q=%22subsidiary+sequence+unit%22&pg=PT78 |language=en |pages=78–79 }}{{Dead link|date=July 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{citation |mode=cs1|last=Bloch|first=Richard|date=1984-02-22|title=Oral history interview with Richard M. Bloch|language=en-US|pages=9–10|hdl=11299/107123}}</ref><ref>{{Cite web|url=http://www.cbi.umn.edu/hostedpublications/Tomash/index.htm|title=The Erwin Tomash Library on the History of Computing: An Annotated and Illustrated Catalog|date=1948|website=www.cbi.umn.edu|series=CBI Hosted Publications|at=Image: [http://www.cbi.umn.edu/hostedpublications/Tomash/Images%20web%20site/Image%20files/H%20Images/index_5.htm Harvard.Vol 16.1948.subsiderary sequence mechanism], description: ''H Chapter'', pp. 577–578|language=en|access-date=2018-05-08}}</ref><ref>{{harvp|A Manual of Operation|1946}}: ''subsidiary sequence control'', pp. 22, 50, 57, 73, 91</ref>{{sfnp|Campbell|1999|p=53}} The first programmers of the Mark&nbsp;I were computing pioneers [[Richard Milton Bloch]], Robert Campbell, and [[Grace Hopper]].<ref>Wexelblat, Richard L. (Ed.) (1981). ''History of Programming Languages'', p. 20. New York: Academic Press. {{ISBN|0-12-745040-8}}</ref> There was also a small technical team whose assignment was to actually operate the machine; some had been IBM employees before being required to join the Navy to work on the machine.<ref>{{cite book|url=https://books.google.com/books?id=KKmiw-_2gYIC|last=Williams|first=Kathleen|title=Grace Hopper: Admiral of the Cyber Sea|publisher=Naval Institute Press|date=2012|pages=33–34|access-date=August 7, 2019|isbn=9781612512655}}</ref> This technical team was not informed of the overall purpose of their work while at Harvard.{{Cn|date=March 2025}}

<gallery mode="packed">
File:Harvard Mark I card punch.agr.jpg|Card punch used to prepare programs
File:Harvard Mark I program tape.agr.jpg|Program tape with visible [[Patch (computing)|programming patches]]
File:Harvard Mark I constant switches detail.jpg|Rotary switches used to enter program data constants
File:IBM Automatic Sequence Controlled Calculator Sequence Indicators.jpg|Sequence indicators and switches
File:Harvard Mark I rear.JPG|Rear view of the computing section
</gallery>

==Instruction format==
The 24 channels of the input tape were divided into three fields of eight channels each. Each storage location, each set of switches, and the [[Hardware register|registers]] associated with the [[Input/output|input, output]], and [[Arithmetic logic unit|arithmetic units]] were assigned a unique identifying index number. These numbers were represented in [[Binary numeral system|binary]] on the control tape. The first field was the binary index of the result of the operation, the second was the source [[datum]] for the operation and the third field was a [[Opcode|code]] for the [[Instruction (computer science)|operation]] to be performed.<ref name="wilkes">{{cite book
  |author = Maurice Vincent Wilkes
  |title = Automatic Digital Computers
  |publisher = John Wiley & Sons
  |year = 1956
  |location = New York
  |pages = 16–20<!--   305 pages that's total, not the ones we want -->
  |url = https://books.google.com/books?id=n_oNAAAAQAAJ   <!-- | id = QA76.W5 1956 what is that? -->
  |author-link = Maurice Wilkes
}}</ref>

==Contribution to the Manhattan Project==
In 1928 [[Leslie Comrie|L.J. Comrie]] was the first to turn IBM "punched-card equipment to scientific use: computation of astronomical tables by the method of finite differences, as envisioned by Babbage 100 years earlier for his Difference Engine".<ref>{{cite web|url=http://www.columbia.edu/cu/computinghistory/comrie.html|title= Columbia University Computing History: L.J. Comrie|access-date=15 December 2013}}</ref> Very soon after, IBM  started to modify its tabulators to facilitate this kind of computation.  One of these tabulators, built in 1931, was The Columbia Difference Tabulator.<ref>{{cite web|url=http://www.columbia.edu/cu/computinghistory/packard.html|title=The Columbia Difference Tabulator – 1931|access-date=15 December 2013}}</ref>

[[John von Neumann]] had a team at Los Alamos that used "modified IBM punched-card machines"<ref name=better>{{harvp|Cohen|2000|p=166}}</ref> to determine the effects of the implosion. In March 1944, he proposed to run certain problems regarding implosion on the Mark I, and he arrived at Harvard together with two mathematicians to write a simulation program to study the implosion of the first [[atomic bomb]].{{sfnp|Cohen|2000|p=164}}

<blockquote>The Los Alamos group completed its work in a much shorter time than the Cambridge group.  However, the punched-card machine operation computed values to six decimal places, whereas the Mark I computed values to eighteen decimal places. Additionally, Mark I integrated the partial differential equation at a much smaller interval size [or smaller mesh] and so...achieved far greater precision.<ref name=better /></blockquote>

"Von Neumann joined the [[Manhattan Project]] in 1943, working on the immense number of calculations needed to build the atomic bomb. He showed that the implosion design, which would later be used in the [[Trinity (nuclear test)|Trinity]] and [[Fat Man]] bombs, was likely faster and more efficient than the gun design."<ref>{{cite web|url=https://www.atomicheritage.org/profile/john-von-neumann |title=Atomic Heritage Foundation: John von Neumann|access-date=12 May 2019}}</ref>

==Aiken and IBM==
Aiken published a press release announcing the Mark I listing himself as the sole inventor. [[James W. Bryce]] was the only IBM person mentioned, even though several IBM engineers including Clair Lake and Frank Hamilton had helped to build various elements. IBM chairman [[Thomas J. Watson]] was enraged, and only reluctantly attended the dedication ceremony on August 7, 1944.<ref name="pugh">{{cite book |author= Emerson W. Pugh |title= Building IBM: Shaping an Industry and Its Technology |publisher= MIT Press |year= 1995 |isbn= 978-0-262-16147-3 |url = https://books.google.com/books?id=Bc8BGhSOawgC }}</ref><ref>{{cite book  |author1= Martin Campbell-Kelly |author2 = William Aspray |title = Computer: A History of the Information Machine |publisher = [[Basic Books]] |year = 1996 |isbn = 0-465-02989-2 |page=74|author1-link = Martin Campbell-Kelly |title-link = Computer: A History of the Information Machine }}</ref> Aiken, in turn, decided to build further machines without IBM's help, and the ASCC came to be generally known as the "Harvard Mark I". IBM went on to build its [[IBM SSEC|Selective Sequence Electronic Calculator]] (SSEC) to both test new technology and provide more publicity for the company's efforts.<ref name="pugh"/>

==Successors==
The Mark I was followed by the [[Harvard Mark II]] (1947 or 1948), [[Harvard Mark III|Mark III/ADEC]] (September 1949), and [[Harvard Mark IV]] (1952) – all the work of Aiken. The Mark II was an improvement over the Mark I, although it still was based on electromechanical [[relay]]s. The Mark III used mostly [[electronic component]]s—[[vacuum tube]]s and [[crystal diode]]s—but also included mechanical components: rotating [[Drum memory|magnetic drums]] for storage, plus relays for transferring data between drums. The Mark IV was all-electronic, replacing the remaining mechanical components with [[magnetic core memory]]. The Mark II and Mark III were delivered to the [[United States Navy|US Navy]] base at [[Dahlgren, Virginia]]. The Mark IV was built for the [[United States Air Force|US Air Force]], but it stayed at Harvard.{{Citation needed|date=August 2019}}

The Mark I was disassembled in 1959, and portions of it went on display  in the [[Harvard Science Center|Science Center]], as part of the [[Harvard Collection of Historical Scientific Instruments]].  It was relocated to the new [[Harvard John A. Paulson School of Engineering and Applied Sciences|Science and Engineering Complex]] in [[Allston]] in July 2021.<ref name="Mark1Rebooted">{{cite web |last=Powell |first=Alvin |url=https://www.seas.harvard.edu/news/2021/07/mark-1-rebooted |website=Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) |title= Mark 1, rebooted |location=Cambridge, Massachusetts |publisher=President and Fellows of Harvard College |access-date=2021-07-28}}</ref> Other sections of the original machine had much earlier been transferred to IBM and the [[Smithsonian Institution]].<ref name="AtlasObs">{{cite web|title=Collection of Historical Scientific Instruments Mark I|url=http://www.atlasobscura.com/places/mark-i|website=Atlas Obscura|access-date=2016-05-24}}</ref>

==See also==
* [[Difference engine]] – a pioneering 19th-century mechanical computer 
* [[History of computing hardware]]
* [[:Category:Electro-mechanical_computers|List of electromechanical computers]]
* [[List of vacuum-tube computers]]

==References==
{{Reflist|colwidth=30em}}
;Publications
{{refbegin}}
* {{cite book | editor-last = Cohen| editor-first = Bernard| year = 1999| title = Makin' Numbers | publisher=The MIT Press | location= Cambridge, Massachusetts|isbn= 0-262-03263-5 }}
* {{cite book | last = Cohen| first = Bernard| year = 2000| title = Howard Aiken, Portrait of a computer pioneer  | publisher=The MIT Press | location= Cambridge, Massachusetts|isbn= 978-0-2625317-9-5 }}
* {{Citation | last = Campbell | first = Robert | author-link = Robert Campbell (journalist) | title = Aiken's First Machine | year = 1999 }} in {{Harvp|Cohen|1999|pp=31–63}} 
* {{Cite journal |ref={{harvid|A Manual of Operation|1946}} |author=Harvard Computation Laboratory |title=A Manual of Operation for the Automatic Sequence Controlled Calculator |journal=In: The Annals of the Computation Laboratory of Harvard University: Volume I |place=Cambridge, Massachusetts |publisher=Harvard University Press |year=1946 |volume=158 |issue=4017 |page=567 |doi=10.1038/158567a0 |bibcode=1946Natur.158..567C |url=http://www.bitsavers.org/pdf/harvard/MarkI_operMan_1946.pdf}}
{{refend}}

==Further reading==
{{refbegin}}
* {{Citation | last = Copeland | first = Jack | author-link = Jack Copeland | chapter = Machine against Machine | pages = 64–77 | year = 2006 | editor-last = Copeland | editor-first = B. Jack | editor-link = Jack Copeland | title = Colossus: The Secrets of Bletchley Park's Codebreaking Computers | place = Oxford | publisher = Oxford University Press | isbn = 978-0-19-284055-4 |ref=none}}
* {{cite book |last=Cruz |first=Frank da |chapter=The IBM Automatic Sequence Controlled Calculator |via=Columbia University Computing History (August 2004) |chapter-url=http://www.columbia.edu/acis/history/mark1.html |editor-last=Grosch |editor-first=Herbert R. J. |title=Computer: Bit Slices From a Life |year=1991 |publisher=Third Millennium Books |isbn=0-88733-085-1 |url=http://www.columbia.edu/acis/history/computer.html}}
* {{cite magazine |url=https://books.google.com/books?id=PyEDAAAAMBAJ&pg=PA86 |title=Robot Mathematician Knows All the Answers |author=Popular Science |magazine=Popular Science |date=October 1944 |pages=86ff |ref=none}}
* {{Cite book | last = Zuse| first = Konrad | title = The Computer: My life | year = 1993 | publisher = Pringler-Verlag | location = Berlin | isbn = 0-387-56453-5 |ref=none}}
{{refend}}

==External links==
* [http://purl.umn.edu/107348 Oral history interview with Robert Hawkins] at [[Charles Babbage Institute]], University of Minnesota, Minneapolis.  Hawkins discusses the Harvard-IBM Mark I project that he worked on at Harvard University as a technician as well as [[Howard Aiken]]’s leadership of the project.
* [http://purl.umn.edu/107123 Oral history interview with Richard M. Bloch] at [[Charles Babbage Institute]], University of Minnesota, Minneapolis.  Bloch describes his work at the Harvard Computation Laboratory for [[Howard Aiken]] on the Mark I.
* [http://purl.umn.edu/107210 Oral history interview with Robert V. D. Campbell] at [[Charles Babbage Institute]], University of Minnesota, Minneapolis.  Campbell discusses the contributions of Harvard and IBM to the Mark I project.
* Photo with parts of the machine identified: {{cite web |title=IBM ASCC-Mark I computer framed photograph {{!}} Objects {{!}} The Collection of Historical Scientific Instruments |url=http://waywiser.rc.fas.harvard.edu/objects/20051/ibm-asccmark-i-computer-framed-photograph |website=waywiser.rc.fas.harvard.edu |language=en |access-date=November 4, 2018 |archive-date=August 1, 2020 |archive-url=https://web.archive.org/web/20200801154252/http://waywiser.rc.fas.harvard.edu/objects/20051/ibm-asccmark-i-computer-framed-photograph |url-status=dead }}
* [http://www-1.ibm.com/ibm/history/exhibits/markI/markI_reference.html IBM Archive: IBM ASCC Reference Room]

{{Mainframes}}
{{authority control}}

[[Category:IBM computers]]
[[Category:Electro-mechanical computers]]
[[Category:One-of-a-kind computers]]
[[Category:Programmable calculators]]
[[Category:1940s computers]]
[[Category:Computer-related introductions in 1944]]
[[Category:Harvard University]]
[[Category:Norman Bel Geddes]]