The Harvard Mark I, or IBM Automatic Sequence Controlled Calculator (ASCC), was a general-purpose electromechanical

computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations ( computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These prog ...

used in the war effort during the last part of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

. One of the first programs to run on the Mark I was initiated on 29 March 1944 by

John von Neumann John von Neumann (; hu, Neumann János Lajos, ; December 28, 1903 – February 8, 1957) was a Hungarian-American mathematician, physicist, computer scientist, engineer and polymath. He was regarded as having perhaps the widest c ...

. At that time, von Neumann was working on the

Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...

, and needed to determine whether 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 Charles Babbage (; 26 December 1791 – 18 October 1871) was an English polymath. A mathematician, philosopher, inventor and mechanical engineer, Babbage originated the concept of a digital programmable computer. Babbage is considered ...

for his "

analytical engine The Analytical Engine was a proposed mechanical general-purpose computer designed by English mathematician and computer pioneer Charles Babbage. It was first described in 1837 as the successor to Babbage's difference engine, which was a desig ...

" in 1837. The Mark I was disassembled in 1959, but portions of it were displayed in the Science Center as part of the

Harvard Collection of Historical Scientific Instruments Harvard University's Collection of Historical Scientific Instruments (CHSI), established 1948, is "one of the three largest university collections of its kind in the world". Waywiser, the online catalog of the collection, lists over 60% of the co ...

until being moved to the new Science and Engineering Complex in

Allston, Massachusetts Allston is an officially recognized neighborhood within the City of Boston, Massachusetts, United States. It was named after the American painter and poet Washington Allston. It comprises the land covered by the zip code 02134. For the most part ...

in July 2021. Other sections of the original machine had much earlier been transferred to IBM and the

Smithsonian Institution The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums and education and research centers, the largest such complex in the world, created by the U.S. government "for the increase and diffusion of knowledge". Found ...

Origins

The original concept was presented to IBM by Howard Aiken in November 1937. After a feasibility study by IBM engineers, the company chairman 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, he was shown a demonstration set that

’s son had given to Harvard University 70 years earlier. This led him to study Babbage and to add references of the

Analytical Engine The Analytical Engine was a proposed mechanical general-purpose computer designed by English mathematician and computer pioneer Charles Babbage. It was first described in 1837 as the successor to Babbage's difference engine, which was a desig ...

to his proposal; the resulting machine "brought Babbage’s principles of the Analytical Engine almost to full realization, while adding important new features." The ASCC was developed and built by IBM at their Endicott plant and shipped to Harvard in February 1944. It began computations for the U.S. Navy Bureau of Ships in May and was officially presented to the university on August 7, 1944.

Design and construction

The ASCC was built from switches,

relay A relay Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off A relay is an electrically operated switch ...

s, rotating shafts, and clutches. It used 765,000 electromechanical components and hundreds of miles of wire, comprising a volume of – in length, in height, and deep. It weighed about . The basic calculating units had to be synchronized and powered mechanically, so they were operated by a

drive shaft A drive shaft, driveshaft, driving shaft, tailshaft ( Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power and torque and rotation, usually used to conne ...

coupled to a electric motor, which served as the main power source and system clock. From the IBM Archives:

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 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.

The enclosure for the Mark I was designed by futuristic American

industrial designer Industrial design is a process of design applied to physical products that are to be manufactured by mass production. It is the creative act of determining and defining a product's form and features, which takes place in advance of the manufact ...

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.

Operation

The Mark I had 60 sets of 24 switches for manual data entry and could store 72 numbers, each 23 decimal digits long. 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. The Mark I read its instructions from a 24-channel

punched paper tape Five- and eight-hole punched paper tape Paper tape reader on the Harwell computer with a small piece of five-hole tape connected in a circle – creating a physical program loop Punched tape or perforated paper tape is a form of data storage ...

. It executed the current instruction and then read in 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. This separation of data and instructions is known as the

Harvard architecture The Harvard architecture is a computer architecture with separate storage and signal pathways for instructions and data. It contrasts with the von Neumann architecture, where program instructions and data share the same memory and pathway ...

(although the exact nature of this separation that makes a machine Harvard, rather than Von Neumann, has been obscured with the passage of time; see Modified Harvard architecture). 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

loop Loop or LOOP may refer to: Brands and enterprises * Loop (mobile), a Bulgarian virtual network operator and co-founder of Loop Live * Loop, clothing, a company founded by Carlos Vasquez in the 1990s and worn by Digable Planets * Loop Mobile, an ...

). At first,

conditional branch A branch is an instruction in a computer program that can cause a computer to begin executing a different instruction sequence and thus deviate from its default behavior of executing instructions in order. ''Branch'' (or ''branching'', ''bran ...

ing in the Mark I was performed manually. Later modifications in 1946 introduced automatic program branching (by

subroutine In computer programming, a function or subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed. Functions may ...

call). The first programmers of the Mark I were computing pioneers Richard Milton Bloch, Robert Campbell, and Grace Hopper. 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. This technical team was not informed of the overall purpose of their work while at Harvard. File:Harvard Mark I card punch.agr.jpg, Tape punch used to prepare programs File:Harvard Mark I program tape.agr.jpg, Program tape with visible 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 computing section

Instruction format

The 24 channels of the input tape were divided into three fields of eight channels. Each storage location, each set of switches, and the registers associated with the input, output, and arithmetic units were assigned a unique identifying index number. These numbers were represented in binary on the control tape. The first field was the binary index of the result of the operation, the second was the source

datum In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted. ...

for the operation and the third field was a code for the

operation Operation or Operations may refer to: Arts, entertainment and media * ''Operation'' (game), a battery-operated board game that challenges dexterity * Operation (music), a term used in musical set theory * ''Operations'' (magazine), Multi-Man ...

to be performed.

Contribution to the Manhattan Project

In 1928 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". 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.

had a team at Los Alamos that used "modified IBM punched-card machines" #AIKEN p.166 (2000) to determine the effects of implosion. In March 1944, he proposed to run certain problems regarding implosion on the Mark I, and in 1944 he arrived with two mathematicians to write a simulation program to study the implosion of the first atomic bomb.

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 r smaller meshand so...achieved far greater precision''.

"Von Neumann joined the

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 and Fat Man bombs, was likely faster and more efficient than the gun design."

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. 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 Selective Sequence Electronic Calculator (SSEC) to both test new technology and provide more publicity for the company's own efforts.

Successors

The Mark I was followed by the Harvard Mark II (1947 or 1948), 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

s. The Mark III used mostly

electronic component An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are no ...

s—

vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as ...

s and

crystal diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode ...

s—but also included mechanical components: rotating 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

US Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

base at Dahlgren, Virginia. The Mark IV was built for the

US Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Sig ...

, but it stayed at Harvard. The Mark I was disassembled in 1959, and portions of it went on display in the Science Center, as part of the

. It was relocated to the new Science and Engineering Complex in

Allston Allston is an officially recognized neighborhood within the City of Boston, Massachusetts, United States. It was named after the American painter and poet Washington Allston. It comprises the land covered by the zip code 02134. For the most pa ...

in July 2021. Other sections of the original machine had much earlier been transferred to IBM and to the

References

;Notes ;Publications * * * in * *

External links

*
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.
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.
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.
IBM Archive: IBM ASCC Reference Room

book excerpt web page, with illustrations, by Herb Grosch, from (Third edition online in 2003)

''Popular Science'', October 1944, Page 86.
ASCC operational manual
(PDF) *Photo with parts of the machine identified: {{authority control IBM computers Electro-mechanical computers One-of-a-kind computers Programmable calculators 1940s computers Computer-related introductions in 1944 Harvard University Norman Bel Geddes