At the urging of John Shaw Billings, Hollerith developed a mechanism using electrical connections to trigger a counter, recording information. A key idea was that data could be encoded by the locations of holes in a card. Hollerith determined that data punched in specified locations on a card, in the now-familiar rows and columns, could be counted or sorted mechanically. A description of this system, An Electric Tabulating System (1889), was submitted by Hollerith to Columbia University as his doctoral thesis, and is reprinted in Randell's book. On January 8, 1889, Hollerith was issued U.S. Patent 395,782, claim 2 of which reads:
Hollerith tabulating machine with sorting box.
The herein-described method of compiling statistics, which consists in recording separate statistical items pertaining to the individual by holes or combinations of holes punched in sheets of electrically non-conducting material, and bearing a specific relation to each other and to a standard, and then counting or tallying such statistical items separately or in combination by means of mechanical counters operated by electro-magnets the circuits through which are controlled by the perforated sheets, substantially as and for the purpose set forth.
Hollerith had left teaching and begun working for the United States Census Bureau in the year he filed his first patent application. Titled "Art of Compiling Statistics", it was filed on September 23, 1884; U.S. Patent 395,782 was granted on January 8, 1889.
Hollerith initially did business under his own name, as The Hollerith Electric Tabulating System, specializing in punched card data processing equipment. He built tabulators and other machines under contract for the Census Office, which used them for the 1890 census. The net effect of the many changes from the 1880 census: the larger population, the data items to be collected, the Census Bureau headcount, the scheduled publications, and the use of Hollerith's electromechanical tabulators, was to reduce the time required to process the census from eight years for the 1880 census to six years for the 1890 census.
In 1896 Hollerith founded the Tabulating Machine Company (in 1905 renamed The Tabulating Machine Company). Many major census bureaus around the world leased his equipment and purchased his cards, as did major insurance companies. Hollerith's machines were used for censuses in England, Italy, Germany, Russia, Austria, Canada, France, Norway, Puerto Rico, Cuba, and the Philippines, and again in the 1900 census.
To improve his system, he invented the first automatic card-feed mechanism and the first keypunch (that is, a punch operated by a keyboard); a skilled operator could punch 200–300 cards per hour. The 1890 Tabulator was hardwired to operate on 1890 Census cards. A control panel in his 1906 Type I Tabulator simplified rewiring for different jobs. The 1920s removeable control panel supported prewiring and near instant job changing. These inventions were among the foundations of the data processing industry and Hollerith's punched cards (later used for computer input/output) continued in use for almost a century.
Hollerith is buried at Oak Hill Cemetery in the Georgetown neighborhood of Washington, D.C., as is his son, Herman Hollerith Jr.
Hollerith cards were named after the elder Herman Hollerith, as were Hollerith constants (also sometimes called Hollerith strings), an early type of string constant declaration (in computer programming).
^O'Connor, J.J.; Robertson, E.F. "Herman Hollerith". The MacTutor History of Mathematics Archive. School of Mathematics and Statistics, University of St Andrews, Scotland. Retrieved 5 March 2013.
^Lydenberg, Harry Miller (1924). John Shaw Billings: Creator of the National Medical Library and its Catalogue, First Director of the New York Public Library. American Library Association. p. 32.
^Randell (ed.), Brian (1982). The Origins of Digital Computers, Selected Papers (3rd ed.). Springer-Verlag. ISBN0-387-11319-3.
^US patent 395782, Herman Hollerith, "Art of compiling statistics", issued 1889-01-08
^The "sorting box" was controlled by the tabulator. The "sorter", an independent machine, was a later development.Austrian, Geoffrey D. (1982). Herman Hollerith: Forgotten Giant of Information Processing. Columbia University Press. pp. 41, 178–179. ISBN0-231-05146-8.
^Report of the Commissioner of Labor In Charge of The Eleventh Census to the Secretary of the Interior for the Fiscal Year Ending June 30, 1895 Washington, D.C., July 29 1895 Page 9: You may confidently look for the rapid reduction of the force of this office after the 1st of October, and the entire cessation of clerical work during the present calendar year. ... The condition of the work of the Census Division and the condition of the final reports show clearly that the work of the Eleventh Census will be completed at least two years earlier than was the work of the Tenth Census. Carroll D. Wright Commissioner of Labor in Charge.
^"IBM Archives: Frequently Asked Questions"(PDF). Some accounts of the consolidation forming CTR state that only three corporations were included. This reference notes that only three of the four corporations are represented in the CTR name. That may be the reason for the differing accounts.
Cortada, James W. (1993). Before the Computer: IBM, NCR, Burroughs, & Remington Rand & the Industry they created, 1865 - 1956. Princeton. p. 344. ISBN0-691-04807-X.
Essinger, James (2004). Jacquard's Web: How a Hand-Loom Led to the Birth of the Information Age. Oxford: Oxford University Press.
Heide, Lars (2009). Punched-Card Systems and the Early Information Explosion, 1880-1945. Johns Hopkins. ISBN0-8018-9143-4.
Hollerith, Herman (April 1889). "An Electric Tabulating System". The Quarterly, Columbia University School of Mines. X (16): 238–255. From the Columbia Univ. History site: This article is the basis for his 1890 Columbia Ph.D. Extracts reprinted in (Randell, 1982).
Hollerith, Herman (1890). In connection with the electric tabulation system which has been adopted by U.S. government for the work of the census bureau. Ph.D. dissertation. Columbia University School of Mines.
Hollerith, Herman (December 1894). "The Electrical Tabulating Machine". Journal of the Royal Statistical Society. Blackwell Publishing. 57 (4): 678–682. doi:10.2307/2979610. JSTOR2979610. From Randell (1982),"... brief... fascinating article... describes the way in which tabulators and sorters were used on ... 100 million cards ... 1890 census."
Truedsell, Leon E. (1965). The Development of Punch Card Tabulation in the Bureau of the Census 1890-1940. US GPO. Includes extensive, detailed, description of Hollerith's first machines and their use for the 1890 census.
Richard Hollerith Papers at Hagley Museum and Library. Richard Hollerith was the grandson of Herman Hollerith and part of this collection documents the sale and settlement of the Herman Hollerith estate following the death of his last remaining child, Virginia.