Humanities › History & Culture Who Invented the Mark I Computer? Share Flipboard Email Print View of IBM's Harvard Mark I Automatic Sequence Controlled Calculator (ASCC) on the campus of Harvard University, 1944. PhotoQuest / Archive Photos / Getty Images History & Culture Inventions Famous Inventors Famous Inventions Patents & Trademarks Invention Timelines Computers & The Internet American History African American History African History Ancient History and Culture Asian History European History Genealogy Latin American History Medieval & Renaissance History Military History The 20th Century Women's History View More By Mary Bellis Inventions Expert Mary Bellis covered inventions and inventors for ThoughtCo for 18 years. She is known for her independent films and documentaries, including one about Alexander Graham Bell. our editorial process Mary Bellis Updated February 03, 2020 Howard Aiken and Grace Hopper designed the MARK series of computers at Harvard University beginning in 1944. The Mark I The MARK computers began with the Mark I. Imagine a giant room full of noisy, clicking metal parts, 55 feet long and eight feet high. The five-ton device contained almost 760,000 separate pieces. Used by the U.S. Navy for gunnery and ballistic calculations, the Mark I was in operation until 1959. A detailed look at the Mark I, now housed at Harvard University. Rocky Acosta / CC BY 3.0 The computer was controlled by pre-punched paper tape, and it could carry out addition, subtraction, multiplication and division functions. It could refer to previous results and had special subroutines for logarithms and trigonometric functions. It used 23 decimal place numbers. Data was stored and counted mechanically using 3,000 decimal storage wheels, 1,400 rotary dial switches and 500 miles of wire. Its electromagnetic relays classified the machine as a relay computer. All output was displayed on an electric typewriter. By today's standards, the Mark I was slow, requiring three to five seconds to accomplish a multiplication operation. Howard Aiken Howard Aiken was born in Hoboken, New Jersey in March 1900. He was an electrical engineer and physicist who first conceived of an electro-mechanical device like the Mark I in 1937. After completing his doctorate at Harvard in 1939, Aiken stayed on to continue the computer's development. IBM funded his research. Aiken headed a team of three engineers, including Grace Hopper. Howard Aiken with Mark I in 1944. Bettmann / Getty Images The Mark I was completed in 1944. Aiken completed the Mark II, an electronic computer, in 1947. He founded the Harvard Computation Laboratory that same year. He published numerous articles on electronics and switching theories and ultimately launched Aiken Industries. Aiken loved computers, but even he had no idea of their eventual widespread appeal. "Only six electronic digital computers would be required to satisfy the computing needs of the entire United States," he said in 1947. Aiken died in 1973 in St, Louis, Missouri. Grace Hopper Born in December 1906 in New York, Grace Hopper studied at Vassar College and Yale before she joined the Naval Reserve in 1943. In 1944, she started working with Aiken on the Harvard Mark I computer. Lieutenant (junior grade) Grace Hopper working at Harvard in 1946. Should would later become a rear admiral in the Navy. U.S. Department of Defense / public domain One of Hopper's lesser-known claims to fame is that she was responsible for coining the term "bug" to describe a computer fault. The original 'bug' was a moth that caused a hardware fault in the Mark II. Hopper got rid of it and fixed the problem and was the first person to "debug" a computer. A moth taped to a 1945 Mark II computer log with the entry "First actual case of bug being found.". U.S. Naval History and Heritage Command / public domain She began research for the Eckert-Mauchly Computer Corporation in 1949 where she designed an improved compiler and was part of the team which developed Flow-Matic, the first English-language data processing compiler. She invented the language APT and verified the language COBOL. Hopper was the first computer science "Man of the Year" in 1969, and she received the National Medal of Technology in 1991. She died a year later, in 1992, in Arlington, Virginia.