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Grace Brewster Murray Hopper (1906–1992) was an American computer scientist, mathematician, and United States Navy rear admiral. Her career spanned more than four decades of active service and pioneering software development, during which she fundamentally changed how programmers interact with computers.

## Early Life and Education

Hopper was born in New York City on 9 December 1906. She earned a bachelor's degree in mathematics and physics from Vassar College in 1928, followed by a master's degree and a doctorate in mathematics from Yale University in 1934. She was among the few women in the United States to hold a doctorate in mathematics at the time. She taught mathematics at Vassar from 1931 until she joined the Navy during the Second World War.

## Naval Service

Hopper enlisted in the United States Navy Reserve in 1943, receiving a commission as a lieutenant junior grade. She was assigned to the Bureau of Ships Computation Project at Harvard University, where she worked with Commander Howard Aiken on the Harvard Mark I, one of the earliest large-scale electromechanical computers. The Mark I was 51 feet long and performed arithmetic by reading instructions punched on paper tape.

Hopper's work on the Mark I and its successors — the Mark II and Mark III — gave her deep familiarity with how computers executed instructions and where they failed. It was during work on the Mark II in 1947 that her team discovered a moth lodged in a relay, causing a malfunction. They taped the moth into the logbook with the annotation "first actual case of bug being found," providing the literal origin of the now-universal term debugging.

## The A-0 System and the Compiler Concept

After the war Hopper joined the Eckert-Mauchly Computer Corporation, where she worked on the UNIVAC I, one of the first commercial computers sold in the United States. The UNIVAC I became famous in 1952 when CBS used it to predict the outcome of the presidential election on live television.

At Eckert-Mauchly (later absorbed by Remington Rand), Hopper developed what she called the A-0 system in 1952. The A-0 was a program that translated a set of symbolic mathematical notations into machine instructions by retrieving previously written subroutines from a library. She described this as a compiler — a program that compiles subroutines into a running program.

The idea was controversial. Her colleagues and managers were sceptical that a computer could be trusted to produce correct machine code automatically; programming was considered an activity requiring direct human control at the instruction level. Hopper persisted, arguing that the computer's value lay precisely in automating repetitive, error-prone work. Subsequent versions — the A-1 and A-2 compilers — refined the approach. The debate over whether A-0 constitutes a true compiler in the modern sense (as opposed to a linker or loader) continues among historians, but Hopper's conceptual contribution — that translation from human-readable notation to machine instructions could be mechanised — was unambiguous and transformative.

## COBOL

In 1959, Hopper was instrumental in the design of COBOL (Common Business-Oriented Language). The language emerged from a meeting convened by the United States Department of Defense, which sought a common programming language for business data processing that could run on different manufacturers' computers.

Hopper championed English-like syntax in the new language, arguing that programs written in recognisable words — READ, WRITE, COMPUTE — would be readable by business managers and auditors, not only by programmers. COBOL was standardised in 1960 and rapidly became the dominant language for business applications. Financial institutions, insurance companies, and government agencies adopted COBOL for payroll, billing, and record-keeping systems. Large bodies of COBOL code were still running in production decades after the language's introduction.

## Naval Career and Retirement

Hopper's naval career extended far beyond the wartime assignment that began it. She was recalled to active duty multiple times and eventually achieved the rank of rear admiral in 1985, the highest rank achieved by a woman in the United States Navy to that point. She retired from active duty in 1986 at the age of 79, the oldest serving officer on active duty in the Navy.

She was awarded the National Medal of Technology in 1991 and the Presidential Medal of Freedom posthumously in 2016.

## Legacy

Hopper's enduring contribution was insisting that computers should serve human language, not the reverse. This principle — that programming notation should be readable and portable across hardware — underlies every high-level language developed since the 1950s. The Grace Hopper Celebration of Women in Computing, first held in 1994, is the world's largest gathering of women technologists and bears her name.

The USS Hopper, a guided-missile destroyer commissioned in 1997, was named in her honour.
