Dennis Ritchie

Dennis MacAlistair Ritchie (September 9, 1941 – c. October 12, 2011) was an American computer scientist.

He is best known for creating the C programming language and, with long-time colleague Ken Thompson, the Unix operating system and B programming language.

During the 1960s, Ritchie and Ken Thompson worked on the Multics operating system at Bell Labs.

Thompson then found an old PDP-7 machine and developed his own application programs and operating system from scratch, aided by Ritchie and others.

He graduated from Harvard University with degrees in physics and applied mathematics in 1963.

In 1967, Ritchie began working at the Bell Labs Computing Science Research Center.

In 1968, he defended his PhD thesis on "Computational Complexity and Program Structure" at Harvard under the supervision of Patrick C. Fischer.

However, Ritchie never officially received his PhD degree as he did not submit a bound copy of his dissertation to the Harvard library, a requirement for the degree.

In 1970, Brian Kernighan suggested the name "Unix", a pun on the name "Multics".

To supplement assembly language with a system-level programming language, Thompson created B.

Later, B was replaced by C, created by Ritchie, who continued to contribute to the development of Unix and C for many years.

During the 1970s, Ritchie collaborated with James Reeds and Robert Morris on a ciphertext-only attack on the M-209 US cipher machine that could solve messages of at least 2000–2500 letters.

Ritchie relates that, after discussions with the National Security Agency, the authors decided not to publish it, as they were told that the principle applied to machines still in use by foreign governments.

Ritchie was also involved with the development of the Plan 9 and Inferno operating systems, and the programming language Limbo.

Ritchie and Thompson were awarded the Turing Award from the ACM in 1983, the Hamming Medal from the IEEE in 1990 and the National Medal of Technology from President Bill Clinton in 1999.

In 1983, Ritchie and Thompson received the Turing Award "for their development of generic operating systems theory and specifically for the implementation of the UNIX operating system".

Ritchie's Turing Award lecture was titled "Reflections on Software Research".

As part of an AT&T restructuring in the mid-1990s, Ritchie was transferred to Lucent Technologies, where he retired in 2007 as head of System Software Research Department.

Ritchie is best known as the creator of the C programming language, one of the developers of the Unix operating system, and co-author of the book The C Programming Language; he was the 'R' in K&R (a common reference to the book's authors Kernighan and Ritchie).

Ritchie worked together with Ken Thompson, who is credited with writing the original version of Unix; one of Ritchie's most important contributions to Unix was its porting to different machines and platforms.

They were so influential on Research Unix that Doug McIlroy later wrote, "The names of Ritchie and Thompson may safely be assumed to be attached to almost everything not otherwise attributed."

Ritchie liked to emphasize that he was just one member of a group.

He suggested that many of the improvements he introduced "looked like a good thing to do" and that anyone else in the same place at the same time might have done the same thing.

Nowadays, the C language is widely used in application, operating system, and embedded system development, and its influence is seen in most modern programming languages.

C is a low-level language with constructs closely translating to the hardware's instruction set.

However, it is not tied to any particular hardware—making it easy to write programs on any machine that supports C. Moreover, C is a high-level language with constructs mapping to the application's data structures.

C influenced several other languages and derivatives, such as C++, Objective-C used by Apple, C# used by Microsoft, and Java extensively used in corporate environment and also by Android.

Ritchie and Thompson used C to write UNIX.

Unix has been influential in establishing computing concepts and principles that have been widely adopted.

In 1990, both Ritchie and Thompson received the IEEE Richard W. Hamming Medal from the Institute of Electrical and Electronics Engineers (IEEE), "for the origination of the UNIX operating system and the C programming language".

In 1997, both Ritchie and Thompson were made Fellows of the Computer History Museum, "for co-creation of the UNIX operating system, and for development of the C programming language."

In an interview from 1999, Ritchie clarified that he saw Linux and BSD operating systems as a continuation of the basis of the Unix operating system, and as derivatives of Unix:

"I think the Linux phenomenon is quite delightful, because it draws so strongly on the basis that Unix provided. Linux seems to be among the healthiest of the direct Unix derivatives, though there are also the various BSD systems as well as the more official offerings from the workstation and mainframe manufacturers."

In the same interview, he stated that he viewed Unix and Linux as "the continuation of ideas that were started by Ken and me and many others, many years ago."

Ritchie was the head of Lucent Technologies System Software Research Department when he retired in 2007.

He was the "R" in K&R C, and commonly known by his username dmr.

Dennis Ritchie was born in Bronxville, New York.

His father was Alistair E. Ritchie, a longtime Bell Labs scientist and co-author of The Design of Switching Circuits on switching circuit theory.

As a child, Dennis moved with his family to Summit, New Jersey, where he graduated from Summit High School.

In 2020, the Computer History Museum worked with Ritchie's family and Fischer's family and found a copy of the lost dissertation.