Ken Thompson

Ken Thompson: The Quiet Architect of Everything

When Bell Labs pulled out of the Multics project in 1969, Ken Thompson was left with an obsolete PDP-7 minicomputer in a corner and no official mandate. He used it to build an operating system anyway. Unix now runs, in some descendant form, on nearly every server, phone and embedded device on the planet. Dennis Ritchie, Thompson's closest collaborator and no small figure himself, said of that first version that "most of the ideas, and most of the work for that matter, were his."

Arithmetic in Binary

Kenneth Lane Thompson was born on 4 February 1943 in New Orleans, Louisiana. His account of his own childhood is characteristically unadorned: "I was always fascinated with logic and even in grade school I'd work on arithmetic problems in binary, stuff like that. Just because I was fascinated." That last clause is the whole man — an intellectual appetite with no instrumental purpose attached to it.

He took a bachelor's degree in 1965 and a master's in 1966, both in electrical engineering and computer sciences, from the University of California, Berkeley, where his thesis advisor was the coding theorist Elwyn Berlekamp. Bell Laboratories hired him in 1966 into the Computing Sciences Research Center at Murray Hill, New Jersey.

Unix

Between 1967 and 1969 Thompson worked on Multics, the ambitious joint timesharing project between Bell Labs, MIT and General Electric. Multics was enormous, slow and late; Bell Labs withdrew. What Thompson took from it was a conviction that the ideas were right and the execution was wrong.

The origin story is well attested and slightly absurd. He wanted to keep playing Space Travel, a game he had written, and he wanted a decent environment to work in. On a cast-off PDP-7, with minimal resources and no institutional support, he built the core of an operating system: a hierarchical file system, processes, device files treated as ordinary files, a command-line interpreter separate from the kernel, and pipes for chaining programs together. Each of those is now so standard that it takes effort to see them as choices.

The design philosophy was compression. Rather than a system that anticipated every need, Unix offered a small number of composable primitives and let users assemble what they wanted. By 1973 more than twenty installations existed. To write the non-kernel parts more easily, Thompson created the B programming language, derived from BCPL, which Ritchie then developed into C — the language in which most of the world's infrastructure software is still written.

Small Tools, Deep Roots

Thompson's other work has the same signature: a compact idea that turns out to be load-bearing. He implemented regular expressions in the QED and ed editors and devised Thompson's construction, the algorithm for converting a regular expression into a finite automaton. Nearly every regular expression engine in use today is a descendant of that notation.

He built a chess program in 1971, then with Joseph Condon built Belle, a special-purpose chess machine that dominated computer chess in its era, and afterwards generated the complete endgame tablebases for four-, five- and six-piece endings — exhaustive solutions to entire classes of chess position, a body of work that permanently changed the theory of the endgame.

In 1992, with Rob Pike, he designed UTF-8, the character encoding that lets a single byte stream carry any script on Earth while remaining compatible with ASCII. It now accounts for more than 90 per cent of the web. He was also central to Plan 9, the distributed operating system Bell Labs built in the mid-1980s to push the Unix ideas further than Unix itself could go.

His 1983 Turing lecture, "Reflections on Trusting Trust," described a compiler that inserts a backdoor into programs it compiles, and also into future versions of itself, so that the malicious code appears nowhere in any source anyone can read. The Thompson hack is a foundational document of computer security; the source was annotated and published in 2023.

Google, and Go

Thompson retired from Bell Labs in late 2000 and joined Google in 2006, where with Rob Pike and Robert Griesemer he designed the Go programming language. His account of the motivation is blunt: "The three of us got together and decided that we hated C++," a language he has called "a garbage heap of ideas that are mutually exclusive." Go was built on the rule that all three designers had to be persuaded of every feature, which is a discipline for keeping a language small.

The honours accumulated steadily: election to the National Academy of Engineering in 1980, the IEEE Emanuel R. Piore Award in 1982, the ACM Turing Award with Ritchie in 1983, the National Academy of Sciences in 1985, the IEEE Richard W. Hamming Medal in 1990, the Computer Pioneer Award in 1994, a Computer History Museum fellowship in 1997, the National Medal of Technology in 1998, the inaugural Tsutomu Kanai Award in 1999 and the Japan Prize for Information and Communications in 2011.

Why Ken Is Called a Genius

The ACM's Turing citation makes an unusually precise claim, and it is worth quoting because it locates the quality exactly: "The success of the UNIX system stems from its tasteful selection of a few key ideas and their elegant implementation... The genius of the Unix system is its framework, which enables programmers to stand on the work of others."

Taste is the operative word. Thompson's talent is subtractive — an ability to identify the smallest set of concepts that will generate the largest space of useful behaviour, and then refuse everything else. Pipes are the canonical example: a trivial mechanism for connecting the output of one program to the input of another, which turns a collection of small tools into a combinatorial system. Regular expressions, UTF-8 and Go all show the same pattern of minimum sufficient design. He is routinely named among the greatest programmers who have ever lived, and the judgement comes from people who write code for a living rather than from prize committees.

The counter-case is thinner than for most on this list but exists. Unix was collaborative — Ritchie, Brian Kernighan, Douglas McIlroy, who proposed pipes, and others shaped it profoundly, and the Turing Award was shared. Many Unix ideas were adapted from Multics rather than invented fresh. Thompson has produced no theoretical result in computer science, and his influence is entirely in artefacts and design judgement. Whether that constitutes genius or an extraordinarily well-developed craft is a fair question. The most honest answer is that in software the two are difficult to separate, and Thompson's craft has proved more consequential than most people's theories.

Legacy

Linux, macOS, Android, iOS and the software running virtually every internet server descend from decisions Thompson made alone on a discarded machine in 1969. His character encoding carries almost all written text online. His regular expression algorithm sits inside every text editor. He recorded a long oral history for the Computer History Museum in 2024, and has spent his later years, having abandoned Apple's products, running Raspberry Pi OS.

Achievements

• Turing Award — 1983
• National Medal of Technology and Innovation — 1998
• Notable work: Belle
• Notable work: Go
• Notable work: Plan 9
• Notable work: Multics
• Affiliated with Bell Labs and Google
• Educated at University of California, Berkeley and University of California, Berkeley
• Worked as programmer and computer scientist