A 21-year-old in Helsinki wrote a task-switcher that made one process print A's and another print B's, just to prove they could share a screen — the operating system it grew into now runs every one of the world's 500 fastest supercomputers.

Linus Torvalds set out to prove that two pieces of software could take turns using a screen without stepping on each other. He was not trying to build an operating system.

The machine he tested it on was an IBM-compatible 386, bought new in January 1991 for about 18,000 Finnish markka, paid off in installments funded partly by a student loan. He was a second-year computer science student at the University of Helsinki at the time, and the routine he wrote had two processes: one wrote the letter A to the terminal in a loop, the other wrote B. Nothing else. If the machine could hand control back and forth between them without garbling the output, he had a working task switcher: the seed a kernel grows from.

What was Linux originally called?

Freax.

Torvalds's working name mashed together "free," "freak," and the X that signaled a Unix-alike, and he used it for the earliest tarballs he put together that year. He did not get to keep it. Ari Lemmke, a research assistant who administered the FTP server at the Helsinki University of Technology where Torvalds wanted to host the code, thought Freax was a bad name and created a directory called "linux" instead, without asking first. Torvalds later said he considered the name too self-important to have chosen it himself; he adopted it anyway once Lemmke had already made the decision for him.

The code went up on that server, ftp.funet.fi, and from there onto Usenet, the sprawling, newsgroup-based precursor to today's web forums, still very much alive among university users in 1991.

The announcement that undersold itself

On August 25, 1991, Torvalds posted to comp.os.minix under the subject line "What would you like to see most in minix?" MINIX was Andrew Tanenbaum's teaching operating system, small enough to study, and Torvalds had been using it to write and test his own kernel before it could stand on its own. His post described the project as free, built for 386- and 486-class AT clones, and, in his words, "just a hobby, won't be big and professional like gnu." He asked what features people wanted and promised nothing: "I won't promise I'll implement them."

GNU was Richard Stallman's project, already years old and aimed at a complete free Unix-like system; it had the compiler and the tools but, in 1991, no finished kernel of its own. Torvalds's message read less like a launch than a request for help with a side project, which is roughly what it was. Version 0.01 followed on September 17: about 10,000 lines, not even independently compilable, needing MINIX itself to build and test it. It was not publicly announced. People simply noticed the file on the server and started downloading it.

Growth after that point is reasonably well documented, though the exact headcount of early contributors is not: within a year the kernel had picked up outside patches, a mailing list, and enough momentum that Torvalds was managing contributions rather than writing all of it himself. By 1994 there was a 1.0 release; by the late 1990s companies were shipping it.

Where did the penguin come from?

A zoo bite in Canberra.

In 1993, on a visit to Australia, Torvalds was nipped on the finger by a small penguin at what is now the National Zoo & Aquarium (by his own account a mild nibble, not a wound, from a bird investigating whether his finger was food). He started joking afterward that he had come down with "penguinitis," an invented affliction that left him unable to stop thinking about the animals. When the kernel-development mailing list took up the question of a logo in early 1996, after proposals for eagles and other conventionally fierce mascots, Torvalds said what he actually wanted was a penguin: contented-looking, sitting down, not aggressive. Artist Larry Ewing produced the design in GIMP, released it into the public domain, and the naming (Tux, generally read as a contraction of "Torvalds UniX") followed from the community rather than from Torvalds himself. The zoo in Canberra later put up a small plaque noting the connection.

Does anyone still use the original code?

Not directly; Linux has been rewritten, extended, and ported so many times since 1991 that almost none of the original 10,000 lines survive unmodified in a current kernel tree. What survived is the model: a kernel developed in the open, licensed under the GNU General Public License so that anyone could copy, study, and redistribute it, with patches submitted by volunteers and reviewed by a maintainer hierarchy that Torvalds still sits atop. That model is why a hobby project from a Helsinki dorm room scaled past anything its author predicted for it — not because the code was flawless, but because nobody had to ask permission to fix it.

The reach by now is not really in dispute. Every current Android phone runs a modified Linux kernel underneath its own application layer; a large majority of the busiest web servers run Linux directly; and for close to a decade running, the TOP500 list of the world's fastest supercomputers has been Linux at the top, middle, and bottom of the ranking, every single machine on it. None of that was the point of the original assignment Torvalds set himself, which was only ever to get one process to yield cleanly to another and prove the swap actually worked. The kernel that resulted from it is still, at its core, doing exactly that — deciding, thousands of times a second, whose turn it is next.

Sources

• Wikipedia, "History of Linux"
• Wikipedia, "Linus Torvalds"
• Wikipedia, "Tux (mascot)"
• LWN.net, "What would you like to see most in minix?" (reproduction of Linus Torvalds's original August 25, 1991 Usenet post)
• Computernewb Wiki, "Linux 0.01"
• Linux Foundation, "Linux Runs All of the World's Fastest Supercomputers"