The Story of C

In 1969, in a small office at Bell Telephone Laboratories in New Jersey, a programmer named Ken Thompson wanted to play a game.

The game was called Space Travel, and the only computer he could sneak it onto was a discarded PDP-7: a refrigerator-sized machine with about 9 KB of memory. To make the game playable, Ken started writing a small operating system for the PDP-7 from scratch — with help from a colleague named Dennis Ritchie. They jokingly named it UNIX, a pun on a much bigger, much more troubled OS called Multics that they had been working on.

That side project — half operating system, half playground — went on to change computing forever.

Why a new language was needed

The first version of UNIX was written entirely in assembly language for the PDP-7, then rewritten in assembly for a newer machine called the PDP-11. Each time UNIX moved to a new computer, the entire OS had to be re-translated by hand. This was painful and fragile.

Ken Thompson tried to write UNIX in an existing high-level language called B (itself derived from BCPL), but B had no notion of data types — every value was a single machine word. That made it hopeless for code that needed to deal with bytes, characters, and structures of mixed-size data, which is most of what an operating system does.

So between 1969 and 1973, Dennis Ritchie did something quietly historic. He took B, added types (int, char, float, arrays, pointers, structs), kept it small, and called the result C.

Why C succeeded where others did not

Several deliberate decisions made C uniquely well suited to its job:

1. It was small. The entire language fits on a few dozen pages. You can hold all of C in your head. Compare this to the thousand-page specifications of modern languages.
2. It mapped cleanly to hardware. A C int is "a machine word". An if becomes a compare-and-jump. A function call becomes a stack frame. You can almost always predict what assembly the compiler will produce.
3. It exposed memory. Pointers gave programmers a way to talk about addresses directly. This is dangerous, but it is also necessary for writing operating systems, drivers, and runtimes.
4. It was portable. Once a C compiler existed for a new CPU, every C program — including the UNIX operating system itself — could be moved to that CPU. Suddenly UNIX could run on machines from many different vendors.

In 1973, Ken Thompson and Dennis Ritchie rewrote the UNIX kernel in C. This was the first time anyone had written a serious operating system in a high-level language. Most experts at the time said it couldn't be done — the result, they predicted, would be too slow and too bulky. They were wrong.

How C took over the world

Because C and UNIX were designed together, the spread of one helped the spread of the other. Universities got UNIX (often free or for a nominal license fee) and trained students who then walked into industry already fluent in C. By the 1980s C was the default language for systems programming everywhere.

Today, decades later, an astonishing amount of the software you use every day is written in C — or in something built on top of C:

• Operating system kernels. Linux, the BSDs, the core of macOS (XNU), and large parts of Windows are written in C.
• Embedded systems. Microwaves, cars, pacemakers, satellites, and the firmware inside almost every electronic device.
• Language runtimes. The reference implementation of Python (CPython), the V8 JavaScript engine that powers Chrome and Node.js, the Ruby interpreter (MRI), the PHP interpreter — all written in C or C++.
• Databases. SQLite, PostgreSQL, MySQL, Redis — all C.
• Compilers. GCC and large parts of LLVM are written in C/C++.
• Network infrastructure. Web servers (nginx, Apache), TCP/IP stacks, OpenSSL, curl — all C.

When you load a web page, dozens of C programs collaborate to make that happen.

How C influenced everything that came after

Almost every popular language in use today inherits ideas — and syntax — from C:

The braces { } you see in JavaScript, Java, C#, Go, Rust, and Swift? Those came from C. The if (...) { ... } else { ... } shape? C. The for (int i = 0; i < n; i++) loop? C. The printf-style format strings? C. The way functions take typed parameters and return a value? C. The \n for newline, the == for equality, the && for logical AND — all C.

When you learn C, you are learning the grammar that the rest of the industry has been speaking — sometimes consciously, sometimes not — for fifty years.

Why learning C is worth your time

If you only want to ship a website by Friday, you should probably not learn C first. Use Python, or JavaScript, or whatever your team uses.

But if you want to understand programming itself, C is unmatched. Here is what learning C will give you that most other languages will not:

• A real mental model of memory — what a variable is, where it lives, who owns it, when it disappears.
• An understanding of what the CPU does when you write a loop, a function call, or an if statement.
• An appreciation for what your favorite "easy" language is hiding from you, and at what cost.
• The vocabulary to read systems code: kernels, drivers, cryptographic libraries, virtual machines, language runtimes.
• A baseline for picking up other systems languages — C++, Rust, Go, Zig — much faster than you otherwise would.

A short word from Dennis Ritchie

"C is quirky, flawed, and an enormous success." — Dennis M. Ritchie

He was right on all three counts. C has rough edges. Some of its defaults are dangerous. Modern languages fix many of its mistakes. But the central idea — a small, portable, low-level language that treats memory honestly — has never been seriously displaced. Fifty years later, we are still building on top of it.

In the next chapter, we'll zoom into the machine itself: what happens when a program runs. Then, finally, we'll write some code.

QuestionSelect one

Why was C originally created at Bell Labs?

To replace FORTRAN as the language of scientific computing.

To make it possible to rewrite the UNIX operating system in a portable, high-level language.

To teach programming in universities.

To compete with Microsoft Windows.

QuestionSelect one

Which of the following is not typically written in C (or a direct descendant like C++)?

The Linux kernel.

The reference Python interpreter (CPython).

The SQLite database engine.

An HTML web page.