How did Ken Thompson write the first version of Unix in three weeks?

According to Brian Kernighan, Ken Thompson had been experimenting with disk scheduling on an obsolete PDP-7 with about 8K 18-bit words of memory. When his wife took their young son to California for three weeks in 1969, he used the time to write an editor, an assembler and an operating system by himself. Kernighan believes he wrote it in assembly, probably edited the code on another machine that had a text editor, and carried paper tapes over to load onto the PDP-7.

• Kernighan stressed that none of today's online resources, such as Stack Overflow, existed in 1969.
• Kernighan's explanation for how Thompson managed it was simply that he is far smarter than most people.

Source: our own transcription of the episode. The full conversation is on Ryan Peterman (2026-11-05). Read the whole episode summary →

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