Hall of FameDennis M. Ritchie, Ken Thompson197443 min readpaperintermediate
The UNIX Time-Sharing System
Summary
The 1974 paper outlines the original UNIX operating system for the PDP‑11, detailing its hierarchical file system, device file abstraction, and rewrite in C. It demonstrates how a small, self‑contained OS could provide multi‑user time‑sharing with a simple, uniform I/O model.
- UNIX introduced a unified hierarchical file system with directories, '.' and '..' entries, and links that give files multiple names.
- Devices are represented as special files under /dev, allowing uniform file and device I/O semantics.
- The OS and its utilities were rewritten in C, enabling portability and self‑hosting on modest hardware.
- A minimal UNIX system fit in 42 KB of core memory on a PDP‑11, demonstrating low resource requirements.
Engineers building operating systems, containers, or low‑resource software benefit from understanding these core OS abstractions.
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