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Unix - Wikipedia
Introduction to UNIX System - GeeksforGeeks
What Is Unix, and Why Does It Matter? - How-To Geek
UNIX | Definition, Meaning, History, & Facts | Britannica
What is UNIX
History of Unix - Wikipedia
An Introduction to the Unix Command Line - Stanford University
A Brief History of Unix - How-To Geek
What is Unix? - TechTarget
The UNIX System -- The Single UNIX Specification