Unix
also: UNIX, Unix-like
Unix is a modular, multi-user operating system created in the 1970s at Bell Labs that established fundamental design principles like 'everything is a file' and 'do one thing well.' Linux is a Unix-like operating system that follows these principles.
Unix is the foundational operating system developed at Bell Labs by Ken Thompson and Dennis Ritchie in 1969. It introduced revolutionary concepts that shaped modern computing: the hierarchical filesystem, shell command interpreter, and philosophy of composable tools that each do one task excellently.
Key Unix principles include treating devices and data as files (allowing you to pipe output between programs like cat file.txt | grep 'pattern' | sort), separating user space from kernel space for stability, and providing a portable, standardized interface across different hardware platforms.
While true Unix systems (BSD, Solaris, macOS) are proprietary and expensive, Linux was created as a free, open-source Unix-like kernel that implements these same principles. Most modern systems you encounter—including Linux servers, macOS, and BSD systems—follow the Unix philosophy, making it the de facto standard for server and development operating systems.