Conclusion

Unix is an operating system with a rich history, originating from AT&T Bell Labs in the late 1960s. It was initially proprietary, though its source code was often freely licensed to universities. A pivotal moment in its development was its rewriting in the C programming language in 1973, which significantly enhanced its portability across diverse computer platforms.

The core of Unix is its "Unix philosophy", which advocates for a modular design. This means using small, single-purpose tools that work together by handling text streams and using pipes for inter-process communication. It also features a hierarchical file system. Historically, the proprietary licensing led to many divergent and incompatible Unix versions, an era famously known as the "Unix wars".

This fragmentation led to a crucial push for standardisation. Key efforts include POSIX (Portable Operating System Interface), developed by IEEE as a compromise API for different Unix branches, and the Single UNIX Specification (SUS), now administered by The Open Group. Today, UNIX® (all caps) is a registered trademark owned by The Open Group. Only operating systems that pay for and pass stringent certifications can officially bear this trademark, signifying compliance with the SUS. This distinguishes certified UNIX systems from "Unix-like" ones.

While Linux is a "Unix-like" operating system, inspired by Unix and largely adhering to POSIX standards, it was written from scratch by Linus Torvalds and his community, and is not derived from the original Unix source code. In contrast, BSD systems (like FreeBSD or macOS, which is a certified UNIX operating system) are considered more directly "Unix" due to their genealogical link to the original AT&T Unix source code.

Although Linux has largely surpassed Unix in popularity across many modern computing domains, including web servers, supercomputers, and mobile devices, proprietary Unix variants such as IBM AIX, HP-UX, and Oracle Solaris continue to be widely used in high-end, mission-critical enterprise systems. These systems are valued for their robustness, stability, and ability to handle high workloads efficiently.