Until the early 1970’s, computers tended to occupy entire rooms. Generally, they were liquid cooled using water. Then computers were mostly used to carry out business transaction processing (eg. banks). Both the scientific and engineering communities wanted to be able to use the computing power in their fields. The issue that they had to work around was the fact that the operating systems that existed then were designed to support transaction processing.
Bell labratories began working on developing their own operating system to better serve the needs of their research and engineering groups. They created a language called B (I’ve heard that it stands for Bell) which was designed to allow them to write/program the operating system. However, that still didn’t give them a language which would allow them to write their own applications. So, that lead them to develop the C language (named by virtue of being the letter after B) which would serve both the purpose of low level operating system development and high level application development language.
This eventually lead to the first implementation of unix running on a Digital Equipment (DEC) PDP 11/44 (I used one of those in college). Most operating systems consist of 2 parts. The first is called the kernel (reference to a seed). What it consists of is the boot program, a set of process control programs, and configuration file(s) which tell it what programs to load during boot. The second part of the operating system is everything else that is installed with the OS including the user interface. In unix the kernel is written in the assember language for the processor that it is running on. But almost all of the remainder of unix is written in C (or C++).
The major advantage to this was that it made unix very easy to migrate to a different platform, since only the kernel (and the C Compiler) had to be rewritten for the new hardware. And that was what happened. Within a short time, there were hundreds of versions of unix because each group that worked with it added their own feature to their implementation. Eventually, this lead to the standardization of 2 variants of unix. Bell’s version was called System V (still in use by Sun Microsystems, Santa Cruz Operation) and BSD (Berkeley). Linux is an implementation of BSD unix.
What is interesting about unix (including linux) is that the source code for the operating system is and always has been publicly available. Linux came about when Intel Pentium processors had the performance to fully support both server and GUI processing requirements. The first version of unix for a PC that I was aware of was SCO. At that time it was a text based implementation.
As far as I know, the widespread interest in porting unix to PCs never dropped off. What I believe the reason for that is, is that unix was designed by engineers and scientists to meet their need for maximizing the calculating power of the hardware. And so, it has been optimized for things like 2D & 3D calculating and rendering. In all of the credits of the pixar films, I’ve seen is a credit to Sun Microsystems. Pixar uses Sun Workstations (running unix) and servers to render the animations.