Comment by jonjacky

It is often said that C became popular just because Unix was popular, due to being free -- it just "rode its coattails" as you put it.

As if you could separate Unix from C. Without C there wouldn't have been any Unix to become popular, there wouldn't have been any coattails to ride.

C gave Unix some advantages that other operating systems of the 1970s and 80s didn't have:

Unix was ported to many different computers spanning a large range of cost and size, from microcomputers to mainframes.

In Unix both the operating system and the applications were written in the same language.

The original Unix and C developers wrote persuasive books that taught the C language and demonstrated how to do systems programming and application programming in C on Unix.

Unix wasn't the first operating system to be written in a high-level language. The Burroughs OS was written in Algol, Multics was written in PL/I, and much of VMS was written in BLISS. None of those languages became popular.

IN the 1970s and 80s, Unix wasn't universal in universities. Other operating systems were also widely used: Tenex, TOPS-10, and TOPS-20 on DEC-10s and 20s, VMS on VAXes. But their systems languages and programming cultures did not catch on in the same way as C and Unix.

The original Macintosh OS of the 1980s was no competitor to Unix. It was a single user system without integrated network support. Apple replaced the original Macintosh OS with a system based on a Unix.