This modularity
made it possible for lots of code to be developed by lots of different people.
Portability??”Much of the early work in simplifying the experience of using UNIX led
to its also becoming extraordinarily portable to run on different computers. By having
device drivers (represented by files in the file system tree), UNIX could present an interface
to applications in such a way that the programs didn??™t have to know about the details
of the underlying hardware. To later port UNIX to another system, developers had only to
change the drivers. The applications didn??™t have to change for different hardware!
To make the concept of portability a reality, however, a high-level programming language
was needed to implement the software. To that end, Brian Kernighan and Dennis Ritchie
created the C programming language. In 1973, UNIX was rewritten in C. Today, C is
still the primary language used to create the UNIX (and Linux) operating system
kernels.
As Ritchie went on to say in his 1980 lecture:
Today, the only important UNIX program still written in assembler is the assembler itself;
virtually all the utility programs are in C, and so are most of the applications programs,
although there are sites with many in Fortran, Pascal, and Algol 68 as well.
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