... level language rather than assembly language Allow re-use of code Typical vendor operating systems of the time were extremely large and all written in assembly language. UNIX had a relatively small amount of code written in assembly language (this is called the kernel) and the remaining code for the operating system was written in a high level language called C. The group worked primarily in the high level language in developing the operating system. As this development continued, small changes were necessary in the kernel and the language to allow the operating system to be completed. Through this evolution the kernel and associated software were extended until a complete operating system was written on top of the kernel in the language C. UNIX APPLICATION PROGRAMMING INTERFACE Many proprietary operating systems have a simplified view of application behavior. The typical application reads some data from disk, tape or a terminal and ...

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