Books devoted to a description of internal structures and algorithms that form the basis of the operating system (so-called "core"), and explain their relationship to the program interface. Thus, it will be useful for those working in different operating environments. Firstly, it can be used as a textbook for the course "Operating Systems" for undergraduates and graduate students for the first year. When working with the book would have been much more useful to refer directly to the source code of system software, but the book can be read independently of him. Secondly, this book can serve as a guide for system programmers, of which the latter would be better able to understand the mechanism itself of the core operating system and to compare the algorithms used to UNIX, and the algorithms used in other operating systems. Finally, programmers working in the environment of UNIX, can deepen their understanding of the mechanism of interaction with the operating system software, and thereby come to write more efficient and sophisticated programs.