"Operating Systems Principles and Unix," serves as an exhaustive resource delving into the core aspects of operating system theory and practice. This text enables readers to gain a solid foundation in the architecture, execution, and administration of operating systems, encompassing key areas such as process control, memory management, file systems, and security protocols. Additionally, it offers a detailed look at the Unix operating system and its derivatives, unpacking its essential elements including commands, utilities, and functionalities, stretching from file manipulation to shell scripting and system maintenance. This guide adopts both theoretical and applied perspectives towards operating system principles, emphasizing UNIX with clarity. Comprising eight informative chapters, it aligns with the curricula for MCA, MSc., B.E., and BCA programs offered by numerous universities throughout India. This study material is specifically crafted to aid students in their preparations for competitive assessments like the NET, SLET, and other exams.