The author presents the basics and concepts of today's operating systems and covers the areas of processes (process states, process scheduling, process synchronization, and process communication), memory management (virtual memory, paging, swapping), file management (files, folders, security mechanisms), input and output management (drivers, I/O memory mapping, system functions), as well as networks (network layers, work distribution, shadow servers) and security mechanisms (types of attacks, root kits, Kerberos). Single-processor as well as multi-processor systems are considered, and the concepts of important existing operating systems such as Unix and Windows NT are clarified. In this fourth edition, many experiences from teaching practice have been taken into account. Thus, not only the developments in Windows NT and Unix, especially Linux, were updated, but also.