The Grassroots series has been designed to meet the students needs. The books address core subjects, are concise and affordable. They provide the student with enough resources and support, to pass a one semester course. Grassroots books have a common theme; they will inspire, educate and stimulate even the most reluctant of students. Macmillan Press, the Authors, and the series editor, Fintan Culwin are all working towards a standard of excellence which will enlighten and encourage the reader to extend their knowledge. Operating Systems has a traditional arrangement of material. Chapter 1 introduces the reader to operating systems, and gives an overview of the rest of the book. Chapter 2 covers the traditional material on processes, but with more emphasis than usual on threads. Chapter 3 considers interactions between concurrent threads, including semaphores, message queues, and monitors. On the assumption that this is the only place where a student will meet concurency, it goes into the topic in some detail. Memory management is covered in Chapter 4, including segmentation and paging. Input/Output is dealt with over two chapters: Chapter 5 concentrates on the high-level, device independent aspects, while Chapter 6 looks at low-level aspects such as the interface with hardware, control of devices, and file organisation on disk. Chapter 7 introduces the reader to distributed computer systems, and goes into some detail on communication mechanisms, and various distributed services which can be built on top of these. Finally, Chapter 8 looks briefly at fault handling and security issues, in both stand-alone and distributed systems.