This book is designed with the goal of providing a comprehensive understanding of the structure of a computer and its operations, the RTL and Micro-level operations and control in a computer, the concepts of I/O and memory organization and operating systems. Able to visualize the organization of different blocks in a computer, able to use micro-level operations to control different units in a computer, able to use Operating systems in a computer in a single textbook. In addition, the book contains an entire chapter on computer organization and operating systems. This book covers both the fundamentals of computer organization and operating systems. Separate chapters are allocated to cover design methodologies of simple and complex combinational and sequential circuits. The book covers Basic Structure of Computers, Register Transfer Language and Micro Operations, Micro Programmed Control, The Memory System, Input-Output Organization, Operating Systems Overview, memory organization, Principles of Deadlock, File System Interface and File System Implementation.