This textbook offers an overview of computer architectures. In the first few chapters I cover topics relating to general computer hardware architecture and also the role of the operating system. Here I also deal with areas such as process management and memory management. Chapter 5 deals with issues relating to CPU design. General features of an 8-bit CPU are considered and a typical instruction set is designed. There follows an example of a CPU simulator written in C programming language. This is done to illustrate how the instructions are processed inside the Control Unit. Chapters 6 and 7 introduce the more advanced architecture topics such as pipelining and scaling. In particular Chapter 7 deals with parallel processing including the programming aspects for parallel execution.