Computer Architectures

Assembler programming is a very low-level technique for writing the software. It uses the hardware directly relying on the architecture of the processor and computer with the possibility of having influence on every single element and every single bit in hundreds of registers which control the behaviour of the computer and all its units. That gives the programming engineer much more control over the hardware but also requires a high level of carefulness while writing programs. Modification of a single bit can completely change the way of a computer’s behaviour. This is why we begin our book on the assembler with a chapter about the architecture of computers. It is essential to understand how the computer is designed, how it operates, executes the programs, and performs calculations. It is worth mentioning that this is important not only for programming in assembler. The knowledge of computer and processor architecture is useful for everyone who writes the software in any language. Having this knowledge programming engineers can write more efficient applications in terms of memory use, time of execution and energy consumption.

You can notice that in this book we often use the term processor for elements sometimes called in some other way. Historically the processor or microprocessor is the element that represents the central processing unit (CPU) only and requires also memory and peripherals to form the fully functional computer. If the integrated circuit contains all mentioned elements it is called a one-chip computer or microcontroller. A more advanced microcontroller for use in embedded systems is called an embedded processor. An embedded processor which contains other modules, for example, a wireless networking radio module is called a System on Chip (SoC). From the perspective of an assembler programmer differentiating between these elements is not so important, and in current literature, all such elements are often called the processor. That's why we decided to use the common name “processor” although other names can also appear in the text.