In the course of analysis of performance of computer programs constructed on the base of algorithms presented in this book, one should carefully take peculiarities of computer arithmetics into account. To this circle of problems belong questions concerning realizations (without overflows) of arithmetic operations and also other aspects of employing computers to perform numerical computations. In solve large problems, the question of running time becomes also very important. Without clear ideas about of how computers work, one cannot really examine these problems. In this chapter, we present some ideas which are necessary for understanding of peculiarities of realizations of algorithms in the framework of the concept of guaranteed accuracy.