The textbook covers the section "Arithmetic basics of computers" of the discipline "Discrete mathematics." The manual describes the features of representation of fixed and floating point numbers in different formats adopted in personal computers, general-purpose computers and microcomputers. Methods for performing arithmetic operations (addition, multiplication and division) on fixed and floating point numbers, on decimal numbers are described. To consolidate the theoretical material, you need to complete the homework proposed in the manual. Each task contains its own wording, the basic provisions, the knowledge of which is necessary for the student to perform it, as well as a large number of examples explaining the methods of representing numbers in a computer and the principles of performing operations on them. Examples are provided with the necessary comments.