This book was written to meet the needs of the curricula of Greek Universities with a text that would introduce the student to the structure and functioning of a Computer System.

An effort is made to present concepts such as microprocessor, memory, memory decoding, addressing methods, input-output units, interrupts, etc., which, when understood and owned by the reader, will help them grasp the structure and logic of a computer system.

Reference is made to the MOTOROLA MC68000 microprocessor as a classic representative of CISC technology, to the ATMEL AVR ATmega8515 microcontroller as a classic representative of RISC technology, and to the Arduino application development system, which is the most user-friendly open hardware and software microcontroller system for embedded systems applications.