This chapter explains how to convert between the decimal, binary, octal and hexadecimal systems. Man's earliest number or counting system was probably developed to help determine how many possessions a person had. As daily activities became more complex, numbers became more important in trade, time, distance, and all other phases of human life. The advantages of digital computers include speed, accuracy and man-power savings. Often computers are able to take over routine jobs and release personnel for more important work that cannot be handled by a computer. Because binary notation requires so many bits to represent relatively small numbers, two further compact notations are often used, called octal and hexadecimal.