Which number system uses two different digits?

The number system that uses two different digits is the Base 2 number system, commonly known as the binary system. In binary, the two digits utilized are 0 and 1. This is the foundational numbering system for computers and digital electronics, where all data is represented in terms of these two digits.

In contrast, the Base 10 number system, also known as the decimal system, employs ten different digits ranging from 0 to 9. The other options are based on different counts of digits: Base 5 uses five digits (0, 1, 2, 3, 4), and Base 8 uses eight digits (0 through 7). Thus, the only system among the choices that specifically involves just two different digits is the Base 2 number system.