The first positional number system in human history was invented by the Babylonians. They used a base 60 system. Remnants of this system can be found in the way that we measure time (60 seconds in a minute, 60 minutes in an hour).

Nowadays, we use a base 10 system, the decimal system. With the exception of the Babylonian and Mayan systems (the Mayans used a base of 20), all positional notations in human history were base 10. Probably the reason for this is because humans have 10 fingers. However, base 10 is not the only base that we could use. We could use base 8, or base 12, or base 16, or...

Of course, when using different bases, you need to convert from one base to another.