# The most frequently asked question by students who are studying automation is: Why do we have to learn number systems?

Well...let's think of it this way. If you were visiting a forign country you would want to learn a-bit of the language that is spoken in that country. Phrases like, where is the rest room? Can you direct me to the train station? Think of PLC/PAC's as a forign country and the language spoken is numbers.

PLC/PAC's use four number systems:
(Click the number system for more information and converting to other number systems.)

Decimal
The decimal number system is the number system we use everyday. 'Deci' means 10, therefore there are 10 valid numbers, 0 through 9. Decimal is a 'base 10' number system.
Binary
The binary number system is the number system used by computers, PLC/PAC's and any other equipment and devices that are digital. 'Bi' means 2, therefore there are 2 valid numbers, 0 and 1. Binary is a 'base 2' number system.
Octal
The octal number system is a number system used by early PLC/PAC's. 'Octa' means 8, therefore there 8 valid numbers, 0 through 7. There are no 8's or 9's in this number system. Octal is a 'base 8' number system.