Why do digital computer use binary number system?

Answer 1

Binary numbers have only 2 digits, 0 and 1. Binary came from a need to represent information based in magnetics that only offer an "on" or "off" state. Decimal numbers have 10 digits, 0,1,2,3,4,5,6,7,8,9. Decimal numbers came about from humans having 10 fingers to count with. Once they reach 10, they start reusing fingers (digits).

When humans count to 3, they count to their 3rd digit.

Here's how to count to 3 in binary, which only has 2 digits: 01,10,11

Here's counting to 7 in decimal: 1,2,3,4,5,6,7

Here's counting to 7 in binary: 001,010,011,100,101,110,111

All of the mathematics done in decimal can be done in binary.

No matter how fancy computers get, the bottom line is they have to store and manipulate information at a physical level, something physical must store all of that information. In computers, that physical storage is magnetic. All information is stored and manipulated at the lowest level as a combination of large binary values, large combinations of "on" and "off".

Scientists are inventing new ways to store information in computers, so perhaps in time computer storage won't be limited to binary values.