Which number system does a computer use to store data and perform calculations?

A computer stores data and performs calculations using the binary number system of only two digits, 0 and 1.

These two digits map neatly onto the two states of an electronic switch, off and on.

The octal system uses eight digits and is only a shorthand grouping of binary, not what the hardware works in.

The decimal system of ten digits is how humans count, but circuits cannot hold ten stable states easily.

The hexadecimal system of sixteen digits is again a compact way for people to read binary, not the internal base.

Every letter, image and instruction is finally reduced to strings of these binary bits inside the machine.