0200. Why do we use octal and hexidecimal?

The main reason is that it is very easy to convert from binary to either Octal (base 8) and hexidecimal (base 16). Given three (3) bits we can represent 8 items (2³ = 8) or all of the digits in the octal system (1 .. 7). Given four (4) bits we can represent 16 items (2⁴ = 16) or all of the digits in the octal system (1 .. A, B, C, D, E, F).