Definition of Octal Number System: The octal number system is the base-8 number system, and uses the digits 0 to 7. That is to say 10octal represents eight and 100octal represents sixty-four.
In the early phase of modern computer development, 6-bit, 12-bit binary words were vastly used. Octal numbers were ideal for abbreviating those words. In the current times, however, 32-bit, 64-bits and even bigger binary words are used in computers.
Definition of Hexadecimal Number System: The hexadecimal (also base-16 or simply hex) number system is a positional numeral system that represents numbers using a base of 16. Unlike the decimal system representing numbers using 10 symbols, hexadecimal uses 16 distinct symbols, most often the symbols '0–9' to represent values 0 to 9, and 'A–F' (or alternatively 'a–f') to represent values from 10 to 15.