Base-4 (aka quaternary) number system uses four symbols to code information. Most commonly, these symbols are, 0, 1, 2 and 3.
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.