The octal system and the hexadecimal system have the advantage over the dual system that their number combinations can be easily converted to the dual system, but they do not have as long number sequences as pure dual numbers.
The octal system has a base of 8 and a character set of 0...7. The character set can be represented with three bits: from 000 for 0 to 111 for 7. This representation method was used in data processing in the past and is obsolete now. It was replaced by the hexadecimal system, which allows sixteen combinations, is represented in four bits and, in combination of two each, fills one byte and is therefore more convenient to handle than an octal representation.