Hexadecimal (also base 16, or hex) is the base-16 positional numeral system, using the 16 symbols 0–9 and A‒F.
The octal numeral system, or oct for short, is the base-8 numeral system, using the digits 0 to 7
"The octal encoding mechanism is less error-prone than hex so i ll demonstrate using octal"
from question "Telnet Session using Expect Module fails to send command ctrl+A"
"Apparently octal format was more popular than hex format"
from question "Why fcntl() flag values are defined in Octal format & how this function works for blocking/non-blocking sockets?"
"From what i understand octal was more popular than hex among users of 18-bit architectures since a word would be exactly 6 octal digits"
from question "Can you encode values expressed as binary digits directly in the c-family of languages?"