Octal and hexadecimal notation. Because binary notation can be cumbersome, two more compact notations are often used, octal and hexadecimal. Octal notation represents data as base-8 numbers. Each digit in an octal number represents three bits.Similarly, hexadecimal notation uses base-16 numbers, representing four bits with each digit.Octal numbers use only the digits 0-7, while hexadecimal numbers use all ten base-10 digits (0-9) and the letters a-f (representing the numbers 10-15).imilarly, hexadecimal notation uses base-16 numbers, representing four bits with each digit. Octal numbers use only the digits 0-7, while hexadecimal numbers use all ten base-10 digits (0-9) and the letters a-f (representing the numbers 10-15).