base 8

Base 8 (or octal) is a number system with only the digits from 0 to 7. It is (or used to be) useful in computing/digital systems, because each digit is represented by exactly three bits, or three digits of base 2.

Binary | Octal | Decimal
------------------------
 0000  |   0   |   0
 0001  |   1   |   1
 0010  |   2   |   2
 0011  |   3   |   3
 0100  |   4   |   4
 0101  |   5   |   5
 0110  |   6   |   6
 0111  |   7   |   7
 1000  |  10   |   8
 1001  |  11   |   9
 1010  |  12   |  10
 1011  |  13   |  11
 1100  |  14   |  12
 1101  |  15   |  13
 1110  |  16   |  14
 1111  |  17   |  15

Thus, it is easy to convert numbers between binary and octal, simply convert three and three bits. Example: 1000110110₍₂₎ = 1 ; 000 ; 110 ; 110₍₂₎ = 1066₍₈₎

See also hexadecimal for a similar explanation of base 16.

---

"Base 8 is just like base 10, really. If you're missing two fingers!"
- Tom Lehrer