Octal

Octal is rarely used in computing these days, although I think it's worth looking at so that you can see the similarities and consistencies between the different number bases.

If you are studying for GCSE Computer Science, then you should make sure that you understand binary and hexadecimal before looking at octal. You can also investigate other number bases using the number base abacus.

Octal is base 8, which means that the column headings increase by a factor of 8 as you move to the left, and there can be eight possible digits (0-7) in each position.

You can click the digits below investigate how to make a hexadecimal number. Clicking each digit with the left mouse button increases it by one, and when it gets to 8, it goes back to 0. Clicking the right mouse button (or a long-tap on a touch-screen) decreases the digit by one.

If you change the hexadecimal number so that it reads 0034, for example, that means that you want three 8s and four 1s, so the value of 0034 is 26. It's as simple as that!

Click the digits to investigate. Can you make 100? Is there only one pattern of digits that make each number? As you can see, octal numbers get bigger more quickly than binary numbers. What's the maximum value that you can store in a four-digit number like the one above?

Octal numbers can be converted directly to binary using a similar method to converting hexadecimal to binary, except that each octal digit becomes three bits rather than four..

For a more in-depth discussion of number bases, look at the Number Bases page in the Mathematics section.  You can also watch videos on number bases on the AdvancedICT YouTube channel.