# That Blue Square Thing

## Computer Science GCSE

Note: this page deals with the old Edexcel GCSE (grades A-G) which no longer exists. I'm keeping it as an archive and because a number of the resources will still apply to newer (grades 1-9) courses. The AQA GCSE CompSci pages deal with a current course.

Hexadecimal numbers use base 16 - so you can use one digit to county up to 15. The letters A to F are added on after 9, so A = 10, B = 11 and so on until F = 15. That gives you 16 possible values - including the 0.

Hexadecimal isn't used by computers, but it is an easy thing for humans to use when we're trying to talk in binary. And it converts really easily.

You need to be able convert hexadecimal t0 8-bit binary numbers and vice-versa. This is actually really easy to do and shouldn't cause any problems - so long as you remember that A = 10!

Hexadecimal basics - notes on how it all works

Just remember that A = 10 and F = 15. It's really easy to get into thinking that A is 11 and F is 16. It's not! Get this right and hexadecimal is a piece of cake.

#### Revision exercises

There's likely to be one mark on hexadecimal on the exam. So make sure you get it!

The BBC Bitesize website has a section on hexadecimal that you might want to look at. Well worth a look.