# That Blue Square Thing

## AQA Computer Science GCSE

July 2019: the AQA CompSci area is almost complete. Most of the content for units 3-6 is now up and there's quite a lot of Unit 7 material. There's still some work to do, particularly on Paper 1 units, but it's getting there.

### Data Representation - Binary Numbers

Computers are, at their heart, very complex machines which use a very simple way of storing information. It all comes down to Binary numbers - 1s and 0s.

Binary Numbers - binary and denary - an introduction

#### Converting Binary to Decimal and Back Again

You need to be able to convert from binary to denary.

And you need to be able to convert from denary to binary as well. Which is a little harder.

#### Why Binary?

Absolutely everything that a computer does can only be stored using binary numbers. Every single thing has to be able to be reduced down to a series of 1s and 0s to get it inside a computer of any kind.

Just think of what that means:

• every instruction that a program executes has to be stored as binary numbers. So when you type Python code it gets translated into a set of 1s and 0s so that it can be executed
• a photograph, which shows thousands of different shades of colours, ends up as 1s and 0s. Every digital photo of a work of complete artistic genius ends up as 1s and 0s
• every piece of writing has to be stored as 1s and 0s. Whether it's a quick e-mail, the complete works of William Shakespeare or today's newspaper. It all becomes 1s and 0s once you get it typed and stored electronically
• music, if it's stored digitally, ends up as 1s and 0s. The most complex, richest, dynamic music you can imagine. If it's in a computer it's just 1s and 0s

The reason for all this is that computers just can't deal with anything else. A switch can only be on or off - it can be a 1 or a 0. Nothing else.

Why Binary? - some theory which reminds you why we need to use binary.

More Complex Why Binary? - this details some of the ways in which data storage has developed over time and some other ways in which data can be stored and transferred using alternatives to switches.

#### Number Bases - a Summary

The slides summarise how the three numbers bases (binary, decimal and hexadcimal) work. This is probably best left until you know about all of them and might be helpful for revision.

#### Binary Revision Questions

Revision questions, dealing with all of the binary stuff, will appear here:

Binary Revision Questions 1 - everything binary only

Binary Revision Questions 2 - binary and hex