Data Representation

Introduction

In this unit you learn why computers represent EVERYTHING using binary. This includes numbers, text, sound, images and videos. We look at how to convert numbers between binary, denary and hexadecimal; and look at examples of the use of hexadecimal in real applications. We look at how data is compressed using lossless and lossy compression techniques.

Subpages

1. Representing Numbers and Applications of Hexadecimal
2. Representing Text & Lossless Compression
   • Text files are usually .txt file extension. (.docx, .doc, .odt, .pdf, etc... contain more than just plain text!)
   • General lossless compression are files like .zip, .gz.
3. Representing Images, Sound and Video & Compression
   • Images: Vector (.svg, .ps, .ai), Bitmapped (.bmp, .gif, .png, .jpg)
   • Sound: Midi (.mid), Sampled (.wav, .mp3, .flac, .ogg, .wma, .aiff, .aac, etc...)
   • Video: (.mpg, .avi, .wmv,. etc...)
4. Exam-style Questions - See Assessment revision papers

External Resources

• BBC Bitesize: Binary and Data Representation
• GCSE CS Guru: Data Representation, Data Storage
• Understanding ASCII (YouTube Video)
• AP Computer Science Principles on Code.org: Unit 2 Digital Information
• AP Computer Science Principles on Khan Academy: Digital Data, Computer Files, Compression
• Quizlet - Data Representation Flash Cards
• Quizziz - GCSE Data Representation Quiz

Dot points

Binary and Hexadecimal

• recognise the use of binary numbers in computer systems
• convert positive denary integers into binary and positive binary integers into denary (up to 16 bits)
• show understanding of the concept of a byte and how the byte is used to measure memory size
• use binary in computer registers for a given application (such as in robotics, digital instruments and counting systems)
• represent positive numbers in hexadecimal notation
• show understanding of the reasons for choosing hexadecimal notation to represent numbers
• convert positive hexadecimal integers to and from denary (a maximum of four hexadecimal digits will be required)
• convert positive hexadecimal integers to and from binary (a maximum of 16 bit binary numbers will be required)
• represent numbers stored in registers and main memory as hexadecimal
• identify current uses of hexadecimal numbers in computing, such as defining colours in Hypertext Markup Language (HTML), Media Access Control (MAC) addresses, assembly languages and machine code, debugging (revisit in context later)

Data Storage

• show understanding that sound (music), pictures, video, text and numbers are stored in different formats
• show understanding of the concept of Musical Instrument Digital Interface (MIDI) files, JPEG files, MP3 and MP4 files
• show understanding of the principles of data compression (lossless and lossy) applied to music/video, photos and text files
• calculate the storage requirement of a text, image, sound or video file
• Optional (also in Data Transmission Unit): identify and describe methods of error detection and correction, such as parity checks, check digits, checksums and Automatic Repeat reQuests (ARQ)