Cambridge IGCSE Computer Science - Data Representation and Transmission Notes

Cambridge Assessment International Education

  • Endorsed for syllabus coverage in Cambridge IGCSETM and O Level Computer Science.

Hodder Education Resources

  • Offers Student’s Book, Boost eBook, Workbooks, and Teacher’s Guide.

  • Includes digital learning resources and online solutions.

Copyright Information

  • Material reproduced under license from Cambridge Assessment International Education.

  • Third-party websites not endorsed.

Publication Details

  • Published by Hodder Education in 2021.

Contents

  • Covers Computer Systems (Chapters 1–6) and Algorithms, Programming and Logic (Chapters 7–10).

Introduction

  • Aimed at Cambridge IGCSETM and O Level Computer Science students for examination from 2023.

  • Develops skills in programming, problem-solving, and introduces new technologies.

Assessment

  • Two examination papers: Computer Systems and Algorithms, Programming and Logic.

How to Use This Book

  • Organized into 10 chapters.

  • Includes learning outlines, introductions, activities, examples, advice, links, extensions, summaries, key terms, and exam-style questions.

  • Uses pseudocode, Python, VB.NET, and Java with IDE instructions in the Programming, Algorithms and Logic Workbook.

  • Additional support provided by Computer Systems Workbook and Programming, Algorithms and Logic Workbook.

  • Command words and their meanings (Table provided for reference).

Section 1 Computer systems

  • Chapters cover data representation, data transmission, hardware, software, internet uses, and automated technologies.

1 Data representation

  • Covers number systems, text/sound/image representation, and data storage/compression.

1.1 Number systems
1.1.1 Binary represents data

  • Computers use binary (1s and 0s) via tiny switches and logic gates.

1.1.2 Binary, denary and hexadecimal systems

  • Denary: Base 10, digits 0-9.

  • Binary: Base 2, digits 0 and 1.

  • Hexadecimal: Base 16, digits 0-9 and A-F.

  • Conversion methods between these systems provided.

1.1.3 Use of the hexadecimal system

  • Hexadecimal is convenient for representing binary data (1 hex digit = 4 binary digits).

  • Used in error codes, MAC addresses, IP addresses, HTML color codes.

1.1.4 Addition of binary numbers

  • Binary addition rules: 0 + 0 = 0, 0 + 1 = 1, 1 + 0 = 1, 1 + 1 = 10

1.1.5 Logical binary shifts

  • Logical shift: Moving binary numbers left (multiplies by 2) or right (divides by 2).

1.1.6 Two’s complement (binary numbers)

  • Represents negative integers; left-most bit indicates the sign.

1.2 Text, sound and images
1.2.1 Character sets – ASCII code and Unicode

  • ASCII: 7-bit or 8-bit codes for letters, numbers, characters.

  • Unicode: Represents all languages, supports up to four bytes per character.

1.2.2 Representation of sound

  • Sound waves sampled using ADC; sampling rate and resolution affect quality and file size.

1.2.3 Representation of (bitmap) images

  • Bitmap images: Pixels in a 2D matrix.

  • Colour depth: Bits used per color.

  • Resolution: Number of pixels.

1.3 Data storage and file compression
1.3.1 Measurement of data storage

  • Units: Bit, Byte, Nibble, KiB, MiB, GiB, TiB, PiB, EiB.

1.3.2 Calculation of file size

  • Image File Size: resolution × color depth.

  • Sound File Size: sample rate × sample resolution × length (×2 for stereo).

1.3.3 Data compression

  • Reduces storage space and transfer times.

1.3.4 Lossy and lossless file compression

  • Lossy: Eliminates data, irreversible; examples: MP3, MP4, JPEG.

  • Lossless: Reconstructs original data; used RLE.

2 Data transmission

  • Covers data packets, transmission methods, error detection, and encryption.

2.1 Types and methods of data transmission
2.1.1 Data packets

  • Data split into packets with headers, payloads, and trailers for independent routing and error checking.

2.1.2 Data transmission

  • Modes: Simplex, half-duplex, full-duplex.

  • Methods: Serial (one bit at a time), parallel (multiple bits at once).

2.1.3 Universal serial bus (USB)

  • Standardized serial data transmission for device-computer communication.

2.2 Methods of error detection
2.2.1 The need to check for errors

  • Errors occur due to interference or skewing of data and are found with parity checks, checksums, and echo checks.

2.2.2 Parity checks, checksum and echo checks

  • Parity checks: