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💻 1. Representation of Text

🔑 Key Idea​

  • Computers cannot understand letters directly
  • Text must be converted into binary (0s and 1s)

👉 Each character (letter, number, symbol) is stored as a binary code

🔤 Character Sets​

Definition​

A character set is a system that assigns a unique binary code to each character.

ASCII (American Standard Code for Information Interchange)​

Features​

  • Uses 7 bits (standard) → 128 characters
  • Extended ASCII uses 8 bits → 256 characters
  • Includes:
    • Letters (A–Z, a–z)
    • Numbers (0–9)
    • Basic symbols

Example​

CharacterASCII (Decimal)Binary
A6501000001
a9701100001

Unicode​

Features​

  • Uses more bits (typically 16 bits or more)
  • Can represent millions of characters
  • Includes:
    • All languages (e.g. Chinese, Arabic)
    • Symbols
    • Emojis 😊

ASCII vs Unicode​

FeatureASCIIUnicode
Bits used7 or 816+
CharactersLimitedVery large set
LanguagesMostly EnglishGlobal

Why Unicode is Needed​

  • ASCII is too limited for global communication
  • Unicode allows:
    • Multilingual text
    • Special symbols
    • Emojis

📌 Exam Tip:
Always say:

  • “Unicode allows a much wider range of characters”
  • “Uses more bits per character than ASCII”

🔊 2. Representation of Sound

🔑 Key Idea​

  • Sound is an analogue wave
  • Computers store sound as digital data

👉 Conversion process = Sampling

🎵 Sampling​

Definition​

Taking measurements of a sound wave at regular intervals and converting them into binary.

Sample Rate​

Definition​

  • Number of samples taken per second
  • Measured in Hertz (Hz)

Example​

  • 44,100 Hz (CD quality)

Effect​

  • Higher sample rate → more accurate sound
  • Higher file size

Sample Resolution (Bit Depth)​

Definition​

  • Number of bits used per sample

Example​

  • 8-bit, 16-bit, 24-bit

Effect​

  • Higher resolution → more precise amplitude values
  • Better sound quality
  • Larger file size

Summary of Effects​

FactorIncrease → Effect
Sample RateBetter quality, larger file
Sample ResolutionBetter quality, larger file

Example Explanation (Exam Style)​

A higher sample rate means more data points are captured per second, resulting in a more accurate representation of the original sound wave.

📌 Exam Tips

  • Use terms like:
    • “analogue to digital conversion”
    • “samples per second”
    • “accuracy of waveform”
  • Always link quality AND file size

🖼️ 3. Representation of Images

🔑 Key Idea​

  • Images are made of pixels (picture elements)
  • Each pixel is stored as binary data

Resolution​

Definition​

  • Number of pixels in an image

Example​

  • 1920 × 1080 = Full HD

Effect​

  • Higher resolution → more detail
  • Larger file size

Colour Depth​

Definition​

  • Number of bits used per pixel

Determines:​

  • Number of possible colours

Examples​

Bits per pixelColours
1 bit2 colours
8 bits256 colours
24 bits16.7 million colours

Effects of Colour Depth​

  • Higher colour depth →
    • More realistic images
    • Smoother colour transitions
    • Larger file size

Summary of Effects​

FactorIncrease → Effect
ResolutionMore detail, larger file
Colour DepthMore colours, larger file

Example Explanation (Exam Style)​

Increasing the resolution increases the number of pixels, which improves image detail but also increases the file size.

📌 Exam Tips

  • Always mention:
    • “pixels”
    • “binary representation”
  • Link quality + file size

🧠 Key Definitions

  • Pixel: Smallest unit of an image
  • Resolution: Number of pixels
  • Colour Depth: Bits per pixel
  • Sample Rate: Samples per second
  • Sample Resolution: Bits per sample
  • Character Set: Mapping of characters to binary

⚠️ Common Exam Mistakes

❌ Confusing:

  • Sample rate vs sample resolution
  • Resolution vs colour depth

❌ Forgetting:

  • To mention file size increases
  • That sound is analogue originally
  • That text uses character sets

📝 High-Value Exam Answers

Why does increasing sample rate improve sound quality?​

  • More samples per second
  • More accurate waveform representation

Why does higher resolution improve images?​

  • More pixels → more detail

Why is Unicode better than ASCII?​

  • Supports more characters
  • Includes multiple languages and symbols

🔥 Final Quick Summary

  • Text → Character sets (ASCII, Unicode)
  • Sound → Sampling (rate + resolution)
  • Images → Pixels (resolution + colour depth)
  • Increasing quality → always increases file size