Thread Academy

Text and Characters

See how ASCII and Unicode turn letters into numbers.

  • Define and explain Text and Characters in your own words
  • Use key terms such as denary accurately
  • Apply what you have learned to new examples and questions
  • Avoid the common mistakes learners make with this topic

This lesson focuses on Text and Characters: see how ASCII and Unicode turn letters into numbers.

Definition: Text and Characters

See how ASCII and Unicode turn letters into numbers.

Key ideas

Everything is binary underneath

Text, images, sound and video are all stored as patterns of bits — the computer just interprets the patterns differently. The binary pattern 01000001 means the letter 'A' in text, but the same pattern could mean the number 65 or a dark pixel in an image. Meaning comes from context, not from the bits themselves.

More bits means more detail

With n bits you can represent 2 to the power of n different values: 8 bits give 256 colours or characters, while 24 bits give over 16 million colours. Higher colour depth, higher image resolution and higher sound quality all cost more bits — a trade-off between quality and file size.

Key term — denary: The ordinary base-10 number system we use every day, with the digits 0 to 9. Also called decimal.

Worked example: Text and Characters

A sound file sampled at a higher rate is larger. Why?

A higher rate takes more samples every second, so more numbers must be stored — better quality costs more bits.

Answer: A higher rate takes more samples every second, so more numbers must be stored — better quality costs more bits.

Common mistakes
  • Thinking 8 bits can store the number 999 Correction: 8 bits hold 0 to 255 only; larger numbers need more bits — check 2 to the power of n first.
  • Reading binary left to right as if the leftmost digit is worth 1 Correction: the rightmost column is always worth 1 — write the place values above the digits before adding.

Practice

The letter 'A' is stored as 01000001. What number is that in denary, and why might the same pattern mean something else elsewhere?
Convert, then think about context.

65 — and the same bits could be a colour value or part of an image, because meaning comes from how the program interprets the bits.

Convert the binary number 1101 to denary.
Place values are 8, 4, 2, 1 — add the ones with a 1.

13 — that is 8 + 4 + 1.

Write denary 20 as a binary number.
The biggest place value that fits is 16.

10100 — that is 16 + 4.

True or false: adding one more bit to a code doubles the number of values it can represent.
Compare 2 to the power of n with 2 to the power of (n + 1).

True — each extra bit doubles the combinations, since every existing pattern can end in either 0 or 1.

Quick check

Text and Characters — quick check

Which of these best defines "denary"?

The ordinary base-10 number system we use every day, with the digits 0 to 9. Also called decimal.

How many different values can 4 bits represent?

16 — from 0 to 15.
Key takeaways
  • Text and Characters: see how ASCII and Unicode turn letters into numbers.
  • Everything is binary underneath: Text, images, sound and video are all stored as patterns of bits — the computer just interprets the patterns differently.
  • bit: A single binary digit — a 0 or a 1.
  • Watch out for: thinking 8 bits can store the number 999
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