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IGCSE · Practice questions · Representing text: ASCII and Unicode

Every key is a code.

Six original Cambridge-style questions on representing text with ASCII and Unicode, with worked solutions.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

One code per character.

01
Explain
[2 marks]

Explain why a computer needs a character set to represent text.

  • Text must be converted to binary to be processed by a computer. ✓
  • A character set gives each character a unique binary code, so all computers using it read the codes as the same characters. ✓
02
Convert
[2 marks]

The ASCII code for D is 68. Give the 8-bit binary codes for D and F.

  • D: 68 = 01000100. ✓
  • F: 68 + 2 = 70 = 01000110. ✓
03
Explain
[3 marks]

Compare the ASCII and Unicode character sets.

  • ASCII uses fewer bits per character (7, or 8 for extended ASCII); Unicode uses more bits per character. ✓
  • ASCII represents a small range of characters (128 or 256), mainly English; Unicode represents a much greater range, including other languages and emojis. ✓
  • So the same text takes more storage in Unicode than in ASCII. ✓
04
Calculate
[2 marks]

A text file contains 2048 characters. Calculate its size in KiB if it is stored (a) in 8-bit ASCII and (b) in a 32-bit Unicode encoding.

  • (a) 2048 × 8 bits = 2048 bytes; 2048 ÷ 1024 = 2 KiB. ✓
  • (b) 2048 × 32 bits = 8192 bytes; 8192 ÷ 1024 = 8 KiB. ✓
05
Apply
[2 marks]

A company is building a chat app for users in China, India and Greece who like to send emojis. State which character set it should use and justify your choice.

  • Unicode. ✓
  • ASCII cannot represent Chinese, Hindi or Greek characters or emojis; Unicode has codes for all of them. ✓
06
Analysis
[2 marks]

A student says "Unicode should always be used because it is newer than ASCII." Give one reason why ASCII may still be chosen for a file containing only English text.

  • ASCII needs fewer bits per character. ✓
  • So the file would be smaller, using less storage and taking less time to transmit, and ASCII already covers all English characters. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.