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J277 1.2.4 Characters and text

Part 1 of 5 · J277 1.2.4-1.2.5 · Data representation

How text is stored in binary, covering character sets, ASCII, Unicode and text-file size.

Students will:

  • explain what a character set is
  • explain how characters are represented in binary
  • relate bits per character to the number of available codes
  • compare ASCII and Unicode
  • calculate the size of a simple text file

Inside: 6 text sections, 2 multiple-choice activities, 5 completion activities, 3 written answers. 16 marks. Suggested teaching time: 40–55 minutes. 1 diagram.

Includes a teacher guide with suggested sections, timings and common misconceptions.

Series: J277 1.2.4-1.2.5 · Data representation, part 1 of 5.

Shared by Coding PathwayVerified teacher

  • 16 cells
  • About 45 minutes
  • CC BY-SA 4.0
  • Shared 17 Aug 2026
  • Updated 27 Oct 2026

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The whole resource, exactly as a class sees it. Answers and marking are held back.

Characters and text

Computers store text using binary codes. A character can be a letter, digit, punctuation mark, space or another symbol. You will use a code table, compare character sets and calculate a small text file's size.

Multiple choice1 mark

Why can computer circuits represent text using binary codes?

  • AThey can represent two states using 0 and 1
  • BA binary digit is a printed letter
  • CText always becomes smaller in binary
  • DEvery character must be represented by 1

1. A code for each character

A character set is the collection of characters a computer can represent. Its code table matches each character to a unique binary code. Software uses this mapping to interpret the stored code.

If different characters shared a code in the same set, software could not tell which one was intended.

Characters and their eight-bit codes Three rows associate A with 01000001, B with 01000010 and C with 01000011. Each character has a different code; adjacent uppercase letters have consecutive values in this example. One character, one code A B C 01000001 01000010 01000011 These are supplied codes, not a memory test.
Fill in the blanks3 marks
A Answer 1 matches characters to their Answer 2. Different characters need Answer 3 codes.
  • character set
  • binary codes
  • unique
  • identical

2. More possible codes

Each extra bit doubles the number of possible patterns. For example, 2 bits allow 4 patterns, 3 bits allow 8 and 4 bits allow 16. The rule is 2 to the power of the number of bits.

This is the number of different characters available, not the number of characters in a particular file.

Fill in the blanks1 mark
A code uses 5 bits for each character. It can provide up to Answer 1 different codes.

3. ASCII and Unicode

ASCII provides a limited range of characters, including English letters, digits and punctuation. Unicode supports a much wider range of writing systems and symbols.

Using more bits per character allows more possible codes, but can increase the file size for the same number of characters. Unicode encodings do not all use one fixed number of bits: use the value stated in a question.

OCR questions show ASCII codes using 8 bits. The supplied A, B and C codes are consecutive: the next uppercase letter has a code one greater. Uppercase and lowercase letters have different codes; do not assume that every pair of symbols is consecutive.

Multiple choice1 mark

Which statement correctly compares Unicode with a limited ASCII character set?

  • AUnicode has fewer possible characters
  • BUnicode can represent more writing systems and symbols
  • CUnicode always uses exactly 16 bits per character
  • DUnicode makes every text file smaller
Fill in the blanks1 mark
The supplied table gives C = 01000011. The code for the next uppercase letter, D, is Answer 1.
Fill in the blanks2 marks
Use the supplied table to encode BA, without adding the codes. (a) B: Answer 1 (b) A: Answer 2

4. Text-file size

For uncompressed character data, bits = characters × bits per character. Divide by 8 for bytes, then divide bytes by 1,000 for KB.

For 600 characters at 8 bits each: 600 × 8 = 4,800 bits, then 4,800 ÷ 8 = 600 bytes.

Now calculate a file containing 2,500 characters at 8 bits each. Use 1 KB = 1,000 bytes and ignore headers or other extra data.

Written answer2 marks

Show your method for calculating the 2,500-character file's size in KB.

Students type their answer here.

Fill in the blanks1 mark
The final size of this file's character data is Answer 1 KB.
Written answer3 marks

A museum stores names from many writing systems. Explain one benefit of Unicode for this database and one possible effect on text-file size.

Students type their answer here.

5. Check from memory

Distinguish the code table from the size of the file.

Written answer1 mark

State what a character set is.

Students type their answer here.