Character sets, ASCII and Unicode

Overview

How characters are stored, character sets and bits per character, ASCII and Unicode compared, ordered character codes worked from A = 65, and text file sizes.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   How are text characters stored by a computer?

   Model answer

   Each character is given a unique number called a character code. The computer stores that code in binary.

2. 2

   What is a character set?

   Model answer

   A character set is a defined list of characters that a computer can recognise. Each character in the set has its own binary code.

3. 3

   How does the number of bits per character limit the size of a character set?

   Model answer

   Each extra bit doubles the number of different codes available. A character set using n bits can represent 2ⁿ characters.

4. 4

   How many characters can a 7-bit and an 8-bit character set represent?

   Model answer

   A 7-bit character set can represent 128 characters. An 8-bit character set can represent 256 characters.

5. 5

   What is ASCII?

   Model answer

   ASCII is a character set covering English letters, digits, punctuation and control codes. Standard ASCII uses 7 bits, giving 128 characters.

6. 6

   Why is ASCII usually stored using 8 bits per character?

   Model answer

   Computers store data in whole bytes, so each 7-bit code is held in one byte. Extended ASCII uses all 8 bits to give 256 characters.

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