Text, Sound and Images

1. Representing Text

Why Computers Use Binary for Text

Computers work using electronic switches that can only be in two states: ON or OFF. This is why computers use the binary system – a number system that only uses two digits: 1 (representing ON) and 0 (representing OFF).

When you type text on a computer, the letters and symbols you see on the screen are not actually stored as letters. Instead, each character (letter, number, or symbol) is converted into a binary code – a unique pattern of 1s and 0s. This conversion happens because computers can only process and store information in binary form.

What is a Character Set?

A character set is a collection of all the characters and symbols that a computer system can recognize and use. Each character in the set is given its own unique binary code.

Think of a character set like a dictionary where:

• Each character (like the letter 'A' or the number '5' or a symbol like '!') is listed
• Each character has a unique binary code assigned to it
• When you type 'A', the computer looks it up in the character set and stores the binary code for 'A'

Character sets are important because they provide a standard – a set of rules that all computers agree to follow. Without this standard, one computer might interpret the binary code 01000001 as the letter 'A', while another computer might think it means something completely different. This would make it impossible for computers to communicate with each other properly.

ASCII (American Standard Code for Information Interchange)

ASCII is one of the oldest and most common character sets. It was created to provide a standard way for computers to represent text.

Key features of ASCII:

• Uses 7 bits to represent each character
• Can represent 128 different characters (because 2⁷ = 128)
• Includes:
  • Uppercase letters (A-Z)
  • Lowercase letters (a-z)
  • Numbers (0-9)
  • Common symbols (!, @, #, $, %, etc.)
  • Control characters (like Enter, Backspace, Tab)

Example: The letter 'A' in ASCII is represented by the binary code 01000001 (which equals 65 in denary).

Extended ASCII:

• Some systems use Extended ASCII, which uses 8 bits instead of 7
• Can represent 256 different characters (because 2⁸ = 256)
• Includes additional symbols like © (copyright symbol) and mathematical operators

Limitations of ASCII:

• Can only represent characters used in the English language
• Cannot represent characters from other languages (like Chinese, Arabic, Hindi, etc.)
• Cannot represent modern symbols like emojis (😊, 👍, etc.)
• Limited to a maximum of 256 characters (even with Extended ASCII)

Unicode

Unicode was created as a solution to the problems with ASCII. It was designed to represent characters from all languages around the world, not just English.

Key features of Unicode:

• Uses at least 16 bits to represent each character (some systems use 32 bits)
• Can represent at least 65,536 different characters (because 2¹⁶ = 65,536)
• Includes:
  • All ASCII characters (for backward compatibility)
  • Characters from major world languages (Chinese, Arabic, Hindi, Japanese, etc.)
  • Special symbols and mathematical characters
  • Emojis and modern digital symbols

Example: The emoji 😊 can be represented in Unicode, but not in ASCII.

Comparing ASCII and Unicode

Why Unicode uses more bits: To represent more characters, Unicode needs more unique binary codes. More bits means more possible combinations. While ASCII's 7 bits give 128 combinations, Unicode's 16 bits give 65,536 combinations – enough to include characters from many different writing systems.

Trade-off:

• ASCII = smaller file sizes but limited characters
• Unicode = larger file sizes but can represent any language or symbol