Understanding how computers handle text is crucial for anyone delving into programming, web development, or data processing. Text representation in computers is managed through various encoding systems. Among the most prominent are ASCII, Unicode, and UTF-8. This article aims to explain these systems simply and clearly.

What is ASCII (American Standard Code for Information Interchange)?

ASCII is one of the earliest encoding schemes used to represent text in computers. Developed in the early 1960s, it is a character encoding standard for electronic communication.

How ASCII Works

• 7-bit Encoding: ASCII uses 7 bits to represent each character, allowing for 128 unique characters.
• Character Set: These 128 characters include:
• Control characters (e.g., null, escape)
• Printable characters (e.g., letters, digits, punctuation marks)

Example ASCII Characters

• 'A' = 65
• 'a' = 97
• '0' = 48

What is Unicode?

Unicode is a universal character encoding standard designed to support the interchange, processing, and display of text from diverse languages and scripts across different platforms and programs.

Why Unicode?

ASCII's limitation to 128 characters meant it could not handle characters from other languages or even extended symbols and punctuation from English. Unicode was created to address this limitation, aiming to cover all the characters, punctuations, and symbols from every language in the world.

How Unicode Works

• Character Set: Unicode provides a unique number (code point) for every character, regardless of platform, program, or language.
• Code Points: These are written in the form U+xxxx, where xxxx is a hexadecimal number.
• Planes: Unicode divides its space into 17 planes, each with 65,536 code points. The most commonly used characters are in the Basic Multilingual Plane (BMP).

Example Unicode Characters

• 'A' = U+0041
• 'a' = U+0061
• '漢' (Chinese character for "Han") = U+6F22

What is UTF-8 (Unicode Transformation Format - 8-bit)?

UTF-8 is a variable-width character encoding used for electronic communication. It is capable of encoding all 1,112,064 valid character code points in Unicode using one to four one-byte (8-bit) code units.

Why UTF-8?

• Compatibility: UTF-8 is backward compatible with ASCII. ASCII characters are encoded using a single byte in UTF-8, making it efficient and compatible with systems that only support ASCII.
• Efficiency: UTF-8 uses a variable-length encoding, which means that it can use fewer bytes for characters that are used more frequently (like those in the ASCII set) and more bytes for less common characters.

How UTF-8 Works

• 1 Byte: For ASCII characters (0-127).
• 2 Bytes: For characters in the range U+0080 to U+07FF.
• 3 Bytes: For characters in the range U+0800 to U+FFFF (most of the BMP).
• 4 Bytes: For characters in the range U+10000 to U+10FFFF (outside the BMP).

Example UTF-8 Encodings

• 'A' (U+0041) = 0x41
• '€' (U+20AC) = 0xE2 0x82 0xAC
• '漢' (U+6F22) = 0xE6 0xBC 0xA2

ASCII vs. Unicode vs. UTF-8

• ASCII: Simple and efficient for basic English text. Limited to 128 characters.
• Unicode: Comprehensive, capable of representing text from any language. Not tied to a specific encoding.
• UTF-8: Efficient for representing Unicode text, especially when text primarily uses ASCII characters. Widely adopted on the web and in modern software.

When to Use Which

• ASCII: Only for legacy systems or specific situations where you know only basic English characters are needed.
• Unicode: When dealing with internationalization and text processing across multiple languages.
• UTF-8: For general-purpose encoding of Unicode text, particularly on the web and in applications supporting multiple languages.

Conclusion

Understanding ASCII, Unicode, and UTF-8 is fundamental for anyone working with text in the digital world. ASCII provides a historical foundation, Unicode offers a comprehensive solution for global text representation, and UTF-8 bridges the gap by providing an efficient, compatible encoding for Unicode. These standards ensure that text can be consistently and accurately represented, processed, and displayed across diverse platforms and languages.

Reference

1. ASCII - Wikipedia
2. Unicode - Wikipedia
3. UTF-8 - Wikipedia
4. The Unicode Consortium
5. Invisible Characters
6. Character Encoding - W3C