Comparing ASCII and Unicode

ASCII and Unicode are both character sets: lists of characters, each with its own binary code. They differ in the range of characters they cover, how many bits each character uses, and how much storage the same text needs.

Feature	ASCII	Unicode
Range of characters and languages	English letters, digits, punctuation and common symbols.	Writing systems from around the world, plus many extra symbols and emoji.
Bits per character	8 bits, giving 256 possible codes.	More than 8 bits, often 16 bits, giving 65,536 possible codes.
Effect on file size	Each character takes 8 bits, so English text stays small.	Each character takes more bits, so the same text takes more storage.

ASCII's 256 codes are enough for English text, but they cannot cover every character used around the world. Unicode has many more possible codes, so it can store text in other writing systems, as well as symbols and emoji that ASCII has no code for. If a character is not in a character set, that set cannot store it.

The extra range has a cost. Because Unicode generally uses more bits for each character, a piece of text stored in Unicode takes more storage than the same piece stored in ASCII. Think of ASCII as a small English-only phrasebook and Unicode as a large multilingual dictionary: the larger book covers far more, but it takes up more shelf space. The text looks the same on screen, but its Unicode file is bigger.

That trade-off is why both are still used: ASCII keeps English text compact, while Unicode lets you store text in any writing system, or symbols such as emoji, at the cost of more storage for the same number of characters.

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