ASCII
Une norme de codage de caractères 7 bits associant 128 caractères à des valeurs numériques (0-127).
La structure de l'ASCII permettait des opérations binaires efficaces, la différence entre majuscules et minuscules n'étant qu'un seul bit. Bien que remplacé par Unicode, l'ASCII survit car les 128 premiers caractères d'Unicode lui sont identiques.
graph LR
Center["ASCII"]:::main
Rel_unicode["unicode"]:::related -.-> Center
click Rel_unicode "/terms/unicode"
Rel_binary["binary"]:::related -.-> Center
click Rel_binary "/terms/binary"
classDef main fill:#7c3aed,stroke:#8b5cf6,stroke-width:2px,color:white,font-weight:bold,rx:5,ry:5;
classDef pre fill:#0f172a,stroke:#3b82f6,color:#94a3b8,rx:5,ry:5;
classDef child fill:#0f172a,stroke:#10b981,color:#94a3b8,rx:5,ry:5;
classDef related fill:#0f172a,stroke:#8b5cf6,stroke-dasharray: 5 5,color:#94a3b8,rx:5,ry:5;
linkStyle default stroke:#4b5563,stroke-width:2px;
🧒 Explique-moi comme si j'avais 5 ans
Les ordinateurs ne comprennent que les nombres. L'ASCII est comme un code secret universel qui dit : 'Quand tu vois 65, dessine un A majuscule. Quand tu vois 32, fais un espace.'
🤓 Expert Deep Dive
L'ASCII véritable est strictement sur 7 bits. Les 32 premières valeurs sont des caractères de contrôle matériels (CR, LF, BEL). L'utilisation du 8ème octet a créé les pages de codes 'ASCII étendu' (comme ISO-8859-1). UTF-8 assure une compatibilité descendante parfaite avec l'ASCII 7 bits.
❓ Questions fréquentes
Why is ASCII only 7 bits instead of 8 bits?
When ASCII was developed in the 1960s, a 7-bit code was sufficient to represent the English alphabet, numbers, and punctuation. The 8th bit in a byte was often reserved as a parity bit to check for errors during data transmission over unreliable networks.
What is the difference between ASCII and Unicode?
ASCII is limited to 128 characters and primarily supports English. Unicode is a massive standard designed to support over 149,000 characters across almost every language in the world, plus emojis. However, the first 128 characters of Unicode are identical to ASCII.
What are Extended ASCII codes?
Since computers use 8-bit bytes, the 7-bit ASCII standard left the 8th bit unused (values 128-255). Different companies (like IBM, Apple, and Microsoft) used these extra 128 slots for foreign letters and drawing symbols, creating incompatible 'Extended ASCII' code pages.