ASCII 81 — Q

The uppercase letter Q (ASCII code 81) is the seventeenth letter of the modern Latin alphabet, originated from the Phoenician qoph through the archaic Greek qoppa. In English text, the letter q appears with a frequency of approximately 0.10%, making it the second rarest letter in English. Q appears almost exclusively before U in English spelling (the qu- pattern), making it one of the most predictable and constrained letters in the language.

The 26 uppercase Latin letters span ASCII codes 65 through 90, forming the capital letter block of the character set. Their placement exactly 32 code positions before the corresponding lowercase letters (97–122) was a deliberate engineering decision enabling case conversion through toggling a single bit. Uppercase letters are essential for proper nouns, sentence openings, acronyms, and programming constants. Early computing systems often supported only uppercase characters, making ASCII's inclusion of both cases a forward-looking design choice.

In the ASCII encoding table, Uppercase Letter Q is assigned code point 81 in decimal (0x51 hexadecimal, 121 octal, 01010001 binary). The 7-bit ASCII standard, first published in 1963 by the American Standards Association, defines exactly 128 characters that remain the foundation of text encoding systems worldwide. UTF-8, the dominant encoding on the modern web, is fully backward compatible with ASCII — every ASCII character is encoded as the identical single byte in UTF-8, guaranteeing that Uppercase Letter Q works reliably across all operating systems, programming languages, and internet protocols.