Input (grade 13): Lowercase "o" for "octet" is a commonly used symbol in several non-English-speaking countries, and is also used with metric prefixes (for example, "ko" and "Mo").
Output (grade 10): Sometimes it is incorrectly abbreviated as lowercase "b"; lowercase "b" is the abbreviation for "bit". For example, "MB" means "Megabyte" and "Mb" means "Megabit".