isr.co.ro : glossary Case insensitive Said of programs or systems that accept uppercase and lowercase letters as equivalents in commands, file names, parameters, and other values. Programs of this type accept DIR and dir as equivalent commands. But because of obscure historical reasons, the Unix system and features of the Internet derived from Unix are instead sensitive to case. Most usernames and passwords, for example, are case sensitive. Most programs based on MS-DOS, Windows, or the Macintosh operating system are not.