isr.co.ro : glossary Case Sensitive Said of programs and systems that treat capital and lowercase letters as different characters--for example, where "DIR" is not accepted as the same command as "dir." For historical reasons, the Unix operating system and most of its derivatives are case sensitive, while the MS-DOS operating system and the Macintosh are not. Similarly, most multiuser application programs based on Unix are case sensitive, while most software designed for personal computers is not. Since the Internet has inherited features from a wide variety of systems, some of its features are case sensitive. If you find that a typed-in command doesn't work or a filename doesn't produce a match when it appears it should, you may find the cause is a case mismatch.