Filenames are Case Sensitive on NTFS Volumes

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In NTFS, you can create unique file names, stored in the same directory, that differ only in case. For example, the following filenames can coexist in one directory on an NTFS volume: However, if you attempt to open one of these files in a Win32 application, such as Notepad, you would only have access to one of the files, regardless of the case of the filename you type in the Open File dialog box.

Other inconsistencies also exist. The Windows NT Command Prompt and File Manager correctly display the names of the files. However, normal commands, such as COPY, fail when you attempt to access one or more filenames that differ only in case.

NTFS supports two slightly different modes of operation that can be selected by the subsystem of the application interacting with NTFS. The first is fully case sensitive and demands that file names supplied by the application match the names stored on disk including case if the file on disk is to be selected. The second mode of operation is case preserving but not case sensitive. This means that applications can select files on the disk even if the supplied name differs in case from the name stored on the disk. Note that both modes preserve the case used to create the files. The difference in behavior noted here applies only when an application needs to locate an existing file. POSIX takes advantage of the full case sensitive mode, while MS-DOS, WOW, and Win32 subsystems use the case insensitive mode.