This article was previously published under Q100625
As part of the requirements for POSIX compliance, the Windows NT FileSystem (NTFS) provides a case-sensitive file and directory namingconvention. Even though NTFS and the POSIX subsystem each handlecase-sensitivity well, 16-bit Windows-based, MS-DOS-based, OS/2-based,and Win32-based applications do not.
In NTFS, you can create unique file names, stored in the samedirectory, that differ only in case. For example, the followingfilenames can coexist in one directory on an NTFS volume:
CASE.TXT case.txt case.TXT
However, if you attempt to open one of these files in a Win32application, such as Notepad, you would only have access to one of thefiles, regardless of the case of the filename you type in the OpenFile dialog box.
Other inconsistencies also exist. The Windows NT Command Prompt andFile Manager correctly display the names of the files. However, normalcommands, such as COPY, fail when you attempt to access one or morefilenames that differ only in case.
NTFS supports two slightly different modes of operation that can beselected by the subsystem of the application interacting with NTFS.The first is fully case sensitive and demands that file names suppliedby the application match the names stored on disk including case ifthe file on disk is to be selected. The second mode of operation iscase preserving but not case sensitive. This means that applicationscan select files on the disk even if the supplied name differs in casefrom the name stored on the disk. Note that both modes preserve thecase used to create the files. The difference in behavior noted hereapplies 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.