Sidecar file

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Sidecar files, also known as buddy files or connected files, are computer files that store data (often metadata) which is not supported by the format of a source file.

There may be one or more sidecar files for each source file. There may also be "metadata databases" where one database contains metadata for several source files.

In most cases the relationship between the source file and the sidecar file is based on the file name; sidecar files have the same base name as the source file, but with a different extension. The problem with this system is that most operating systems and file managers have no knowledge of these relationships, and might allow the user to rename or move one of the files thereby breaking the relationship.