Sidecar file

<h2 id="examples">Examples</h2>
Amiga Hunk metadata
In <a href="/facts/AmigaOS/1E2k1fuN">AmigaOS</a>, a file with a .info <a href="/facts/File_extension/cJgfAym4">extension</a> contains metadata for a companion <a href="/facts/Amiga_Hunk/DhovjzPD">Amiga Hunk</a> <a href="/facts/Executable_file/VSst9eLA">executable file</a>.
Extensible Metadata Platform
<a href="/facts/Extensible_Metadata_Platform/5KjPybyN">Extensible Metadata Platform</a> (XMP) metadata is stored in a sidecar file when either a <a href="/facts/File_format/qrXbwJaH">file format</a> does not support embedded XMP metadata or if the workflow requires this.
DxO sidecar
Similar to the XMP format, DOP sidecars store metadata and edits made through DxO PhotoLab<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> and other DxO tools<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a>
Connected Web Files and Folders
A <a href="/facts/File_system/FdPm90uc">file system</a> object that associated two or more files. The file system treats connected files as a unit for purposes of moving, copying, and deleting. Some versions of <a href="/facts/Internet_Explorer/uL8a4Y5l">Internet Explorer</a> and <a href="/facts/Microsoft_Word/HPSu5W4j">Microsoft Word</a> can save an HTML and its hyperlinked assets as such a unit.
THM
Many digital cameras will store a .thm (thumbnail) file alongside a recorded movie, with the same base filename as the movie file. These thumbnail files are <a href="/facts/JFIF/fxl3q2CE">JFIF</a>-encoded image files. This system allows for quickly displaying a still preview of the movie, and storing camera data which is not supported by the AVI file format.
INF
Acorn filesystems support metadata such as load and execution addresses that may not be natively supported on other filesystems. A .inf file is used to store this metadata in text format, stored in a file with the same base filename, e.g. Menu and Menu.inf, Build.src and Build.src.inf.
JPEG + WAV
Some digital cameras allow for voice/audio annotations with photos. These are then stored as <a href="/facts/WAV/ptUfKleW">WAV</a> audio files alongside the <a href="/facts/JPEG/HQ8QS3uB">JPEG</a> photo file, with the same base filename.
PDF + annotations
<p>PDF viewers which allow the reader to annotate documents with comments and drawings may store these in a sidecar file, such as <a href="/facts/Xournal/g8ee7rye">Xournal</a>'s .xoj files.
</p>
RunPacker
The MS-DOS-based <a href="/facts/Self-extracting_archive/xTq54ltw">self-extracting archive</a> generator <i>RunPacker</i> relied heavily on sidecar files because the proprietary package format PFA (packfile archive) used in it did not natively store <a href="/facts/File_attribute/eVga2BAu">file attributes</a> or <a href="/facts/Timestamp/6lApANE6">timestamps</a>. To address this limitation, a <a href="/facts/Backward_compatibility/FbHFBu5y">backward-compatible</a> system of <i>auxiliary files</i> (as called in official documentation) was implemented to store aforementioned data in volumes without changing their format. These were added to the PFA volume the same way as ordinary files, except they were marked by special characters in their name, and software made aware of this system (sometimes called ePFA, <i>Extended PFA</i>) processed them <a href="/facts/Transparency_(human%25E2%2580%2593computer_interaction)/XpkuWzX6">transparently</a>. Older programs relying on the PFA format would simply read or extract the file along with all others found in the volume. The ePFA format was designed with further extensibility in mind, and has been actually extended with several features over time.
Meta Information Encapsulation (MIE)
<a href="/facts/Meta_Information_Encapsulation/9MQeMuP3">Meta Information Encapsulation</a> sidecar files. The MIE format is an extensible, dedicated meta information format part of <a href="/facts/ExifTool/9MQeMuP3">ExifTool</a>. MIE files can be used to encapsulate meta information from many sources and bundle it together with any type of file.
<p>A variation of this are copies of the source file which contain largely the same information, but in a different format or from a previous version:
</p>
Exif
Since many JPEG editing software used to destroy <a href="/facts/Exif/KHFgGnk6">Exif</a> metadata stored in digital photos, some photo cataloging applications can extract the Exif data and store that in an .exf file, so that the metadata can later be re-inserted into the JPEG file.
Raw + JPEG
Many digital cameras allow to store both uncompressed <a href="/facts/Raw_image_format/1T6qygdz">raw</a> data and a <a href="/facts/Jfif/fxl3q2CE">JFIF</a>-encoded image file when shooting in raw mode. This allows for faster previewing the photo, and support by applications that do not support the (often undocumented) raw format.
TIF + TFW or JPG + JGW
Aerial photos may be supplied with a <a href="/facts/World_File/Gs2LSHYR">World File</a> that determines the location, size and rotation of the image.
<h2 id="alternatives">Alternatives</h2>
<p>Rather than storing data separately, it can be stored as part of the main file. This is particularly done for <a href="/facts/Digital_container_format/mSfwwdSA">container files</a>, which allow certain types of data to be stored in them. Instead of separate files on the file system, multiple files can be combined into an <a href="/facts/Archive_file/u7BIXv7D">archive file</a>, which keeps them together, but requires that software processes the archive file, rather than individual files. This is a generic solution, as archive files can contain arbitrary files from the file system.
</p>
<h3>Forks</h3>
<p class="note">Main article: <a href="/facts/Fork_(file_system)/B1QFYk2t">Fork (file system)</a></p>
<p>A file system level solution for the same problem are <i><a href="/facts/Fork_(file_system)/B1QFYk2t">forks</a>,</i> which allow multiple pieces of data to be associated with a single file. Sidecar files can be seen as "forks for file systems without native support for forks".
</p><p>These can then be manipulated with usual file system tools: because the support is built into the operating system, these <a href="/facts/Resource_fork/zVnSVjbb">resource forks</a> will not show up as separate files, and all applications inherit support for resource forks. However, forks cannot be copied to file systems without support for forks, or transmitted over a channel that does not support forks. For interchange forks are generally instead stored as sidecar file.
</p><p>The <a href="/facts/Classic_Mac_OS/I5fQq44K">classic Mac OS</a> and <a href="/facts/MacOS/Y93vVpTm">macOS</a> are notable examples of operating systems with support for forks, in the <a href="/facts/Hierarchical_File_System_(Apple)/FVv6r1pe">HFS</a> file system. However, this causes problems with exchanging over <a href="/facts/ISO_9660/zAEVMFnu">ISO 9660</a> format <a href="/facts/CD-ROM/JwuaYLJv">CD-ROM</a>, <a href="/facts/File_Allocation_Table/uFvpmWxa">FAT</a> format <a href="/facts/MS-DOS/fVrrz1uN">MS-DOS</a> disks, and over internet email, and requires the use of sidecar files to store this information. Microsoft <a href="/facts/NTFS/dryNM3BK">NTFS</a> supports Alternate Data Streams which are similar.
</p>

<ul><li><a href="https://web.archive.org/web/20120321193523/http://www.windowsitpro.com/article/tips/jsi-tip-3841-what-is-the-windows-2000-connected-file-feature-">Windows IT Pro - What is the Windows 2000 Connected File feature?</a></li>
<li></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"DxO PhotoLab 7 : Le logiciel complet de traitement de photos RAW". <a href="https://www.dxo.com/fr/dxo-photolab/" target="_blank">https://www.dxo.com/fr/dxo-photolab/</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"Metadata Management Support". 16 October 2021. <a href="https://tutodxo.com/en/metadata-management-support/" target="_blank">https://tutodxo.com/en/metadata-management-support/</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
</ol>

Sidecar file open-in-new

Sidecar file