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== Description ==
All computer [[operating system]]s include file copying provisions in the user interface, like the command, "[[cp (Unix)|cp]]" in [[Unix]] and "[[copy (command)|copy]]" in [[MS-DOS]]; operating systems with a [[graphical user interface]], or [[GUI]], usually provide [[copy-and-paste]] or [[drag-and-drop]] methods of file copying. [[File manager]] applications, too, provide an easy way of copying files.▼
'''File copying''' is the creation of a new '''copy [[computer file|file]]''' which has the same content as an existing file.
=== Shadow ===
Internally, however, while some systems have specialized [[application programming interface]]s ([[API]]s) for copying files (like CopyFile and CopyFileEx in [[Windows API]]), others (like Unix and MS-DOS) fall back to simply reading the contents of the old file and writing it to the new file. This makes little difference with local files (those on the computer's hard drive), but provides an interesting situation when both the source and target files are located on a remote [[file server]]. Operating systems with specialized file copying APIs are usually able to tell the server to perform the copying locally, without sending file contents over the network, thus greatly improving performance. Those systems that have no comparable APIs, however, have to read the file contents over the network, and then send them back again, over the network. Sometimes, remote file copying is performed with a specialized command, like "ncopy" in MS-DOS clients for [[Novell NetWare]].▼
There are several different technologies that use the term '''file shadowing''', but the intent of file shadowing within these technologies is to provide an exact copy (or [[Disk mirroring|mirror]] of a set) of data. For file shadowing to be effective, the shadow needs to exist in a separate physical location than the original data. Depending on the [[Disk mirroring|reasons]] behind the shadow operation, this location may be as close as a second harddrive in the same chassis or as far away as the other side of the globe.
== Use ==
▲All computer [[operating system]]s include file copying provisions in the user interface, like the command, "[[cp (Unix)|cp]]" in [[Unix]] and "[[copy (command)|copy]]" in [[MS-DOS]]; operating systems with a [[graphical user interface]], or [[GUI]], usually provide [[copy-and-paste]] or [[drag-and-drop]] methods of file copying. [[File manager]] applications, too, provide an easy way of copying files.
== Implementation ==
▲Internally, however, while some systems have specialized [[application programming interface]]s ([[API]]s) for copying files (like CopyFile and CopyFileEx in [[Windows API]]), others (like Unix and MS-DOS) fall back to simply reading the contents of the old file and writing it to the new file. This makes little difference with local files (those on the computer's hard drive), but provides an interesting situation when both the source and target files are located on a remote [[file server]].
== See also ==
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[[Category:Copyright law]]
== References ==
{{Inline citations|date=January 2018}}{{Reflist}}
* [http://www.freepatentsonline.com/5043876.html N-level file shadowing and recovery in a shared file system], United States Patent 5043876
* [http://www.freepatentsonline.com/5276871.html Method of file shadowing among peer systems], United States Patent 5276871
* [http://www.ibexpert.info/documentation/%20%209.%20IBExpert%20Services%20Menu/%20%202.%20Restore%20Database/%20%201.%20Database%20Shadow%20Files/15713.html Database Shadow Files]
== External links ==
* [https://www.gnu.org/software/emacs/manual/html_node/emacs/File-Shadowing.html Instructions on how to shadow files] for [[Emacs]]
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