File copying

In digitalfile management,copyingis afile operationthat creates a newfilewhich has the same content as an existing file. Computeroperating systemsinclude file copying methods to users; operating systems withgraphical user interfaces(GUIs) often providingcopy-and-pasteordrag-and-dropmethods of file copying. Operating systems may have specialized file-copyingAPIsare usually able to tell the server to perform the copying locally, without sending file contents over the network, thus greatly improving performance.

Description

File copyingis the creation of a newcopyfilewhich has the same content as an existing file.

Shadow

There are several different technologies that use the termshadowing,but the intent of shadowing within these technologies is to provide an exact copy (ormirrorof a set) of data. For shadowing to be effective, the shadow needs to exist in a separate physical location than the original data. Depending on thereasonsbehind the shadow operation, this location may be as close as the BIOS chip to the RAM modules, a second harddrive in the same chassis, or as far away as the other side of the globe.

Use

All computeroperating systemsinclude file copying provisions in the user interface, like the command, "cp"inUnixand "COPY"inDOS;operating systems with agraphical user interface,orGUI,usually providecopy-and-pasteordrag-and-dropmethods of file copying.File managerapplications, too, provide an easy way of copying files.

Implementation

Internally, however, while some systems have specializedapplication programming interfaces(APIs) for copying files (like CopyFile and CopyFileEx inWindows API), others (like Unix and 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 remotefile 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 DOS clients forNovell NetWare.TheCOPYcommand in some versions ofDR-DOSsince 1992,has built-in support for this. An even more complicated situation arises when one needs to copy files between two remote servers. The simple way is to read data from one server, and then to write the data to the second server.

See also

• Computer file § Moving methods
• Core dump
• Soft copy
• Hard copy
• List of file copying software
• ln (Unix)
• NTFS junction point
• Zero copy

Further reading

• N-level file shadowing and recovery in a shared file system,United States Patent 5043876
• Method of file shadowing among peer systems,United States Patent 5276871
• Database Shadow Files

External links

• Instructions on how to shadow filesforEmacs