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Debian (Source Control (Source Package)) Typically lower case on *nix systems. Description File DPKG-source
Debian source packages consist of two or three files. First the *.DSC file which contains some information information about the package and checksums for the remaining file(s). Second a *.TAR.GZ holding the upstream sources. And third, if any changes need to be made to the sources, they are distributed as *.DIFF.GZ. To simplify the unpacking process a single command, "dpkg-source -x *.dsc", is provided by Debian to unpack these files. This association is classified as Source Code.