APT needs to be given a “list of package sources (repositories)”: the file <filename>/etc/apt/sources.list</filename> will list the different repositories(or “sources”) that publish Debian packages. APT will then import the list of packages published by each of these sources. This operation is achieved by downloading <filename>Packages.xz</filename> files or a variant using a different compression method (such as <filename>Packages.gz</filename> or <filename>.bz2</filename>) files ( (using a different compression method) in case of a source of binary packages) and <filename>Sources.xz</filename> or a variant (in case of a source of source packages) and by analyzing their contentsby analyzing their contents. In case of a source of source packages, APT downloads <filename>Sources.xz</filename> files or a variant using a different compression method. When an old copy of these files is already present, APT can update it by only downloading the differences (see sidebar <xref linkend="sidebar.apt-pdiff" />).
None
(or “sources”)that publish Debian packages. APT will then import the list of packages published by each of these sources. This operation is achieved by downloading <filename>Packages.xz</filename> files or a variantusing a different compression method (such as <filename>Packages.gz</filename> or <filename>.bz2</filename>) files ((using a different compression method) in case of a source of binary packages)and<filename>Sources.xz</filename> or a variant (in case of a source of source packages) and by analyzing their contentsby analyzing their contents. In case of a source of source packages, APT downloads <filename>Sources.xz</filename> files or a variant using a different compression method. When an old copy of these files is already present, APT can update it by only downloading the differences (see sidebar <xref linkend="sidebar.apt-pdiff" />).