2.2.1.
Overview of Debian packages
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Packages generally contain all of the files necessary to implement a set of related commands or features. There are two types of Debian packages:
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Binary packages, which contain executables, configuration files, man/info pages, copyright information, and other documentation. These packages are distributed in a Debian-specific archive format (see Debian package format, Section 2.2.2); they are usually distinguished by having a .deb file extension. Binary packages can be unpacked using the Debian utility
dpkg; details are given in its manual page.
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Source packages, which consist of a .dsc file describing the source package (including the names of the following files), a .orig.tar.gz file that contains the original unmodified source in gzip-compressed tar format, and usually a .diff.gz file that contains the Debian-specific changes to the original source. The utility
dpkg-sourcepacks and unpacks Debian source archives; details are provided in its manual page.
Installation of software by the package system uses "dependencies"
which are declared by the package maintainers. These dependencies are
documented in the control file associated with each package. For
example, the package containing the GNU C compiler (gcc) Depends
on the package binutils which includes the linker and assembler.
If a user attempts to install gcc without having first installed
binutils, the package management system (dpkg) will print an error
message that it also needs binutils, and stop installing
gcc. (However, this facility can be overridden by the insistent
user; see dpkg(8).) For additional details, see Package dependencies, Section 2.2.8 below.
Debian's packaging tools can be used to:
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manipulate and manage packages or parts of packages,
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aid the user in the splitting of packages that must be transmitted through a limited-size medium such as floppy disks,
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aid developers in the construction of package archives, and
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aid users in the installation of packages which reside on a remote Debian archive site.

