Whats in the pool directory?
Packages are kept in a large `pool’, structured according to the name of the source package. To make this manageable, the pool is subdivided by section (`main’, `contrib’ and `non-free’) and by the first letter of the source package name. These directories contain several files: the binary packages for each architecture, and the source packages from which the binary packages were generated. You can find out where each package is placed by executing a command like apt-cache showsrc mypackagename and looking at the `Directory:’ line. For example, the apache packages are stored in pool/main/a/apache/. Additionally, since there are so many lib* packages, these are treated specially: for instance, libpaper packages are stored in pool/main/libp/libpaper/.