Recently Debian's apt-get received a feature that many were awaiting; the ability to download incremental updates to the Packages file in a given repository. The files are downloaded as *.pdiff and applied one by one to the Packages file.
Unfortunately, the pdiff merging process is extremely slow on a lower-end computer. This behavior can be disabled by adding the following line to your local apt.conf (or placed into a file dropped into apt.conf.d):
Acquire::PDiffs “false”;