"Fedora 11 introduced a great new feature: delta RPM updates. This
feature creates delta RPM packages (.drpm) that are binary “patches” to
the existing RPM packages. Instead of downloading all files, regardless
of whether they have changed or not, a delta RPM will only download the
files that have changed compared to the previous RPM package.
Once the delta RPM is downloaded by the Presto plugin for yum, it will
try to reconstruct a full RPM based on the contents of the previous RPM,
plus the newly changed files from the delta RPM. The newly-created RPM
will then be installed by yum."