"One complaint that many have had with Fedora in the past is the
sheer volume of updates that are provided during a Fedora
lifecycle. Almost every other day there are updates for security,
bug fixes, and enhancements. Fedora 12 takes away some of this pain
with a few changes:
* RPM packages are using XZ for compression, instead of gzip,
which allows for smaller RPM packages. Smaller packages = smaller
downloads = faster downloads.
* The presto plugin for yum that was optional in Fedora 11 is now
enabled by default in Fedora 12. So when you do download a large
number of updates, the amount you’re downloading will be
considerably smaller because presto uses RPM deltas; the deltas
only contain files that have changed, and not the entire archive.
Typically this results in about 60-80% bandwidth savings, but with
RPM now using XZ, it could result in even more (compared to a
non-presto enabled Fedora 11, for example)."