Yum usually works by checking which Fedora release version is installed. I would imagine that the preupgrade package downloads and installs the new fedora-release package for you. A yum upgrade command is then run which upgrades all F12 software to F13. This is an automatic way of doing what we had to do manually before the preupgrade package was introduced.
Here's a historical document
showing the old way of doing it.
The upgrade file is called preupgrade.
So when you run preupgrade
, the preupgrade package downloads fedora-release and both would be stored under /var/cache/yum/i386/12/fedora/packages on a 32 bit machine.
Whether they will be there after the upgrade is questionable as I expect it runs yum clean all
when it has finished. This removes all temporary packages.