Emerge config file needs updating
If this is the case, the system should first receive older Portage tree snapshots and upgrade at least Portage (but preferably all packages in the system set), gradually increasing the Portage tree snapshot date until it is recent enough to follow the profile switching instructions again: Older snapshots are often still available on some mirrors on the Internet or on specific locations dedicated for this purpose.
Most architectures now also default to the 2.6 kernel tree where 2.4 was chosen previously.
Ideally, users install software once and never bother with releases: just follow the instructions in A Portage introduction in the Gentoo handbook that explain how to keep the system up to date.
While that's the way things usually go, sometimes changes are made to the core system which require updates to be done manually.
to unmask a 2.6 version of sys-kernel/gentoo-sources and a full rebuild.
All other archs - There are no fundamental changes in this profile. To switch to the 2005.1 profile, point the - With the 2005.1 release, the ppc and ppc64 profiles were merged and a number of subprofiles for specific subarchitectures were created.
There are some subprofiles available for G3 and G4 processors, and G3/Pegasos and G4/Pegasos for the Pegasos Open Desktop Workstation.