We have two Tridion CMS environments running with Tridion 2011 SP1. One was upgraded from 2009, the other one was a clean install.
The clean install is using all the 64 bit configuration (and dll's) where necessary. Such as TcmServiceHost.exe.config and TcmPublisher.exe.config.
On the upgrade somehow it is still using the 32 bit configs and dll's for the above two examples (TcmServiceHost_x86.exe.config and TcmPublisher_x86.exe.config).
Where and what process/config/setting in Tridion makes it use the 32 or 64 bit variant. I can't seem to figure out where exactly to look. I have a feeling that is has something to do with jar files, but which ones...