Hi Jesse, The 32-bit Linux Chimera will run on 64-bit Linux machines, and that is what we recommend. You can run either the current production release version 1.2184, the snapshot 1.2186 which has some additional features (particularly useful for density maps), or the release candidate 1.2199. I think they are all about equally stable and fast and would go with 1.2199. We have an old 64-bit Linux Chimera (version 1.2123) that I would not recommend unless you are working with very large volume data sets, bigger than 1 Gbyte. This old version will run a bit slower and is missing many new features. It was created just for use with large data sets. We do not regularly distribute a 64-bit Linux version because we do not have a machine, it is alot of work to build Chimera on new platforms, and we think there are still relatively few users who need it. That may change in the future. Tom