Hi Jonathan, I would guess your session files for virus capsids are large due to having alot of atoms because you have loaded many copies of the capsid protein molecule. If this is the case than Eric's suggestion to use the latest Chimera snapshot (1.2224) is your best bet. The only other options being to save fewer atoms, or use a machine with more memory. You can create the *.pyc file on a different machine with more memory that need not have interactive graphics and transfer it back to your visualization machine if necessary. The *.pyc file is platform independent (windows, mac, linux, sgi, ...). Another possible cause of large session files is if you are looking at virus models with a large number of chains. For instance I made a model of a crystal lattice of 50 copies of a small virus (satellite tobacco mosaic virus, 1a34) with asymmetric unit having 6 chains. That gave (50 capsids) x (60 asym units per capsid) x (6 chains per asym unit) = 18000 chains. The session file was about 19 Mb. There were only 3500 atoms loaded (just one asym unit) and the space in the session file for that was negligible. So the session file chews up about 1 Mbyte per 1000 multiscale chains. Unless you are making some extremely large molecular assemblies your sessions are probably mostly filled with atom data, not multiscale chain data. Thanks for making the Science cover image! I am interested in making virus architecture movies in Chimera. Here is an example using my current favorite capsid, orthoreovirus PDB 2cse: http://www.cgl.ucsf.edu/chimera/animations/movies/reovirus.mov It is in the Chimera animation gallery http://www.cgl.ucsf.edu/chimera/animations/animations.html Tom