Weak scaling results for Bifrost on a Silicon Graphics ICE system when running MHD with a realistic EOS and chromospheric radiation (squares), MHD with a realistic EOS, chromospheric radiation and Spitzer heat conduction (diamonds) and MHD with a realistic EOS, chromospheric radiation, Spitzer heat conduction and full radiative transport (triangles). Dashed lines show the average timing on the runs up to 256 cores.