Hi Jeff, Chimera keeps volume data in memory using the same numeric value types that are present in the file, for example, 32-bit float, 16-bit integer, 8-bit integer. Volume data is copied only when necessary -- for instance, using the Gaussian Filter tool creates a floating point copy of the data since Gaussian convolution of integer data produces a floating point result. Tom Jeff wrote:

does chimera store all values as float internally (even if the original map is in 2 byte integers), making the mode of the MRC file irrelevant to chimera's performance?

-jeff