In general, diagnostic output can be written in either 32bit unformatted IEEE or NetCDF format. In both cases, the actual writing of data is done through the I/O interface described in http://www.gfdl.gov/ vb. The option for NetCDF format is use_netCDF. If not enabled, then data will be written in 32bit unformatted IEEE.
Saving diagnostic data in NetCDF format is the preferred approach since diagnostic output is immediately accessible to visualization packages which support NetCDF. This means that there is no need to write and maintain code for manipulating diagnostic data in order to visualize it. NetCDF format also allows data to be passed between various computer platforms easily and is therefore the preferred method for sharing data.
Two options affect the efficiency of writing data. Option diagnostics_himem uses large buffers to speed up writing of data at the expense of using extra memory. Option diagnostics_lomem uses small buffers and increases computer time but uses much less memory than the former option. Option diagnostics_himem is the default.