One of the major change in CLASS90 is the new way OTF data are stored. While advantages have already been described, the main inconvenient is an increase of the size of the data on disk and RAM memory by at most 20-30%, due to the new individual headers (Note that this increase becomes negligible for spectra with a large number of channels).
Data access time is less problematic as the data has always been buffered by CLASS. In fact, we choose this OTF data format to have a much more user-friendly approach to OTF processing. Indeed, it maybe (but still has to be proven...) that the CPU time will be a bit larger with CLASS90 than with CLASS77 for perfect data. However, our main goal is to decrease the human time spent on data reduction to deal with the unavailable problems.