In the original CLASS file format, any observation could have
different versions. When writing an observation to a CLASS
file, the algorithm had to reread the
observations and all their
versions already written and check if a previous version of the same
observation was already present. If yes, the version number was
increased. This is typically a
algorithm. On latest modern
computer, this started becoming a limiting factor (compared to the
OS/hardware incompressible time) when writing more than
spectra
per file (see section
).