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NetCDF has changed (and improved) over its lifetime. That means the user must have some understanding of netCDF versions.
To add to the confusion, there are versions for the APIs, and also for the data files that they produce. The API version is the version number that appears in the tarball file that is downloaded from the netCDF website. For example the current version is 3.6.2.
Since version 3.6.0 there are two versions of the netCDF file format. Both underlying formats are accessed by the same netCDF API, but are stored differently on disk. The formats are called “classic format,” and “64-bit offset format.”
The good news is that all netCDF files ever written can always be read by the latest netCDF release. That is, we guarantee backward data compatibility.
As long as you have a version of netCDF greater than 3.6.0, you can use either format. To share data in 64-bit offset format, everyone who wants to read the data must use at least version 3.6.0.
The default format is classic format. To get 64-bit offset format, set a flag when creating the file. For more information about the format, see Format.
Classic format has some strict limitations for files larger than two gigabytes. (see NetCDF Classic Format Limitations).
64-bit offset is very useful for very large data files (over two gigabytes), however these files can only be shared with those who have upgraded to version 3.6.0 (or better) of netCDF. Earlier versions of netCDF will not be able to read these files.