The first version of the netCDF file format, designed in 1988, is still supported by current software. Other netCDF format variants have been created as needed: 64-bit offset, netCDF-4, netCDF-4 classic model.

NetCDF representations:

• classic — the only format for netCDF data created between 1989 and 2004 by various versions of the reference software from Unidata. Supports the classic data model. Recently added: support for Unicode names.
• 64-bit offset — introduced in late 2004 with version 3.6 for creation of and access to much larger files. Supports only the classic data model. Works fine on 32-bit platforms. Very similar to the classic format except for use of 64-bit file offsets for start of variables. Still has size restrictions, for example 4 GiB per record for variables.
• netCDF-4 — implementation of enhanced netCDF API using enhanced HDF5 as a storage layer. Requires HDF5 1.8 or later (April 2008). Supports both classic and enhanced data model. Adds performance features as well as support for enhanced netCDF model.
• netCDF-4 classic model — variant of HDF5-based netCDF-4 format that supports only classic data model. Supports performance benefits while preserving API compatibility with netCDF-3 software.

2009 Unidata NetCDF Workshop for Developers and Data Providers > Formats and Performance