add note on flags NC_64BIT_OFFSET and NC_64BIT_DATA for CDF-2 and CDF-5 formats

Author: wkliao

index.html

@@ -45,9 +45,12 @@ <h2>Overview of PnetCDF</h2>
 PnetCDF is a high-performance parallel I/O library for accessing
 <a href="http://www.unidata.ucar.edu/software/netcdf/">Unidata's NetCDF</a>,
 files in classic formats, specifically the formats of CDF-1, 2, and 5.
-The CDF-5 file format, an extension of CDF-2, supports unsigned data types and
-uses 64-bit integers to allow users to define large dimensions, attributes, and
-variables (&gt; 2B array elements).
+CDF-1 is the default NetCDF classic format. CDF-2 is an extended format
+created through using flag NC_64BIT_OFFSET to support 64-bit file offsets. The
+CDF-5 file format, an extension of CDF-2 and created through using flag
+NC_64BIT_DATA, supports unsigned data types and uses 64-bit integers to allow
+users to define large dimensions, attributes, and variables (&gt; 2B array
+elements).
 </p>
 <p>
 In addition to the conventional netCDF read and write APIs, PnetCDF