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As described in section E-7 “FAT Configuration”, support for LFNs can be disabled, if desired. If LFNs are enabled, the application may choose to specify file names in UTF-8 format, which will be converted to 16-bit Unicode for storage in directory entries. This option is available if FS_CFG_UTF8_EN is DEF_ENABLED (see Appendix E, “Feature Inclusion Configuration” Feature Inclusion Configuration).
Entries for files that have long file names
To allow FAT to support long file names, Microsoft devised the LFN directory entry, as shown in Figure 12-4the figure below.
An LFN entry is essentially a workaround to store long file names in several contiguous 32-byte entries that were originally intended for short file names.
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