This is called a directory file set, and a 256 Mi B sub-directory can hold up to 2,796,202 file sets.
(If files have longer names, this number will decrease but this is the maximum based on the minimum three-record file set.) To help improve the sequential searching of the directories (including the root) a hash value of the file name is derived for each file and stored in the directory record.
ex FAT has been adopted by the SD Card Association as the default file system for SDXC cards larger than 32 Gi B.
Microsoft had also applied for, and so far in some cases, received additional US patents on separate components that are used within ex FAT.
Since Microsoft has not officially released the entire ex FAT specification, the Name Hash patent application is a key document in providing internal details in the understanding of the file system, since those details were revealed in Appendix A of the application.
Like NTFS and HFS , ex FAT is a proprietary file system.
Microsoft asserts that ex FAT is covered by US Patent 8583708, Quick File Name Lookup Using Name Hash, which is an algorithm used in ex FAT to speed up file searches.