 exFAT employs a filename hash-based lookup phase to speed certain cases, which is described in US Patent 8321439, "Quick File Name Lookup Using Name Hash", which document perhaps contains additional details helpful in understanding of the file system, in Appendix A.Like NTFS, exFAT can pre-allocate disk space for a file by just marking arbitrary space on disk as 'allocated'.For each file, exFAT uses two separate 64-bit length fields in the directory