This significantly reduces the CPU cycles because most file names are more than 2 characters (bytes) in size and virtually every comparison is performed on only 2 bytes at a time until the intended file is located.
ex FAT introduces metadata integrity through the use of checksums. The Volume Boot Record (VBR) is a 12 sector region that contains the boot records, BIOS Parameter Block (BPB), OEM parameters and the checksum sector.
A single bit in the directory record indicates that the file is contiguous, telling the ex FAT driver to ignore the FAT.
This optimization is analogous to an extent in other file systems, except that it only applies to whole files, as opposed to contiguous parts of files.
ex FAT was first introduced in late 2006 as part of Windows CE 6.0, an embedded Windows operating system.
Most of the vendors signing on for licenses of ex FAT are either for embedded systems or device manufacturers that produce media that will be preformatted with ex FAT.
(There are two VBR type regions, the main VBR and the backup VBR.) The checksum sector is a checksum of the previous 11 sectors, with the exception of three bytes in the boot sector (Flags and percent used).
This provides integrity of the VBR by determining if the VBR was modified. Any corruption in the table could prevent files from being located because this table is used to convert the filenames to upper case when searching to locate a file. Multiple directory records are used to define a single file and this is called a file set.
ex FAT has been adopted by the SD Card Association as the default file system for SDXC cards larger than 32 Gi B.When a file is accessed, the directory must be sequentially searched until a match is found.For file names shorter than 16 characters in length, one file name record is required but the entire file is represented by three 32-byte directory records.The most common cause could be a boot sector virus, but this would also catch any other corruption to the VBR. This file set has metadata including the file name, time stamps, attributes, address of first cluster location of the data, file lengths, and the file name.A checksum is taken over the entire file set and a mismatch would occur if the directory file set was accidentally or maliciously changed.Microsoft had also applied for, and so far in some cases, received additional US patents on separate components that are used within ex FAT.