Updating indexes for block model space
When searching for a file, the file name is first converted to upper case using the upcase table (file names are case insensitive) and then hashed using a proprietary patented algorithm into a 16-bit (2 byte) hash value.
This is achieved through the introduction of a cluster bitmap and elimination (or reduction) of writes to the FAT.The feature, called Transaction Safe FAT, or Tex FAT, was granted a patent by the US patent office under US7613738 on November 3, 2009.ex FAT and the rest of the FAT family of file systems does not use indexes for file names, unlike NTFS which uses B-trees for file searching.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.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 is also supported in a number of media devices such as modern flat panel TVs, Some vendors of flash media, including USB pen drives, compact flash (CF) and solid state drives (SSD) are shipping from the factory with some of their high capacity media pre-formatted with the ex FAT file system.
For example, Sandisk ships their 256 GB CF cards as ex FAT.
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.
ex FAT can be used where the NTFS file system is not a feasible solution (due to data structure overhead), yet the file size limit of the standard FAT32 file system (viz., 4 Gi B) is unacceptable.