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XCFiles from Datalight is a proprietary, full-featured implementation, intended to be portable to bit systems. Technical specialities[ edit ] File name lookup[ edit ] exFat employs a filename hash-based lookup phase to speed certain cases, which is described in US Patent Quick File Name Lookup Using Name Hash, which document perhaps contains additional details helpful in understanding of the file system, in Appendix A.
File and cluster pre-allocation[ edit ] 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 bit length fields in the directory: To provide improvement in the allocation of cluster storage for a new file, Microsoft incorporated a method to pre-allocate contiguous clusters and bypass the use of updating the FAT table and on December 10, the US patent office granted patent US 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 byte directory records. This is called a directory file set, and a MiB sub-directory can hold up to 2, 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.
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 bit 2 byte hash value.
Each record in the directory is searched by comparing the hash value.
|Sphinx | Open Source Search Server||Direct use means the ability to access and update data in a "native" storage format without intermediate format translations in an environment e.|
When a match is found, the file names are compared to ensure that the proper file was located in case of hash collisions. This improves performance because only 2 bytes have to be compared for each file.
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. Metadata and checksums[ edit ] exFAT introduces metadata integrity through the use of checksums.
There are three checksums currently in use. 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.
The most common cause could be a boot sector virus, but this would also catch any other corruption to the VBR. A second checksum is used for the upcase table. This is a static table and should never change. 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.
The third checksum is in the directory file sets. Multiple directory records are used to define a single file and this is called a file set. 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. When the file system is mounted, and the integrity check is conducted, these hashes are verified.
Mounting also includes comparison of the version of the exFAT file system by the driver to make sure the driver is compatible with the file system it is trying to mount, and to make sure that none of the required directory records are missing for example, the directory record for the upcase table and Allocation Bitmap are required and the file system can't run if they are missing.
If any of these checks fail, the file system should not be mounted, although in certain cases it may mount read-only. The file system provides extensibility through template based metadata definitions using generic layouts and generic patterns.
This lack of documentation hampered the development of free and open-source drivers for exFAT.
Accordingly, exFAT support was effectively limited to Microsoft's own products and those of Microsoft's licensees, which in turn inhibited exFAT's adoption as universal exchange format.
Interoperability requires that certain results be achieved in a particular, predefined way an algorithm. For exFAT, this potentially requires every implementation to perform certain procedures in exactly the same way as Microsoft's implementation.
Some of the procedures used by Microsoft's implementation are patented, and these patents are owned by Microsoft. Regardless of whether open-source or not including Samsung's leaked kernel driver source that was initially fraudulently rebadged as GPL-licensed  according to Microsoft "a license is required in order to implement exFAT and use it in a product or device.
It may also be possible to achieve the intended results without infringing Microsoft's patents.Practical Abstract Examples. Getting into college is a huge achievement; still, it comes with some strings attached.
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Since a GeoPackage is a database container, it supports direct use. This means that the data in a GeoPackage can be accessed and updated in a "native" storage format without intermediate format translations.