Friday, March 30, 2012

What is VFAT?

VFAT (Virtual File Allocation Table)
VFAT is an important part of operating system after Windows 95/98, mainly used for dealing with long file name which can not be disposed by FAT system. File Allocation Table is a table of the saved file marked in the storage location on disk. The filename in the original DOS operating system must be less than 8 characters, and it is a limitation for users. The function of VFAT is similar to a driver. It runs under protected mode and uses VCACHE to cache.

One of user experience target of designer of Windows 95 is to use long file name in the new operating system aside from the traditional 8.3 file name. LFN is achieved in a work area by ranking directory entry (see instruction below). According to naming rule of Windows 95VxD device driver, the new expanded file system is called VFAT.
Interestingly, VFAT drive is used in Windows for Groups 3.11, earlier than Windows 95.But it is used in the 32 bit file access, which is a file management system with its own high-performance protected mode bypassing DOS. BIOS or better 32 bit disk access can be used directly, such as windows with its own protected mode disk drive. It is a back door. Microsoft advertised that the 32 bit file access was based on "Project of Chicago 32 bit file access". In Windows NT, the support of FAT file system to LFN started from 3.5 edition.

Third-party support
Other IBM PC Optional operating systems such as Linux, FreeBSD and BEOS are in support of FAT form, and most of them also quickly support VFAT and FAT32 form after release of corresponding Windows version. The early edition of Linux includes UMSDOS form which is stored as an independent FAT called Linux with Unix file attributes(such as long file name and access permission).UMSDOS was stopped after the release of VFAT, and the function was forbidden since the use of core 2.5.7. Besides startup disk, the other volumes are also in support of FAT file system.

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