Long filename

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Long filename (LFN) support is Microsoft's backward-compatible extension of the 8.3 filename (short filename) naming scheme used in MS-DOS. Long filenames can be more descriptive, including longer filename extensions such as .jpeg, .tiff, and .html that are common on other operating systems, rather than specialized shortened names such as .jpg, .tif, or .htm. The standard has been common with File Allocation Table (FAT) filesystems since its first implementation in Windows NT 3.5 of 1994.

To maintain compatibility with older operating systems, Microsoft formulated a method of generating an 8.3 filename from the long filename (for example, Microsoft.txt to MICROS~1.TXT) and associating it with the file.