?Q? – files that are compressed, often by the SQ program. While MS-DOS and NT always treat the suffix after the last period in a file's name as its extension, in UNIX-like systems, the final period does not necessarily mean that the text after the last period is the file's extension.
Some filenames are given extensions longer than three characters. Examples of operating systems that do not impose this limit include Unix-like systems, and Microsoft Windows NT, 95- 98, and ME which have no three character limit on extensions for 32-bit or 64-bit applications on file systems other than pre-Windows 95 and Windows NT 3.5 versions of the FAT file system. Many operating systems do not limit filenames to one extension shorter than 4 characters, as was common with some operating systems that supported the File Allocation Table (FAT) file system. Filename extension it is usually noted in parentheses if they differ from the file format name or abbreviation. This is a list of file formats used by computers, organized by type.
You can help by adding missing items with reliable sources. This is a dynamic list and may never be able to satisfy particular standards for completeness.
