Filename extensions indicate a file’s type and compatible programs. Operating systems use them to recognize different files, but newer systems can identify files through data. “8.3” is a common system with eight characters for the name and three for the extension. Some systems don’t require extensions and identify files based on data. Extensions can be hidden, so programs often display them by default to avoid viruses.
A filename extension is part of a computer file name that has traditionally been used to indicate the type of file and potential programs that can be used to open or run that file. The system used for filename extensions usually depends on the operating system (OS) a person is using, and some types of operating systems do not use filename extensions at all. Extensions are usually identified as the last part of a file name and are usually separated from the file name by a period. A filename extension is commonly short, often just three letters, and is often used as a name to refer to a particular type of file.
Also sometimes called a file type, a file name extension is typically used by the operating system on a computer to correctly recognize different types of files. This has only been done in certain types of operating systems in the past, although newer types of operating systems often have the ability to recognize different files through the data included in the file itself. New types of operating systems will continue to use file name extensions for computer files often, however, to ensure backward compatibility and to remain familiar to users of older computers. However, sometimes these systems are unnecessary and a filename extension can also be used for malicious reasons.
One of the most common forms of filename extension has been a system often referred to as “8.3” or “basename.ext”. Older types of computer operating systems often only allowed up to eight characters for the file name, followed by a three-character extension. This is the source of the 8.3 name, as well as the name “basename.ext”, which includes a base name of only eight characters and “.ext” to indicate a three-character extension. There are many popular and common types of file extensions such as “.txt” for text files, “.jpg” for JPEG or image files, and “.mp3” for MPEG version three files.
Some types of operating systems do not require a filename extension for a file and often identify files based on data included elsewhere in the file. There are also extensions of different sizes such as “.html” for Hypertext Markup Language (HTML) files. Modern systems typically allow users to indicate which program is used to open which files, either by default or by choosing when opening a file.
Some types of programs have extensions that are hidden from users, so a virus with a name like “basename.txt.EXE” may be created, and only “basename.txt” will be displayed. This would appear to be a harmless text file to users, when in reality it would be an executable file that could install a virus on a system. To avoid this, most programs will display a filename extension by default or allow users to display it if they choose.
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