The file extension (filename extension), also known as the file suffix, is a mechanism used by the operating system to mark file types. Typically, an extension follows the main file name, separated by a delimiter. The extension can be thought of as metadata for a type.(Recommended learning:phpstorm)
The file extension (Filename Extension, or extended file name, suffix name) is an early operating system (such as VMS/CP/ M/DOS, etc.) is a mechanism used to mark file formats.
In terms of DOS, a file extension follows the main name of the file and is separated by a delimiter. In a file name like "example.txt", example is the file main name, txt is the file extension, indicating that the file is a plain text file, and the period "." is the separator between the file main name and the file extension.
DOS operating systems (including Windows 3.x) limit file extensions to 3 characters.
Personal computers (PC) have been on other Windows operating systems since Microsoft launched Windows 95, whether it is 16/32-bit Windows 95, Windows 98, Windows ME or 32-bit Windows NT, Windows 2000, Windows XP, Windows 2003 and Windows Vista.
The FAT32 file system of Windows 7 contains an interface-level correction so that the number of characters in the file extension can reach 256 English characters (long file name), but at the system level, the 3-letter length is still retained. naming scheme, which is invisible to many users. The NTFS file system does not have this limitation.
In the long file name state, the file extension can be displayed or hidden depending on the shell or browser settings.
This also allows malicious users interested in spreading computer viruses or worms to disguise LOVE-LETTER-FOR-YOU.TXT.vbs or JustForYou.TXT.exe to look harmless Plain text files (LOVE-LETTER-FOR-YOU.TXT or JustForYou.TXT) can deceive target users.
If the file extension is hidden, then the VBScript file or executable file containing a computer virus may trick the user into opening and running it without warning.
This naming method has major flaws, and even security flaws, so some operating systems no longer follow the file extension specifications, but use more precise file magic numbers (magic numbers). Determine the file type (see UNIX/Linux systems). However, the Windows series operating systems, even the latest Windows 10, still maintain this naming format.
The more important function of the file extension is to let the system decide which software to use when the user wants to open the file. For example, in the Windows system, the exe file is an executable file, and the doc file uses Microsoft by default. Word files opened by Word.
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