| The required file-naming construction in the DOS and Windows 3.x OSes (operating systems) was called the eight-dot-three rule. In these early PC OSes, file names were limited to a maximum of eight characters, plus an optional period (dot), followed by an
optional file extension of as many as three characters in length.
The extension served as a link or association between a software application and a file, and extensions also categorized files of the same type. For example, the .TXT extension was used for text files, and the .EXE extension denoted an executable program
file. An extension could be changed without changing the file’s format; however, the association for that type of file would then be lost. For example, if the Word file Test.doc was renamed to Test.sav, Word would no longer be associated with the file, and
therefore, attempting to open Test.sav would not automatically open the file in Word.
With the introduction of Windows 95, the eight-dot-three rule became obsolete. File names could be any length, include spaces, and use any number of periods. In addition, the file extension associations were loosened. The file type was no longer dictated
by the extension, and the extension name was hidden by default. However, with all Windows products since Win95, users can associate specific extensions with specific software applications. When the user attempts to open the file, the PC will then immediately
recognize it and load it in the appropriate program. In addition, the practice of categorizing file types by using standard extensions persists yet today. For example, .TXT (text files), .EXE (program files), .GIF (Graphics Interchange Format; graphics
files), and .DOC (Microsoft Word document files) are all standard file extensions.
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