1347. What are the .doc and .xls at the end of a file name?

Where are My File Extensions?

I recently upgraded to Windows 8. Why do files no longer include letters after a period at the end of their names? I used to see file names that ended with .doc and .xls, and even longer names like .docx and .xlsx. What does this information mean, and do I need to do about this? And why do I no longer see this part of the file name?

Back in the “old days”, operating systems used a three-letter file extension (like .doc or .xls) to indicate to the operating system an association between the file and the application that you needed to run in order to work with the data file. Every different application that handled data files needed to specify its own distinct three-letter file name extension. For example, Microsoft Word files had a .doc extension, and Excel files had a .xls extension. If two applications attempted to share the same file extension for their data files, confusion was destined to occur. (You can find a possibly too-complete list of standard file extension associations at this site: http://whatis.techtarget.com/file-extension-list). Operating systems for both PCs and Macs shared this functionality.

As time went on, modern operating systems relied less and less on the file extensions, and the number of letters allowed in the file extensions grew, and it became possible to include more than one period in file names. (For example, a file name like MyDataFile.this.is.my.special.data.docx is perfectly legal in current versions of Windows.)

Although Windows and OS X handle file extensions slightly differently, one fact is certain: In a graphical environment, as in any modern operating system, seeing the file extension is far less important than it once was, because both Windows Explorer and Finder display an icon indicating the file type next to the file. In each case, you see an icon corresponding to the default application associated with the data file. In both Windows and OS X, you can change the default association, so that clicking on a file with a particular file extension runs a specific program, which might be different than the default association. (For example, you could convince Windows to run Wordpad, rather than Microsoft Word, when you click a .doc file.)

Most importantly, you can show or hide file extensions on both PCs and Macs. The steps differ, based on the particular version of the operating system. Search the web for “show file extensions” followed by your operating system (Windows 7, or OS X 10.8, for example), and you’ll find the instructions you need.

Finally, you asked why this changed when you installed Windows 8? In your previous operating system had been set to display file extensions, and by default, Windows 8 does not. You can, of course, display them by following the online instructions (both of us are accustomed to seeing file extensions, so always display them in every operating system).