File Extensions and Associations (modified 7-5-16)
See also this page for further discussion on changing associations
Naming files in Windows includes a file name and a file extension. The file extension is not normally visible in a default Windows installation. In old DOS and Windows 3.1, the rules for naming files was very restrictive.
Since Windows 95, file names can be almost anything including upper case, spaces, some punctuation and up to 255 characters.
File extensions have remained fairly consistent being normally limited to 3 characters. The difference is that in the old systems, we created our own file extensions to suit our needs. Since windows 95, the programs assign the extension and if we try to override it, we make a mess.
2016 update: File extensions can be almost anything within the DOS rules: no special characters like the / : - etc.
If you want to turn on the feature to make file extensions visible, open My Computer or Windows Explorer, Click on the menus and look for options or Folder Options. Each version of Windows has changed the location and name. You should get a dialog box that is titled Folder Options. Click the View tab and find the box that says "Hide File Extensions For Known File Types" and click the box to remove the check. If it is already unchecked, leave it.
In Windows 10 the menu at ther top of the Explorer window has a selection called View. Selecting that shows some boxes. If checked the item is selected. If blank you need to check it.
The danger in having the extensions visible is this: If you change a file name, you must also include the correct extension. If you leave the option to hide extensions, then the extension is automatically added to a changed file name. Again since about windows 7, when you choose to rename a file, the extension does not change. BUT CAUTION: If you highlight the entire file name and extension, it can be lost.
What is the purpose of an extension? Windows has a registered association between the file extension and the program it is associated with. For example, a .doc file is associated with either WordPad or Word. A .txt is associated with Notepad. If you ask the computer to open a file with a known extension (By double clicking it), Windows will automatically open the correct program and open the file in that program.
You can view the file associations currently in use by opening the folder options discussed above and clicking on the File Types tab. You will see a list programs and their associated extensions. Windows Me has changed the appearance of the dialog box, but the information is still there.
These associations can be changed. The easiest way to do it is to find a file with the extension to be associated with a different program, and Right Click on the file name. Choose "Open With" from the menu. Scan through the list of programs in the Open With dialog box and select the one you want. If you want the change permanent, also check the "Always use this program..."
The biggest problem we have today is graphics files. Every time you install a new graphics program, the new program assumes control over all the graphic extensions. Then if you decide to uninstall it, the extensions are orphaned and windows does not know how to open them. You then get a dialog box that says "Open With" and shows a list of programs. Just choose a program from the list. Be sure it is one that will handle the file type.
For detailed instructions on changing file associations, Click Here.
.2GR APPLIED TO Win 3x on 286 or 386 computers
For a discussion of what files can be deleted to cleanup your hard drive, click here
See this page for additional discussion of e-mail virus problems.
Some well known viruses transmit themselves in a form that appears
to be a picture file, like OPENME.JPEG.vbs. People often don't see
the final .vbs and assume the attachment is a safe picture. It's not.
According to Microsoft, files ending with the extensions shown in
the list below can contain executable code,
and contain a virus.
Microsoft Access project
The pages below reflect a quick search on Google for sites with extensive lists of File Extensions. Still valid in 2016
Note: this site is provided free. Donations are accepted to help support the
work. Click here for instructions.