Question: Is there a place or book, which defines all those arcane extensions such as .PAB, .PST, .CFG, .DFL, .FCO, .EM, .8BI, etc., etc., and gives some indication whether files with the different extensions can be eliminated if not used? “â€J.T.
Answer: File extensions are one of the many legacies of MS-DOS that continue to plague some of even the most advanced users. MS-DOS was Microsoft Disk Operating System, the precursor to Windows. They came about because, under DOS, there was a rule that all file names had to follow the 8.3 rule. In other words, they could be named with up to eight characters then a period or “dot” (.). The three characters that followed the name and the dot were used to identify the file’s type. Just as people have last names that identify their family, a file extension explains what file family the file comes from.
Since Windows 95 came out, the 8.3 rule has become obsolete”â€you can give files long names and even use spaces, though the extensions are still used to identify file types.
There are quite a few websites that list file types. One of the better ones is called “Every file format in the world”, and can be found at http://whatis.com. It’s a good place to start.
There’s also a list of programs on the aforementioned page that will automatically identify files based on their content and not their names. Of particular note is File Investigator for DOS, Windows and NT.
You can also try out FilExt.com. It’s easy to use.
As for the files you asked about they are as follows:
PAB: Personal Address Book” usually for Outlook or a Microsoft Windows e-mail program.
PST: Personal Folder File. This contains the e-mail messages in Microsoft Outlook.
CFG: This is a configuration file and contains text that is data used by a program.
DFL: Default program settings. This is a file that contains original settings. It may also be a file that contains e-mail signature text.
FCO: I’m not sure what this is used for. The only reference I could find to it said it was a “link”. Whatever it is, it’s not common.
If that proved useful, hopefully so will the following overview of common file extensions. Each includes a quick guide to whether you can delete them.
EXE: These files are the executable part of a program. They contain the code that makes a program run. Sometimes, an entire program exists in an EXE file. Other times, an EXE file needs supporting files to run properly. They can be deleted only if you do not need to run the program ever again. It’s preferable that you use the Install/Uninstall applet in the Windows Control Panel to delete programs.
TXT: These are text files. They simply contain documentation and can be opened with any word processor. They can be deleted if the document is no longer needed.
DOC: These are Microsoft Word files that contain both text and document formatting commands. These can also be deleted at the user’s discretion.
BAT: These files are DOS batch files. They are little programs themselves that run a list of commands. A common BAT file is AUTOEXEC.BAT. It is executed when a computer is started up. It’s not recommended that you delete BAT files unless you know what they are used for. Old versions of BAT files are named with BAK extension and can be safely deleted.
SYS: These are text files as well, but contain system commands. CONFIG.SYS is a common SYS file that implements settings when a computer is started up.
INI: These are initialization files that contain start up information for Windows 95 or older Windows programs. They will be likely phased out in future versions of Windows. They should not be deleted.
ZIP: This is known as a zip file and is a group of files that have been packed together like a bunch of shirts in a suitcase. It is used to archive files and to make files smaller so that they can be transported faster or use less space on a disk. ZIP files can be removed if the files in them have been extracted or are no longer needed.
TMP: These are temporary files used by Windows. They’re like a scratch pad used by Windows to build other files. They usually reside in a directory called C:WINDOWSTEMP, but they do occasionally show up in other directories. These can be deleted, if they are not in use. If Windows is using them, a user won’t be allowed to delete them until Windows is finished with them.
DLL: This is a dynamic link library extension. It’s a toolbox of data. Often, several programs will share a DLL because they contain common instructions that allow repetitive tasks such as creating windows in Windows. Keep these around, unless they seem to be orphaned. Be careful when deleting them as they may be used by a variety of programs.
OCX: This is a Microsoft Object Linking and Embedding custom control. OCX files are small self contained programs that perform a variety of functions that can be used on their own or by other programs. Microsoft recently renamed them as ActiveX controls. These are finicky to delete. They may just be controls that have come from a Web page or them may control your Windows scroll bars. Delete with extreme caution.
HTM and HTML: This is a text file that contains the code that displays a Web page. These can usually be safely deleted.
GIF, JPG, TIF, BMP, PCX: These are all picture files of various types. They can usually be safely deleted, but if they display images in a program, errors may occur. Window stores wallpaper images as BMP files.
MOV, AVI, MPG: These are movie files. Sometimes, they contain just sound, just images or both. They are usually safe to delete.
MP3, WMA, ACC: These are sound files usually containing music.
8BI: This extension indicates a PhotoDeluxe plug-in.
EM: Couldn’t find anything on this one!
When I’m uncertain about removing a file, I rename the file with the word DELETE in its name. For example, a file like ANDY.DLL would be renamed to ANDY.DLL-DELETE. Then I go about my regular computing business and if no errors occur, I delete the file a few weeks later. If there’s a problem, I name the file back to its original name.