File Types - Basic Classes

In this lesson you will learn:

This section describes techniques for determining which program will open the file. We'll look at types of files as well as the file extensions on a typical PC.

Types of Files

Each file on the computer has a specific program that opens that TYPE of file. For instance, pictures, spreadsheets, databases, word processing and music files are all opened with different types of programs. Trying to open a music file with a word processing file will open a box which will ask which file you want to try to use to open it. The box is letting you know that the program cannot open that file type. So it is very helpful to know which program opens which file, and that is determined by the file extension.

So how do you know, and how does the computer know which program to use? It knows because of the 'file type' the file was saved in. Each file name has three parts:

Even in you can't actually see the dot and the last characters they are always there. The ability to see the extension depends of a few things:

File name extensions look like this: .txt or .doc, or .xls, or .pdf. In order to see these, if you can't already, may require a few changes in Windows Explorer:

NOTE: If you cannot see the file extensions at this point ask your computer instructor. DO NOT try to continue without changing the settings to see these extensions!

The extension generally has three or four characters following a dot. These characters determine which type of program created the file, and thus, which type of program will open the file again. The extensions are necessary because without them there is no way of knowing which program the file belongs to. This is called 'association' and the term is 'File Association'. File Association can be changed so that another program will open it instead of the current program that opens it. This is useful for pictures and media (audio and video) so that you can select the program that you want to open it, not what the computer 'decided'.

When a file is saved there are two boxes at the bottom of the window: One box is for the file name that you give it, like 'My Grocery List'. The box below it has a drop-down arrow and pressing this shows that there are several possibilities to choose from. Changing the selection in this box is changing the file formatting so that that program will open it, and it changes the file association.

In other words each one of the items in the drop down list is telling the computer to open your file with a different program. It is important to understand what some of the basic file types are, because pointing the file to open with the wrong program will change it. For example, .txt means that the file will open in a text editor, which means only text will show; no margins, no fonts, no colors, no headers or footers or any other formatting. So the nice file you made is stripped down to bare text. Choosing a Word processor program (like Microsoft Word or Works) will show all of the formatting.

File extensions are something you generally do not need to be concerned about. If you open a new file and save it in the same program, the extension does not change. In order for the extension to change you have to change it. There are very few reasons for beginning computer users to ever need to change a file extension. For this reason the Operating System, like Windows or Unix, generally hide the file extensions so that they are not visible when browsing folders and files. In the case that you are at a computer that shows dot three extensions, now you know what they are and what they are for.

Data Files that Open up Programs

As outlined above, double clicking the data file you want to open will open the file in the program that created it. Different types of programs open different types of files. The type of program that will create or open the file is identified by the file extension, the letters after the dot in the file name. This was sometimes called dot 3 notation because most file extensions were limited to 3 characters after the dot. That is no longer the case so they can be longer or shorter.

File Extensions

By examining the file name extension, you can tell basically what type of file it is. A file with a .gif extension is an image file, as is .bmp or .jpg . Files with the extension of .doc, .rtf, or .txt are document files. Files with the extension of .ram, .mov or .avi are movie files. You do not have to memorize the file extensions. All you have to do is double click the file. The document, picture, sound file or movie loads in the workspace of the program that created it. For instance, if the program is a document, double clicking it will open the program in the word processing program that created it.

Here is a partial list of file extensions and the programs that will open when double clicking on the file. This is only a very brief list, as an extensive list is actually an entire book of 200 + pages.

File Associations

There are a lot of files that open automagically using a program on one computer and an entirely different program on another computer. For instance, clicking on a sound file can open up Windows Media Player, Real Audio, or Quick Viewer, depending on the File Associations. If the program opens in a wrong file type, then opening up the program that you want and going to 'Preferences' or 'Settings' will allow you to select that file type from a list. It also allows you to choose whether to allow this program to be the 'Default' program. If you make the program the default, then it will open that file type instead of the other program.

File Associations are important when it comes to naming, or especially re-naming files. If you try to name a file and do not use a file extension, you may or may not get an error warning you that there is no program on your computer that will open that file! Worse yet, you may inadvertently miss-type the extension, and it will either open with a different program entirely, or there will be a dialog box prompting you to point to the program you want to open it in.

If you know that the file is supposed to be opened by a word processor, such as MS Word or Word Perfect or another Word Processor, just select that program from the list, and at the bottom, place a check mark in 'Always use this program to open the files of type' check box. Then, as mentioned above, double clicking the file will use the program you chose to always open the file. You have 'associated' the new extension with a program to open it.

Changing File extensions is used by technicians and repair personnel and is not for the faint hearted or to be taken lightly. In the worse case, you will have to re-create the file. In some cases, manual re-associations are a nightmare of re-listing every file type. If you try to re-name a system file, you will get an error. If you don't and are able to re-associate a system file type, your computer could fail to restart, which is quite a repair bill. Re-naming the file again using a program outside of windows is outside the scope of this lesson, but you get the idea.... not good. Re-naming the file may not 'fix' it again if the file was changed to the new program format! Major repair.

These techniques are also useful for 'corrupt' files. If the original program will not open it without errors, try changing the file extension so that another similar program will attempt to open it.

If you name the file properly in the first place, these associations will be transparent and you will never have to be concerned about them. If a mistake is made, all is not lost, and you can easily change the extension until something opens that will read the file. Then, after you know basically what kind of file it is, whether Database, Text, Media, etc, then you can re-name the extension so the proper program opens it.

But how do you know which programs open which extensions? That is a more advanced topic covered in another lesson. These are usually default settings based on choices made by the user or programmatically when the program is first created or installed. Installing Software is a big subject, and is covered in higher beginning and intermediate courses.