What are File-Types?

File Formats Explained in Simple Terms

Computers (and the people who program them) try to be very efficient. So when dealing with the myriad types of data that are needed to be stored, they find different ways to store different data.

Photo Files need a lot of information about exact colours, and the exact location of each pixel. “Writing” documents (such as you might make in Word) record which letters are Capitals, and where the paragraphs are. Spreadsheets have mathematical calculations (often just adding a list of numbers!).

So, the different types of Files are stored in particular Formats (or “types”).

You have probably come across files such as Letter.doc, MyPhoto.jpg, MailAttachment.pdf etc.

The bit after the dot (doc, jpg etc) is called the “File Extension”, and signifies what type of File it is (or more correctly, what Format the file uses to store its data).

So what do they do?

If you are selling your house, you may write a description of it, for the Estate Agent. And they’ll want a photo. You may keep a spreadsheet of the finances involved. You could easily end up with a list of files like this:

  • house.doc
  • house.jpg
  • house.xls
  • house.pdf

Which one is which? Well, from our Summary article, we can look up some of the more common File Formats.

Also, Windows will have a program associated with each File Format, and in File Explorer, each file will be displayed with an Icon of that program.

Different File Format Icons
Different File Format Icons

Note: Windows File Explorer will often show Picture Files as Previews of that picture, as we can see here.

We can easily see that each File has a different Format, by its Icon. That Icon will match the Icon of the associated program.

Icons of some Programs
Icons of some Programs

When you open a File, Windows will check what Format it is, and find the associated program to use. e.g. my system has .doc files associated with “Libre Office Writer” (notice the similar blue icons). You may have “Microsoft Office Word”. The program will open, and display the file.

The programs, such as Word, do not store your files! They can Save your files into the Windows File System (“Documents Folder”, etc), but you do not have Files “in Word”. You have “Word Files” in “Folders”.


File Formats are used by the computer to store data in an efficient manner, and for both you and the computer to tell what “type” a file is.

They determine what program will be used to Open the File (along with its associated Icon).

There are many, many Formats. Some are quite common (.doc, .jpg, .mp3), while others specific to particular Programs (e.g.   .skp Files for storing 3-dimensional information in SketchUp 3D Designer).

Have you seen any rare file types? Do you use custom software with its own special Formats? How do your Icons differ from those presented in this article?

Let me know!

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