What Will the Extension Do?

About this interactive

A file extension is the letters after the last dot in a file's name: the txt in test.txt, the docx in report.docx. Windows uses it to decide what kind of file this is, which icon to show, and which app to open it with when you double-click. Windows hides known extensions by default, so test.txt shows as test. Turn on Show file extensions and the full name appears. That matters when two files share a name, or when you need to know what a file really is. Delete the extension and Windows warns that the file might become unusable. Go ahead and the file loses its icon, and a double-click asks you which app to use, because nothing is linked to a file with no extension. Put the extension back and everything returns. Extensions are often three letters (.txt, .doc, .pdf) but can be four (.docx) or more. The extension is only a label: renaming photo.jpg to photo.txt makes Windows open it in Notepad, but the picture inside is unchanged, so Notepad shows jumbled characters. That is why Windows warns you before you change one. Which app opens a type is the file association, and you can change it. Right-click, Open with, Choose another app: pick an app and choose Just once to use it this time only, or Always to make it the default for every file with that extension (the icons change to match). To change a default later, use Settings, Default apps, which lists the extensions and the app linked to each.

What you'll learn

Predict what Windows does with a file from its extension: which app opens it, and what happens when the extension is hidden, removed, changed or put back
Set the app that opens a file type, once or always, from Open with or from Settings, Default apps

Aligned to

CompTIA Tech+

3.2 Compare and contrast components of an operating system.

1.2 Compare and contrast fundamental data types and their characteristics.

Key terms

File Extension: A suffix appended to a filename after a period that identifies the file format and tells the operating system which program to use to open it.
File Association: The link between a file extension and the application the operating system uses to open files of that type.
Default Application: The program an operating system automatically uses to open a specific file type based on its extension.
File: A named collection of data stored on a storage medium and tracked by the file system, which records its name, location, size, and attributes so the operating system can retrieve it on demand.

Topics

File Extension File Association Default Application Interactive Predict

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