Definition: files vs. folders

A file is the common storage unit in a computer, and all programs and data are "written" into a file and "read" from a file. A folder holds one or more files, and a folder can be empty until it is filled. A folder can also contain other folders, and there can be many levels of folders within folders. Folders within a folder are technically known as "subfolders," but this distinction is often disregarded.

Folders provide a method for organizing files much like a manila file folder contains paper documents in a file cabinet. In fact, files that contain text are often called documents.

Folders are also called "directories," and they are created on the hard drive (HD) or solid state drive (SSD) when the operating system and applications are installed. Files are always stored in folders. In fact, even the computer's desktop is a special kind of folder that displays its contents across the screen (see desktop).

File Extensions
Files are identified by a short "extension" following a period at the end of their name. For example, ABC.JPG is a JPEG image, ABC.DOC is a Microsoft Word document file, and ABC.EXE is an executable application in Windows. Although extensions can be added to folder names, extensions are primarily a file convention.

Sometimes Files Are Really Folders
Although not identified as such, what appears to be a single file may really be a folder. For example, starting with Microsoft Word 2007, the default document format was no longer a DOC file, but a DOCX file; in reality, a ZIP archive containing many folders and files (see Office Open XML and ZIP file). The same change occurred in Microsoft Excel 2007, migrating from the XLS to XLSX worksheet formats.

In the Mac, an application has an APP extension, and what appears to be a single file is actually a folder (see APP file). See file, folder and extension.

A Folder Hierarchy

In this Windows example, Program Files is a folder, and Adobe is one of the many subfolders within Program Files. Acrobat Reader DC is a subfolder within Adobe and so on. The Esl and ENU subfolders do not have subfolders, which is why there are no down-pointing arrows associated with them.