File Extension Reference

A file extension is a suffix at the end of a filename that indicates its format and content type to the operating system and user. It is separated from the main filename by a period (e.g., document.pdf). Knowing file extensions helps you understand how to open a file, which program to use for editing, and whether the file is potentially dangerous. This reference covers the most common file extensions encountered by every computer user.

System Files and Executable Files

Files required for the operating system and programs to function.

.exe (Executable)

Purpose: An executable program file in Windows.

Description: Launches the installation or execution of an application. Should only be opened from trusted sources, as viruses often disguise themselves as .exe files.

.msi (Microsoft Installer)

Purpose: An installer file for Windows programs.

Description: Contains information for installing, updating, or uninstalling a program. More standardized than the .exe installer.

.dll (Dynamic Link Library)

Purpose: Dynamic link library.

Description: Contains code and data that can be used by multiple programs simultaneously. Not intended to be run directly by the user.

.sys (System File)

Purpose: System device driver file in Windows.

Description: Enables interaction between the operating system and hardware components (video card, printer, etc.).

.ini (Initialization File)

Purpose: Program configuration file.

Description: Stores program settings in plain text format. Can be opened and edited in Notepad.

.tmp (Temporary File)

Purpose: Temporary file.

Description: Created by programs to store intermediate data. Typically deleted automatically after closing the program.

Text Documents and Office Files

Files for working with text, tables, and presentations.

.txt (Plain Text)

Purpose: A plain text file.

Description: Contains only text without formatting (bold, italics, etc.). Can be opened with any text editor (Notepad, Notepad++).

.doc / .docx (Microsoft Word Document)

Purpose: A text document with formatting.

Description: .doc is the old Word format, .docx is a modern XML-based format. Contains text, images, and tables with complex formatting.

.pdf (Portable Document Format)

Purpose: A portable document format.

Description: Maintains the document"s precise formatting regardless of the device. Ideal for printing and distributing documents that are not intended for editing.

.xls / .xlsx (Microsoft Excel Spreadsheet)

Purpose: Spreadsheet file.

Description: Contains data organized into rows and columns, formulas, graphs, and charts. .xlsx is a modern version of the format.

.ppt / .pptx (Microsoft PowerPoint Presentation)

Purpose: Presentation file.

Description: Contains slides with text, images, animation, and multimedia for presentations.

.odt (OpenDocument Text)

Purpose: Open text document format.

Description: Similar to .docx for free office suites (LibreOffice, OpenOffice). Standard for government agencies in many countries.

Images and Graphic Files

Files for storing photographs, images, and vector graphics.

.jpg / .jpeg (Joint Photographic Experts Group)

Purpose: Photographs and images with smooth transitions.

Description: The most popular format for photographs. Uses lossy compression. Does not support transparency.

.png (Portable Network Graphics)

Purpose: Images with transparency and sharp edges.

Description: Uses lossless compression. Supports transparent backgrounds. Ideal for screenshots, logos, and web graphics.

.gif (Graphics Interchange Format)

Purpose: Simple animations and images with a limited palette.

Description: Supports animation and simple transparency. Limited to 256 colors.

.bmp (Bitmap Image)

Purpose: Uncompressed raster image.

Description: Stores the color data of each pixel without compression. Provides high quality, but has a very large file size.

.svg (Scalable Vector Graphics)

Purpose: Vector image.

Description: Describes an image using mathematical shapes and lines. Scalable without loss of quality. Used for icons, logos, and graphs.

.ico (Icon File)

Purpose: Icon file.

Description: Contains one or more icons of varying sizes to represent files, folders, and programs in the operating system.

.psd (Photoshop Document)

Purpose: Adobe Photoshop project.

Description: Preserves all layers, effects, and image settings. Can only be opened in Photoshop and some other graphic editors.

Audio and Video Files

Files for storing music, audio recordings, and video.

.mp3 (MPEG-1 Audio Layer 3)

Purpose: Compressed audio file.

Description: The most popular format for storing music. Provides a good balance between quality and file size.

.wav (Waveform Audio File Format)

Purpose: Uncompressed audio file.

Description: Preserves audio in its original quality. Used in professional audio recording. Has a large file size.

.mp4 (MPEG-4 Part 14)

Purpose: General-purpose video file.

Description: A container that can contain video, audio, and subtitles. A standard for online videos and movies.

.avi (Audio Video Interleave)

Purpose: Video file (obsolete, but widespread).

Description: One of the first popular video formats. Files are typically larger than .mp4 files of the same quality.

.mkv (Matroska Video)

Purpose: Flexible video container.

Description: Supports multiple video and audio tracks, complex subtitles. Popular for storing movies.

Archives and Compressed Files

Files containing one or more other files in compressed form.

.zip (ZIP Archive)

Purpose: Compressed archive.

Description: The most popular archive format. Supported on all operating systems without additional software.

.rar (Roshal ARchive)

Purpose: Highly compressed archive.

Description: Provides better compression than ZIP. Supports multi-volume archives (parts of .rar, .r00, .r01, etc.).

.7z (7-Zip Archive)

Purpose: Archive with maximum compression.

Description: Open source format. Often provides the best compression ratio among popular archivers.

.tar.gz / .tgz (Tarball Archive)

Purpose: Archive on Unix systems.

Description: .tar concatenates files, .gz compresses them. The standard format for software distribution on Linux.

Web Files and Scripts

Files used to create websites and automate tasks.

.html / .htm (HyperText Markup Language)

Purpose: Web page.

Description: Contains the markup and content of a web page. Opens in a browser.

.css (Cascading Style Sheets)

Purpose: Style sheets for web pages.

Description: Defines the appearance of an HTML document (fonts, colors, element layout).

.js (JavaScript File)

Purpose: Script for web pages.

Description: Adds interactivity and dynamic behavior to websites.

.php (PHP: Hypertext Preprocessor)

Purpose: Server-side script.

Description: Code that is executed on the web server before sending a page to the user.

.py (Python Script)

Purpose: A Python script.

Description: A text program executed by the Python interpreter.

.bat (Batch File)

Purpose: A Windows batch file.

Description: Contains a sequence of commands for the Windows command line (CMD). Used to automate tasks.

.iso (ISO Image)

Purpose: An optical disc image.

Description: An exact copy of a CD, DVD, or Blu-ray disc. Can be mounted as a virtual drive or burned to physical media.