Table of Contents
Today we will share SSC Computer Class File Extension PPT Slides (LEC #25) so, File extensions are one of the easiest and most rewarding topics in the SSC Computer Awareness syllabus. A single question asking which extension belongs to which file type – or which software opens a particular format – can be the difference between clearing a cutoff or missing it. Questions on file extensions appear consistently across SSC CGL, SSC CHSL, SSC MTS, RRB NTPC, and RRB Group D exams. This article is based on the LEC #25 PPT slides from the Complete Foundation Batch and covers every category of file extension you need – documents, images, audio, video, compressed files, executables, web files, code files, and more – along with MIME types, security concerns, exam-important facts, FAQs, and practice MCQs.
Lecture Details
| Parameter | Details |
| Lecture Number | LEC #25 |
| Topic | File Extension |
| Subject | Computer Awareness – SSC Foundation Batch |
| Total Slides | 20 |
| File Size | 3 MB |
| Exam Relevance | SSC CGL, SSC CHSL, SSC MTS, SSC CPO, RRB NTPC, RRB Group D, UPSSSC PET |
SSC Computer Class File Extension PPT Slides (LEC #25)
NOTE: IF YOU WANT TO DOWNLOAD COMPLETE SSC SERIES (PPT SLIDES) – JUST VISIT THIS REDIRECT PAGE
What Is a File Extension?
A file extension (also called a filename extension or file suffix) is a set of characters added at the end of a filename, separated by a period (dot), that indicates the type and format of the file. The operating system uses the file extension to determine which program should open the file.
For example, in the filename Report.docx – ‘Report’ is the filename and ‘.docx’ is the file extension. The extension tells the OS this is a Microsoft Word document, so it should open with Microsoft Word.
| Component | Definition | Example |
| Filename | The name given to the file by the user or the system | Report, Photo, Budget, Song |
| Dot / Period (.) | The separator between the filename and the extension | The dot in Report.docx |
| File Extension | Characters after the dot that indicate file type and format | .docx, .jpg, .mp3, .exe, .pdf |
| Full Filename | Complete name including both filename and extension | Report.docx, Photo.jpg, Song.mp3 |
| Hidden Extensions | Some OS (especially Windows) hides known extensions by default – a setting that can be changed | photo.jpg shown as ‘photo’ in Windows Explorer |
| Case Sensitivity | On Linux/Unix, extensions are case-sensitive (.JPG and .jpg are different); on Windows they are not | .MP3 and .mp3 are the same on Windows, different on Linux |
Why File Extensions Matter
| Purpose | Description |
| File Type Identification | Tells the operating system and user what kind of data is stored in the file |
| Default Application Mapping | The OS uses the extension to decide which application opens the file automatically on double-click |
| File Association | Users can change which application is associated with a particular extension in OS settings |
| Security Screening | Antivirus software and email servers scan extensions to detect potentially dangerous files (e.g., .exe, .bat, .vbs attached in emails) |
| File Format Compatibility | Ensures a file is opened with compatible software – a .psd file needs Photoshop; a .docx needs Word or a compatible editor |
| Web Server Handling | Web servers use extensions to determine MIME types and serve files correctly to browsers |
File Extensions by Category
Document and Text File Extensions
| Extension | File Type | Associated Software | Notes |
| .doc | Microsoft Word Document (older format) | Microsoft Word | Binary format; used in Word 97–2003; largely replaced by .docx |
| .docx | Microsoft Word Document (modern format) | Microsoft Word, LibreOffice Writer, Google Docs | XML-based format introduced in Office 2007; default Word format today |
| Portable Document Format | Adobe Acrobat Reader, Foxit, browsers | Created by Adobe; preserves formatting across all devices; not easily editable | |
| .txt | Plain Text File | Notepad, any text editor | No formatting; smallest size; compatible with every OS and application |
| .rtf | Rich Text Format | Microsoft Word, WordPad, LibreOffice | Supports basic formatting; cross-platform; larger than .txt |
| .odt | OpenDocument Text | LibreOffice Writer, Google Docs | Open standard; default format of LibreOffice Writer |
| .xls | Microsoft Excel Spreadsheet (older format) | Microsoft Excel | Binary format; used in Excel 97–2003 |
| .xlsx | Microsoft Excel Spreadsheet (modern format) | Microsoft Excel, LibreOffice Calc, Google Sheets | XML-based; default Excel format since Office 2007 |
| .ods | OpenDocument Spreadsheet | LibreOffice Calc, Google Sheets | Open standard spreadsheet format |
| .ppt | Microsoft PowerPoint Presentation (older) | Microsoft PowerPoint | Binary format; used in PowerPoint 97–2003 |
| .pptx | Microsoft PowerPoint Presentation (modern) | Microsoft PowerPoint, LibreOffice Impress, Google Slides | XML-based; default PowerPoint format since Office 2007 |
| .odp | OpenDocument Presentation | LibreOffice Impress | Open standard presentation format |
| .csv | Comma-Separated Values | Microsoft Excel, LibreOffice Calc, any text editor | Plain text; each value separated by a comma; used for data exchange between systems |
| .xml | eXtensible Markup Language | Browsers, text editors, any XML parser | Self-describing data format; used for data storage and exchange |
| .json | JavaScript Object Notation | Text editors, web browsers, development tools | Lightweight data exchange format; widely used in web APIs |
| .html / .htm | HyperText Markup Language | Web browsers (Chrome, Firefox, Edge) | Standard format for web pages; .htm is an older 3-character version of .html |
Image and Graphics File Extensions
| Extension | Full Name | Type | Key Feature |
| .jpg / .jpeg | Joint Photographic Experts Group | Lossy compressed raster | Most common image format for photos; smaller file size; slight quality loss on compression |
| .png | Portable Network Graphics | Lossless compressed raster | Supports transparency (alpha channel); better quality than JPG for graphics; larger file size |
| .gif | Graphics Interchange Format | Lossless, limited palette raster | Supports simple animations; limited to 256 colors; used for animated images on web |
| .bmp | Bitmap Image File | Uncompressed raster | Created by Microsoft; no compression; very large file size; high quality |
| .tiff / .tif | Tagged Image File Format | Lossless raster | Professional printing and scanning; very high quality; very large files |
| .svg | Scalable Vector Graphics | Vector | XML-based; scales to any size without losing quality; used for logos and icons on web |
| .webp | Web Picture format | Lossy/lossless raster | Developed by Google; 25–35% smaller than JPG/PNG; modern web standard |
| .raw | Raw Image File | Unprocessed raster | Unprocessed data directly from camera sensor; used by professional photographers |
| .psd | Photoshop Document | Layered raster | Adobe Photoshop’s native format; stores layers, masks, and effects |
| .ico | Icon File | Raster | Used for application and website icons (favicon); contains multiple image sizes |
| .heic / .heif | High Efficiency Image Format | Lossy compressed raster | Default photo format on iPhones (iOS 11+); half the size of JPG at same quality |
Audio File Extensions
| Extension | Full Name | Compression | Key Feature |
| .mp3 | MPEG Audio Layer 3 | Lossy | Most popular audio format worldwide; good quality at small file size; universally supported |
| .wav | Waveform Audio File Format | Uncompressed | Developed by Microsoft and IBM; CD-quality audio; very large files; used in professional audio editing |
| .aac | Advanced Audio Coding | Lossy | Successor to MP3; better quality at same bitrate; default format for Apple iTunes and iOS |
| .flac | Free Lossless Audio Codec | Lossless | No quality loss; about half the size of WAV; preferred by audiophiles for archiving music |
| .ogg | Ogg Vorbis | Lossy | Open-source format; free to use; used in games and streaming platforms |
| .wma | Windows Media Audio | Lossy | Microsoft’s proprietary audio format; used in Windows Media Player |
| .m4a | MPEG-4 Audio | Lossy (AAC) | Audio-only version of MP4; used by Apple for iTunes purchases |
| .mid / .midi | Musical Instrument Digital Interface | None (data, not audio) | Stores musical notes and instructions, not actual audio; very small files; used in electronic music |
| .aiff / .aif | Audio Interchange File Format | Uncompressed | Apple’s uncompressed audio format; equivalent to WAV; used on macOS |
Video File Extensions
| Extension | Full Name | Developer | Key Feature |
| .mp4 | MPEG-4 Part 14 | Moving Picture Experts Group (MPEG) | Most widely used video format today; good quality at small size; supported on all devices and platforms |
| .avi | Audio Video Interleave | Microsoft (1992) | Older Microsoft format; large file size; high quality; widely supported on Windows |
| .mkv | Matroska Video | Open Standard (Matroska) | Open-source container; supports multiple audio tracks, subtitles, and chapters in one file |
| .mov | QuickTime Movie | Apple Inc. | Apple’s video format; high quality; used on macOS and iOS; compatible with QuickTime Player |
| .wmv | Windows Media Video | Microsoft Corporation | Microsoft’s video format; optimized for Windows Media Player; used for streaming on Windows |
| .flv | Flash Video | Adobe Systems | Formerly used for web video (YouTube’s old format); largely replaced by MP4/WebM |
| .webm | WebM Video | Google (open standard) | Open web video format by Google; used for HTML5 video on websites; smaller than MP4 |
| .3gp | 3rd Generation Partnership Project | 3GPP consortium | Designed for mobile phones; small file size; used on older feature phones and Android |
| .mpeg / .mpg | Moving Picture Experts Group | MPEG consortium | Older standard compression format; used for DVDs and VCDs |
Compressed and Archive File Extensions
Compressed files reduce the size of one or more files for storage or transfer. Archive files bundle multiple files into a single container, with or without compression.
| Extension | Full Name | Developer / Standard | Key Feature |
| .zip | ZIP Archive | Phil Katz / PKWARE (1989) | Most popular archive format worldwide; built into Windows and macOS; fast compression |
| .rar | Roshal Archive | Eugene Roshal (1993) | Better compression ratio than ZIP; requires WinRAR or 7-Zip to extract; supports multi-part archives |
| .7z | 7-Zip Archive | Igor Pavlov / 7-Zip (open source) | Very high compression ratio; open-source; supports strong AES-256 encryption |
| .tar | Tape Archive | Unix standard | Bundles files into one without compression; often combined with gzip (.tar.gz) or bzip2 (.tar.bz2) |
| .gz / .gzip | GNU Zip | GNU Project | Compression tool commonly used on Linux/Unix; applied to .tar files to create .tar.gz |
| .bz2 | Bzip2 Compressed File | Julian Seward (open source) | Better compression than gzip; slower; used on Linux for archiving |
| .iso | ISO Disc Image | ISO 9660 standard | Exact byte-for-byte copy of a CD/DVD/Blu-ray disc; used to distribute OS installers |
| .cab | Cabinet File | Microsoft Corporation | Windows compressed archive used for software installers and Windows updates |
Executable and System File Extensions
Executable files contain code or instructions that the operating system can run directly. These are critical from a security perspective – malware often hides in executable file formats.
| Extension | File Type | Platform | Security Risk |
| .exe | Executable File | Windows | HIGH – can run programs; commonly used to distribute both legitimate software and malware |
| .msi | Microsoft Installer Package | Windows | Medium – installs software on Windows; can contain malicious payloads |
| .bat | Batch Script File | Windows | Medium-High – runs a sequence of Windows commands automatically; used in automation and attacks |
| .cmd | Command Script | Windows | Medium-High – similar to .bat; Windows command script; can execute system commands |
| .sh | Shell Script | Linux / macOS (Unix) | Medium – executes shell commands on Linux/Unix; requires execution permission |
| .apk | Android Package Kit | Android | Medium – Android app installer; sideloaded APKs from unknown sources can be dangerous |
| .ipa | iOS App Archive | iOS / macOS | Low (from App Store) – iOS application installer; tightly controlled by Apple |
| .dll | Dynamic Link Library | Windows | Medium – shared library loaded by .exe programs; malware sometimes replaces legitimate DLLs |
| .sys | System File | Windows | High (if modified) – Windows device driver or kernel file; critical for OS operation |
| .bin | Binary Executable / Raw Binary | Linux / Universal | Varies – generic binary file; could be a program, firmware, or disc image |
| .vbs | VBScript File | Windows | HIGH – Visual Basic Script; frequently used in email phishing attacks and malware |
| .ps1 | PowerShell Script | Windows | HIGH – PowerShell script; increasingly used in advanced malware attacks |
Web Development File Extensions
| Extension | Full Name | Language / Technology | Role in Web Development |
| .html / .htm | HyperText Markup Language | HTML | Structure of a web page – headings, paragraphs, links, images, tables |
| .css | Cascading Style Sheets | CSS | Styling – controls colors, fonts, layout, spacing, and visual design of web pages |
| .js | JavaScript File | JavaScript | Interactivity and dynamic behavior of web pages – animations, form validation, API calls |
| .ts | TypeScript File | TypeScript (Microsoft) | Typed superset of JavaScript; compiled to JS before running in browsers |
| .php | PHP: Hypertext Preprocessor | PHP | Server-side scripting – generates dynamic HTML; powers WordPress, Facebook (early) |
| .asp / .aspx | Active Server Pages | Microsoft ASP.NET | Server-side web pages built with Microsoft’s ASP.NET framework |
| .jsp | JavaServer Pages | Java | Server-side Java web pages; generates dynamic HTML using Java code embedded in HTML |
| .xml | eXtensible Markup Language | XML | Data storage and exchange; used in RSS feeds, configuration files, web APIs |
| .json | JavaScript Object Notation | Language-independent | Lightweight data format for web API responses; easy to parse in any programming language |
| .svg | Scalable Vector Graphics | XML-based | Vector graphics format for web; logos and icons that scale without quality loss |
Programming and Source Code File Extensions
| Extension | Language | Key Use |
| .c | C Language | System programming, operating systems, embedded systems |
| .cpp / .cxx | C++ Language | Game development, system software, OOP applications |
| .h | C / C++ Header File | Declarations and definitions shared across multiple C/C++ source files |
| .java | Java Language | Enterprise applications, Android development, web back-end |
| .class | Java Compiled Bytecode | Compiled Java program; run by the Java Virtual Machine (JVM) |
| .jar | Java Archive | Packaged Java application or library; similar to ZIP but for Java |
| .py | Python Language | Data science, AI/ML, web development, automation, scripting |
| .pyc | Python Compiled Bytecode | Compiled Python cache file; generated automatically by Python interpreter |
| .js | JavaScript | Web front-end interactivity; also server-side with Node.js |
| .ts | TypeScript | Typed JavaScript superset; used in large-scale web applications |
| .cs | C# (C-Sharp) | Windows applications, game development (Unity), .NET ecosystem |
| .rb | Ruby Language | Web development (Ruby on Rails), scripting |
| .php | PHP Language | Server-side web development; WordPress, Drupal, Joomla |
| .swift | Swift Language (Apple) | iOS and macOS app development |
| .kt | Kotlin Language | Android app development; JVM-based language |
| .go | Go (Golang) Language | Cloud services, back-end development, CLI tools (Google) |
| .r | R Language | Statistical computing, data analysis, data visualization |
| .sql | SQL Script File | Database queries and schema definitions |
| .sh | Shell Script | Linux/macOS command-line automation |
| .bat | Windows Batch Script | Windows command-line automation |
Database and Data File Extensions
| Extension | File Type | Associated Software |
| .db | Generic Database File | SQLite, various database applications |
| .sqlite / .sqlite3 | SQLite Database | SQLite – lightweight embedded database used in mobile apps |
| .sql | SQL Script / Dump File | MySQL, PostgreSQL, SQL Server – used to export/import database schemas and data |
| .mdb | Microsoft Access Database (old) | Microsoft Access 97–2003 |
| .accdb | Microsoft Access Database (modern) | Microsoft Access 2007 and later |
| .csv | Comma-Separated Values | Excel, LibreOffice Calc, any database import tool |
| .json | JSON Data File | MongoDB, web APIs, NoSQL databases |
| .xml | XML Data File | Any XML-compatible database or parser |
| .bak | Database Backup File | SQL Server, MySQL, PostgreSQL – backup and restore operations |
Font File Extensions
| Extension | Full Name | Key Feature |
| .ttf | TrueType Font | Developed by Apple and Microsoft in the 1980s; widely used on Windows and macOS; scalable |
| .otf | OpenType Font | Developed by Adobe and Microsoft; supports more advanced typographic features than TTF |
| .woff | Web Open Font Format | Optimized for web use; compressed TTF/OTF; supported by all modern browsers |
| .woff2 | Web Open Font Format 2 | Next generation WOFF; 30% better compression; recommended for modern web fonts |
| .eot | Embedded OpenType | Microsoft’s proprietary web font format; used only in older Internet Explorer versions |
Microsoft Office vs LibreOffice vs Google Workspace – Extension Comparison
| Document Type | Microsoft Office | LibreOffice (Open Format) | Google Workspace (Cloud) |
| Word Processor | .docx (.doc old) | .odt (OpenDocument Text) | .gdoc (Google Docs – cloud-only) |
| Spreadsheet | .xlsx (.xls old) | .ods (OpenDocument Spreadsheet) | .gsheet (Google Sheets – cloud-only) |
| Presentation | .pptx (.ppt old) | .odp (OpenDocument Presentation) | .gslides (Google Slides – cloud-only) |
| Database | .accdb (.mdb old) | .odb (OpenDocument Database) | Google Sheets used as lightweight DB |
| Drawing / Vector | .vsdx (Visio) | .odg (OpenDocument Drawing) | Google Drawings (.gdraw) |
Exam tip: The ‘x’ in .docx, .xlsx, and .pptx stands for XML – these formats are based on Open XML. They were introduced with Microsoft Office 2007 (also called Office 12).
Lossy vs Lossless Compression in Image Formats
| Parameter | Lossy Compression | Lossless Compression |
| Definition | Some image data is permanently discarded during compression to achieve smaller file sizes | The original image data is perfectly preserved; file can be fully reconstructed |
| File Size | Smaller – significant size reduction | Larger than lossy, smaller than uncompressed |
| Quality | Some quality loss visible at high compression levels | No quality loss – pixel-perfect reproduction |
| Best For | Photographs, social media images, web use where some quality loss is acceptable | Graphics, logos, screenshots, medical images, archiving |
| Formats | .jpg, .webp (lossy mode), .heic | .png, .gif, .bmp, .tiff, .webp (lossless mode), .flac (audio) |
| Editing | Quality degrades further with each save (generation loss) | No degradation on repeated saves |
MIME Types – What They Are and Why They Matter
MIME stands for Multipurpose Internet Mail Extensions. A MIME type (also called a media type or content type) is a standardized label that identifies the format and nature of a file transmitted over the internet. Web servers include the MIME type in HTTP response headers so browsers know how to handle the received file.
| Extension | MIME Type | What the Browser Does |
| .html | text/html | Renders as a web page |
| .css | text/css | Applies as a stylesheet |
| .js | application/javascript | Executes as a script |
| .json | application/json | Parses as JSON data |
| .xml | application/xml or text/xml | Parses or displays as XML |
| .jpg / .jpeg | image/jpeg | Displays as an image |
| .png | image/png | Displays as an image |
| .gif | image/gif | Displays as an animated or static image |
| .svg | image/svg+xml | Renders as a scalable vector image |
| application/pdf | Opens in PDF viewer plugin or prompts download | |
| .mp3 | audio/mpeg | Plays in audio player |
| .mp4 | video/mp4 | Plays in video player |
| .zip | application/zip | Prompts file download |
| .exe | application/octet-stream | Prompts download; browser does not execute |
File Extensions and Cybersecurity
File extensions play a critical role in cybersecurity. Attackers often exploit file extensions to trick users into running malicious files. This is a tested topic in SSC Computer Awareness.
| Threat | Description | Example |
| Double Extension Attack | Malware named with a fake extension followed by the real dangerous one; Windows may hide the last extension if ‘hide known extensions’ is enabled | photo.jpg.exe – appears as ‘photo.jpg’ but is actually an executable |
| Macro Malware in Office Files | Malicious macros embedded in .doc, .xls, or .docx files that execute on opening if macros are enabled | invoice.docx containing a macro that downloads ransomware |
| Executable Disguised as Media | Malware with an icon that looks like a media file but is actually an .exe or .bat | movie.avi.exe disguised with a video player icon |
| VBScript and PowerShell Attacks | .vbs and .ps1 files that run scripts to compromise the system; often delivered via phishing emails | bill_payment.vbs attached to a phishing email |
| PDF Exploits | Maliciously crafted .pdf files that exploit vulnerabilities in PDF readers to execute code | Specially crafted PDF that exploits an unpatched Adobe Reader bug |
| ZIP Bombs | .zip files that appear small but extract to terabytes of data, crashing systems or consuming all disk space | 42.zip – a 42 KB ZIP that extracts to 4.5 petabytes |
Security best practices: Always show file extensions in your OS (disable ‘hide known file type extensions’ in Windows). Never open .exe, .bat, .vbs, .ps1, or .cmd files from unknown sources. Keep your antivirus and OS updated.
Important File Extension Facts for SSC Exams
| Fact | Details |
| PDF created by | Adobe Systems; PDF stands for Portable Document Format; introduced in 1993 by John Warnock |
| JPEG named after | Joint Photographic Experts Group – the committee that created the standard in 1992 |
| GIF supports animation | GIF (Graphics Interchange Format) is the only widely supported image format that supports frame-based animations in web browsers without plugins |
| PNG developed as | PNG (Portable Network Graphics) was developed as an improved, free alternative to GIF in 1996; supports alpha transparency |
| MP3 developed by | Fraunhofer Society (Germany) with contributions from Karlheinz Brandenburg; standardized by MPEG in 1993 |
| ZIP created by | Phil Katz, who created the PKZIP program in 1989; the format is now maintained by PKWARE |
| The ‘x’ in .docx/.xlsx/.pptx | The ‘x’ stands for XML – these formats are based on the Open XML standard introduced with Microsoft Office 2007 |
| .exe restriction on email | Gmail, Outlook, and most email providers block .exe attachments to prevent malware delivery |
| Favicon extension | Website favicons (the small icon in browser tabs) use the .ico format |
| Default Windows screenshot format | Windows Vista and later save screenshots in PNG format by default (Snipping Tool, Snip & Sketch) |
| RAW in photography | Camera RAW formats (.raw, .cr2, .nef, .arw) store unprocessed sensor data; each camera brand has its own RAW format |
| ISO and disc images | .iso is a bit-for-bit copy of an optical disc; used to distribute Linux OS installers and bootable Windows images |
| FLAC and lossless audio | FLAC (Free Lossless Audio Codec) is the most popular lossless audio format; preferred by audiophiles over MP3 |
| .apk and Android | Every Android app is distributed as an .apk (Android Package Kit) file; installing APKs from unknown sources is a security risk |
| Difference .doc vs .docx | .doc is the older binary Microsoft Word format (Office 97–2003); .docx is the newer XML-based format (Office 2007+); .docx is smaller and more reliable |
Master Quick Reference – Extension to File Type
| Extension | File Type | Category |
| .docx | Microsoft Word Document | Document |
| .xlsx | Microsoft Excel Spreadsheet | Document |
| .pptx | Microsoft PowerPoint Presentation | Document |
| Portable Document Format | Document | |
| .txt | Plain Text File | Document |
| .csv | Comma-Separated Values | Document / Data |
| .jpg / .jpeg | JPEG Image | Image |
| .png | Portable Network Graphics | Image |
| .gif | Graphics Interchange Format (animated) | Image |
| .bmp | Bitmap Image | Image |
| .svg | Scalable Vector Graphics | Image / Web |
| .mp3 | MPEG Audio Layer 3 | Audio |
| .wav | Waveform Audio | Audio |
| .aac | Advanced Audio Coding | Audio |
| .flac | Free Lossless Audio Codec | Audio |
| .mp4 | MPEG-4 Video | Video |
| .avi | Audio Video Interleave | Video |
| .mkv | Matroska Video | Video |
| .mov | QuickTime Movie | Video |
| .zip | ZIP Archive | Compressed |
| .rar | Roshal Archive | Compressed |
| .7z | 7-Zip Archive | Compressed |
| .iso | ISO Disc Image | Compressed / Disc |
| .exe | Windows Executable | Executable |
| .apk | Android Package Kit | Executable |
| .bat | Windows Batch Script | Executable / Script |
| .dll | Dynamic Link Library | System |
| .html | HyperText Markup Language | Web |
| .css | Cascading Style Sheets | Web |
| .js | JavaScript File | Web / Code |
| .py | Python Source Code | Code |
| .java | Java Source Code | Code |
| .c | C Language Source Code | Code |
| .sql | SQL Script / Database Dump | Database / Code |
| .ttf | TrueType Font | Font |
| .woff | Web Open Font Format | Font / Web |
File Extension Abbreviations – Quick Reference
| Abbreviation | Full Form |
| Portable Document Format | |
| JPEG / JPG | Joint Photographic Experts Group |
| PNG | Portable Network Graphics |
| GIF | Graphics Interchange Format |
| BMP | Bitmap |
| SVG | Scalable Vector Graphics |
| TIFF | Tagged Image File Format |
| MP3 | MPEG Audio Layer 3 |
| MPEG | Moving Picture Experts Group |
| WAV | Waveform Audio File Format |
| AAC | Advanced Audio Coding |
| FLAC | Free Lossless Audio Codec |
| AVI | Audio Video Interleave |
| MKV | Matroska Video |
| WMV | Windows Media Video |
| WMA | Windows Media Audio |
| ZIP | Zone Information Protocol (retronym – originally no acronym) |
| RAR | Roshal Archive |
| ISO | International Organization for Standardization (disc image standard) |
| EXE | Executable |
| DLL | Dynamic Link Library |
| APK | Android Package Kit |
| IPA | iOS App Archive |
| HTML | HyperText Markup Language |
| CSS | Cascading Style Sheets |
| JS | JavaScript |
| JSON | JavaScript Object Notation |
| XML | eXtensible Markup Language |
| PHP | PHP: Hypertext Preprocessor |
| MIME | Multipurpose Internet Mail Extensions |
| TTF | TrueType Font |
| OTF | OpenType Font |
| WOFF | Web Open Font Format |
| ODT | OpenDocument Text |
| ODS | OpenDocument Spreadsheet |
| ODP | OpenDocument Presentation |
Key Points to Remember Before Your Exam
- A file extension is the suffix after the dot in a filename (e.g., .docx, .jpg, .mp3) that tells the OS the file type and which program should open it.
- .docx = Word, .xlsx = Excel, .pptx = PowerPoint – the ‘x’ in all three stands for XML (introduced with Microsoft Office 2007).
- .doc, .xls, .ppt are the older binary Office formats (used in Office 97–2003); .docx, .xlsx, .pptx are the newer XML-based formats.
- .odt, .ods, .odp are the LibreOffice / OpenDocument open-standard equivalents of Word, Excel, and PowerPoint.
- .pdf was created by Adobe Systems (John Warnock, 1993) – Portable Document Format; preserves formatting on all devices.
- .jpg uses lossy compression (some quality lost); .png uses lossless compression (no quality lost); .png supports transparency.
- .gif supports simple frame-based animation and is limited to 256 colors.
- .bmp is an uncompressed Microsoft bitmap format – highest quality but very large file size.
- .svg is a vector image format (XML-based) – scales to any size without quality loss; used for logos and icons.
- .mp3 was developed by Fraunhofer Society (Germany) and standardized by MPEG in 1993.
- .flac is a lossless audio format – no quality loss; preferred by audiophiles over .mp3.
- .wav is an uncompressed audio format by Microsoft and IBM – CD quality; very large files.
- .mp4 is the most widely used video format today – good quality with small file size.
- .zip was created by Phil Katz (PKZIP, 1989); .rar uses better compression but requires WinRAR or 7-Zip.
- .iso is a disc image – an exact byte-for-byte copy of a CD/DVD; used to distribute OS installers.
- .exe (Windows), .apk (Android), and .ipa (iOS) are executable/installer files; .apk from unknown sources poses a security risk.
- .dll (Dynamic Link Library) is a shared Windows system file loaded by .exe programs; critical OS files.
- .bat and .vbs are scripting files on Windows; .vbs is frequently used in malware phishing attacks.
- MIME (Multipurpose Internet Mail Extensions) types tell browsers how to handle files served over the internet (e.g., image/jpeg, application/pdf).
- Double extension attack: photo.jpg.exe appears as ‘photo.jpg’ on Windows if ‘hide known extensions’ is enabled – a common malware trick.
Frequently Asked Questions
What is the difference between .doc and .docx?
.doc is the older Microsoft Word file format used in Office 97 through Office 2003. It is a binary format, meaning it stores data as raw binary code. .docx is the modern Microsoft Word format introduced with Office 2007. It is based on Open XML – a ZIP-compressed package of XML files. .docx files are typically smaller than equivalent .doc files, are more reliable (less prone to corruption), and are the default format in all versions of Word from 2007 onward. The ‘x’ in .docx explicitly stands for XML. Similarly, .xls became .xlsx (Excel) and .ppt became .pptx (PowerPoint) in Office 2007.
What is the difference between lossy and lossless compression in image files?
Lossy compression permanently removes some image data during compression to achieve a smaller file size. The quality loss is usually imperceptible at moderate compression levels, but becomes visible at high compression. JPEG (.jpg) is the most common lossy image format. Each time you save a JPEG, it loses a little more quality. Lossless compression reduces file size without discarding any data – the original image can be perfectly reconstructed from the compressed file. PNG is the most common lossless image format for web use. BMP is uncompressed (no compression at all). For photographs where some quality loss is acceptable: use JPG. For graphics, logos, screenshots, and images requiring transparency: use PNG.
What is the difference between .zip, .rar, and .7z archive formats?
.zip is the most universal archive format, created by Phil Katz in 1989. It is natively supported in Windows, macOS, and Linux – no extra software needed. Compression ratio is good but not the best. .rar (Roshal Archive) generally achieves better compression ratios than ZIP, especially for large files. It requires WinRAR or 7-Zip to create and extract, and WinRAR is commercial software. It supports splitting archives into multiple parts. .7z is an open-source format from the 7-Zip project. It offers the best compression ratio of the three, supports strong AES-256 encryption, and is completely free. Both .rar and .7z require additional software to open. For most everyday use: ZIP. For maximum compression: 7z. For splitting large files across discs: RAR.
Which image format should be used for logos and icons on websites?
SVG (Scalable Vector Graphics) is the best format for logos and icons on websites. SVG is a vector format – it stores shapes, paths, and coordinates mathematically rather than as pixels. This means it scales to any size (from a tiny favicon to a huge billboard) with absolutely no loss of quality. SVG files are also XML-based, so they can be styled with CSS and animated with JavaScript. For simple icons on the web, .png is the second choice when SVG is not possible, because PNG supports transparency. JPEG is not suitable for logos because it does not support transparency and shows compression artifacts around sharp edges.
What makes .exe files dangerous from a security perspective?
An .exe (executable) file contains machine code that the Windows operating system will directly execute when opened. Unlike a document or image, which is just data that a program reads, an .exe file IS the program – it can do anything the user’s account permits: install software, delete files, connect to the internet, encrypt your hard drive (ransomware), or silently run in the background. Attackers exploit this by disguising .exe files as innocent-looking files using double extensions (photo.jpg.exe), fake icons, or misleading names. Email providers like Gmail and Outlook block .exe attachments entirely for this reason. Security best practice: never run an .exe from an untrusted source, always verify the source of downloaded programs, and keep your antivirus updated.
What is a MIME type and where is it used?
MIME stands for Multipurpose Internet Mail Extensions. Originally designed for email attachments, MIME types are now used across the web. A MIME type is a two-part label in the format type/subtype (e.g., image/jpeg, text/html, application/pdf) that tells the receiving system what kind of data a file contains. Web servers include the MIME type in the Content-Type header of every HTTP response. The browser uses this to decide how to handle the file: render it as HTML, display it as an image, play it as audio, open a PDF viewer, or prompt a download. Sending the wrong MIME type causes browsers to mishandle files – a server sending an HTML file with the MIME type text/plain would display the raw HTML code instead of rendering the web page.
What is the .iso format and how is it used?
An .iso file is a disc image – an exact, sector-by-sector copy of the entire contents of a CD, DVD, or Blu-ray disc stored as a single file. The name comes from the ISO 9660 file system standard used on optical discs. ISO files are used to distribute operating systems (Windows, Ubuntu Linux), software installers, and bootable recovery tools. Instead of physically burning a disc, users can mount the .iso file as a virtual drive in Windows (built-in since Windows 8) or macOS, or use it to create a bootable USB drive. ISO files are also used to preserve old software and games that were originally distributed on physical media.
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Practice MCQs – File Extensions
1. Which file extension is used for Microsoft Excel spreadsheets in Office 2007 and later?
A) .xls
B) .xlsx
C) .ods
D) .csv
Answer: B – .xlsx is the XML-based Excel format introduced with Office 2007. The ‘x’ stands for XML.
2. PDF stands for:
A) Portable Data File
B) Print Document Format
C) Portable Document Format
D) Public Document File
Answer: C – PDF (Portable Document Format) was created by Adobe Systems in 1993.
3. Which image format supports transparency (alpha channel) and uses lossless compression?
A) JPEG
B) BMP
C) GIF
D) PNG
Answer: D – PNG (Portable Network Graphics) supports full alpha transparency and uses lossless compression.
4. JPEG stands for:
A) Joint Photographic Expert Group
B) Joint Photographic Experts Group
C) Joint Picture Encoding Group
D) Java Photographic Encoding Group
Answer: B – JPEG stands for Joint Photographic Experts Group – the committee that created the standard.
5. Which audio format provides lossless audio compression with no quality loss?
A) MP3
B) AAC
C) FLAC
D) WMA
Answer: C – FLAC (Free Lossless Audio Codec) compresses audio without any quality loss.
6. Which file extension represents an Android application installer?
A) .exe
B) .ipa
C) .apk
D) .app
Answer: C – .apk (Android Package Kit) is the file format for Android app installation packages.
7. The ‘x’ in .docx, .xlsx, and .pptx stands for:
A) Extension
B) Extra
C) XML
D) Express
Answer: C – The ‘x’ stands for XML; these formats are based on the Open XML standard introduced in Office 2007.
8. Which image format is a vector format that scales without any loss of quality?
A) PNG
B) JPEG
C) BMP
D) SVG
Answer: D – SVG (Scalable Vector Graphics) is a vector format; it scales infinitely without quality loss.
9. Which archive format natively built into Windows requires no additional software to open?
A) RAR
B) 7Z
C) ZIP
D) TAR
Answer: C – ZIP is natively supported in Windows, macOS, and Linux without any additional software.
10. An .iso file is best described as:
A) A compressed image format
B) An executable installer
C) A disc image – an exact copy of a CD/DVD stored as a single file
D) An international standard video format
Answer: C – .iso is a disc image (ISO 9660 standard); an exact byte-for-byte copy of an optical disc.
11. Which video format is the most widely used on the internet and across all devices today?
A) AVI
B) WMV
C) MKV
D) MP4
Answer: D – .mp4 (MPEG-4) is the most universally supported video format across devices and platforms.
12. Which file extension is a Windows executable that can directly run programs?
A) .dll
B) .exe
C) .sys
D) .bat
Answer: B – .exe (Executable) files are directly run by Windows to launch programs.
13. The .odt file format is associated with which office suite?
A) Microsoft Office
B) Google Workspace
C) LibreOffice
D) Apple iWork
Answer: C – .odt (OpenDocument Text) is the default word processor format of LibreOffice Writer.
14. MIME stands for:
A) Multiple Internet Mail Extensions
B) Multipurpose Internet Mail Extensions
C) Multiple Image and Media Encoding
D) Multipurpose Image and Media Extensions
Answer: B – MIME stands for Multipurpose Internet Mail Extensions.
15. Which is an example of a double extension security attack?
A) photo.png saved as photo.jpg
B) document.docx opened in LibreOffice
C) photo.jpg.exe appearing as ‘photo.jpg’ when file extensions are hidden
D) video.mp4 renamed to video.avi
Answer: C – photo.jpg.exe is a classic double extension attack; if Windows hides known extensions, users see only ‘photo.jpg’ but the file is actually an executable.