About DMG Files
Apple Disk Image
DMG (Apple Disk Image) is the standard disk image format on macOS for distributing software. It can contain a complete file system with compression and optional encryption, and supports internet-enabled auto-mounting for seamless app installation.
Family
Archives & Compressed
Extension
.dmg
MIME Type
application/x-apple-diskimage
Can Use As
HOW DMG
CAME TO BE.
DMG — Apple Disk iMaGe — replaced the older .img and .sit formats when Apple shipped Mac OS X Server 1.0 in 1999. A .dmg is a read-only, usually compressed disk image that mounts on macOS as if it were a real volume: the user drags the app icon from the mounted volume to the Applications folder and that's the install.
DMGs can be plain disk images, zlib-compressed (UDCO), bzip2-compressed (UDBZ), or LZMA-compressed (UDZO/ULMO). Modern DMGs from Apple’s App Store are ZFS-like compressed variants. Every third-party macOS app distributed outside the App Store ships as a DMG with a custom background, volume icon, and an arrangement arrow telling the user to drag the app into Applications. It’s a signature macOS aesthetic.
CURIOSITIES &
TRIVIA.
The custom DMG background with a pointing arrow telling you "drag the app to Applications" is a macOS cultural signature — invented by no one officially, copied by every indie Mac app.
DMG files can be password-protected via AES-128 or AES-256 encryption — the Finder prompts for the password when mounting.
Apple ships all its non-App Store downloads as DMGs: Xcode, Safari beta, macOS installers, Pages/Keynote.
A DMG can contain multiple partitions, EFI boot sectors, and be bootable — Recovery DMGs use this.
The container format is proprietary but documented enough that tools like dmg2img on Linux can extract most DMGs.
STRENGTHS &
LIMITATIONS.
Strengths
- Universal macOS distribution format since 1999.
- Compressed or encrypted variants available.
- Can be bootable (used by recovery and installer DMGs).
- Custom backgrounds and layout create polished installer experience.
- Preserves Mac-specific filesystem metadata (extended attributes, resource forks).
Limitations
- macOS-only — Windows and Linux need third-party tools.
- Proprietary container with limited public documentation.
- File sizes are often larger than equivalent ZIP or 7z.
- Opaque to most antivirus and malware-scanning pipelines.
Typical Sizes & Weights
Small macOS app
5-30 MB
Xcode installer
~12 GB
macOS installer (full)
12-15 GB
Technical Specifications
- MIME type
- application/x-apple-diskimage
- Extension
- .dmg
- Container types
- UDIF (Universal Disk Image Format)
- Compression
- UDCO (zlib), UDBZ (bzip2), UDZO (LZMA), ULMO (LZMA)
- Encryption
- AES-128 or AES-256
CONVERT FROM
DMG
Common Use Cases
macOS software distribution, application installers, encrypted disk images
Related Formats
Popular comparisons
DMG vs ZIP
Differences, file size, and when to choose each format.
DMG vs 7Z
Differences, file size, and when to choose each format.
DMG vs TAR
Differences, file size, and when to choose each format.
DMG vs GZ
Differences, file size, and when to choose each format.
DMG vs BZ2
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DMG vs XZ
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Popular DMG conversions
The most-requested destinations when starting from DMG.
Frequently Asked Questions about DMG
Frequently Asked Questions
DMG (Apple Disk Image) is an archive format used to bundle multiple files and folders into a single compressed file. The archive preserves the directory structure and typically reduces total size via compression. DMG sits in the archives & compressed family and has specific strengths around compression ratio, speed, or platform support.
7-Zip, WinRAR, The Unarchiver (macOS), and the built-in archive utilities on Windows and macOS open most DMG files. For command-line extraction, 7z, unar, or the format-specific tool handles DMG cleanly. If your extractor does not recognise DMG, convert to ZIP first — ZIP opens on every operating system without extra software.
Upload the DMG to KaijuConverter and pick ZIP, 7Z, TAR.GZ, or RAR as the target. Our pipeline extracts the original archive and re-compresses the contents into the target format. File permissions, timestamps, and directory structure are preserved where both formats support them.
Depends on the goal. ZIP is the universal baseline — every OS extracts it out of the box. Formats like 7Z or TAR.GZ compress better but require specific tools. DMG may win on compression ratio, password support, or OS integration for specific workflows; ZIP wins on raw compatibility.