DMG vs ZST
A detailed comparison of Apple Disk Image and Zstandard Compressed — file size, quality, compatibility, and which format to choose for your workflow.
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Technical Specifications
| Specification | .DMG | .ZST |
|---|---|---|
| MIME type | application/x-apple-diskimage | application/zstd |
| Extension | .dmg | .zst |
| Container types | UDIF (Universal Disk Image Format) | — |
| Compression | UDCO (zlib), UDBZ (bzip2), UDZO (LZMA), ULMO (LZMA) | — |
| Encryption | AES-128 or AES-256 | — |
| Algorithm | — | LZ77 variant + entropy coding (FSE/Huffman) |
| Standard | — | RFC 8478 (2018) |
| Compression levels | — | 1-22 (plus negative "fast" levels) |
Strengths Comparison
.DMG 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).
.ZST Strengths
- Extremely fast decompression (~2 GB/s on modern CPU).
- Scalable: very fast at level 1, near-xz ratios at level 22.
- Dictionary support for small-payload efficiency.
- Multi-threaded by default.
- Standardized (RFC 8478), BSD-licensed reference.
Limitations
.DMG — 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.
.ZST — Limitations
- Newer than gzip/bzip2 — some legacy tools still lack support.
- At extreme compression levels, xz can still win on ratio.
- Memory usage at high levels is significant.
- Consumer archiving tools (Windows Explorer) lag behind.
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.
ZST (Zstandard Compressed) 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. ZST 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.
7-Zip, WinRAR, The Unarchiver (macOS), and the built-in archive utilities on Windows and macOS open most ZST files. For command-line extraction, 7z, unar, or the format-specific tool handles ZST cleanly. If your extractor does not recognise ZST, 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.
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