DMG vs GZ
A detailed comparison of Apple Disk Image and Gzip Compressed — file size, quality, compatibility, and which format to choose for your workflow.
Apple Disk Image
Archives & CompressedDMG (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.
About DMG filesGzip Compressed
Archives & CompressedGzip is a single-file compression format based on the DEFLATE algorithm. It is most commonly paired with TAR to create .tar.gz archives and is the standard compression for web content delivery.
About GZ filesStrengths 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).
GZ Strengths
- Patent-free, royalty-free — that was the whole point in 1992.
- Universally supported on every OS.
- Fast compression and extremely fast decompression.
- Preserves original timestamps and filenames in the header.
- Streamable — can compress/decompress over pipes.
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.
GZ Limitations
- Compresses one file at a time — needs tar for multi-file archives.
- Older algorithm — Zstandard, xz, and brotli all beat it on ratio.
- Single-threaded in the reference implementation (pigz fixes this).
- Not as aggressive as modern codecs on highly redundant data.
Technical Specifications
| Specification | DMG | GZ |
|---|---|---|
| MIME type | application/x-apple-diskimage | application/gzip |
| Extension | .dmg | — |
| Container types | UDIF (Universal Disk Image Format) | — |
| Compression | UDCO (zlib), UDBZ (bzip2), UDZO (LZMA), ULMO (LZMA) | — |
| Encryption | AES-128 or AES-256 | — |
| Extensions | — | .gz, .tgz (with tar) |
| Algorithm | — | DEFLATE (LZ77 + Huffman coding) |
| Standard | — | RFC 1952 (gzip), RFC 1951 (DEFLATE) |
| Header | — | 10 bytes: magic, method, flags, mtime, extra, filename, comment, crc, isize |
Typical File Sizes
DMG
- Small macOS app 5-30 MB
- Xcode installer ~12 GB
- macOS installer (full) 12-15 GB
GZ
- Plain text file 25-40% of original
- HTML page 20-30% of original
- Source code archive 15-30% of original
- Already-compressed file (JPEG, MP4) 99-100% (no gain)
Ready to convert?
Convert between DMG and GZ online, free, and without installing anything. Encrypted upload, automatic deletion after 60 minutes.
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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.
GZ (Gzip 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. GZ 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 GZ files. For command-line extraction, 7z, unar, or the format-specific tool handles GZ cleanly. If your extractor does not recognise GZ, 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.