dmg

.dmg — Apple Disk Image

Apple Inc. · 1999

Developer
Apple Inc.
Category
Disk Images
MIME Type
application/x-apple-diskimage
First Released
1999
Open Format
No
File Signature
koly
At a Glance
.dmg
Apple Disk Image

A DMG file is an Apple Disk Image file primarily used on macOS operating systems.

Reviewed on April 28, 2026
Compression
Compressed
Transparency
N/A
Editability
Low
Best for
packaged disk content

Key Features

  • Compressed storage behavior for typical disk workflows
  • Common MIME type: application/x-apple-diskimage
  • Recognizable file signature: koly
  • Associated with Apple Inc.

Best For

  • Exact packaged distributions
  • Mountable media
  • Installer delivery

Less Ideal For

  • Casual inline editing
  • Simple photo sharing
  • Direct browser-native consumption

Common Use Cases

  • Mounting disk images
  • Software distribution
  • System backups or installers

How to Open It

  1. On Windows, open the file with 7-Zip or TransMac.
  2. On macOS, open the file with Disk Utility or Finder.
  3. If the file does not open, confirm that the extension really matches .dmg and that the download or transfer completed without corruption.

What is a .dmg file?

A DMG file is an Apple Disk Image file primarily used on macOS operating systems. It functions as a virtual disk, containing software installers, applications, or compressed data. Users can mount a DMG file as a physical disk, allowing easy access to its contents.

Programs That Open .dmg Files

PlatformProgram
Windows7-ZipFree
TransMacPaid
DMG ExtractorPaid
macOSDisk UtilityFreeOfficial
FinderFreeOfficial

Common Problems with .dmg Files

⚠️ DMG file won't open on Windows.
DMG files are native to macOS. Use third-party tools like 7-Zip or TransMac on Windows to extract or convert them, or a virtual machine running macOS.
⚠️ Corrupted DMG file.
A corrupted DMG might not mount or extract. Re-download the file from its source. If you created it, try re-creating it using Disk Utility or a reliable archiving tool.

Frequently Asked Questions

What is a DMG file used for?▼

DMG files are primarily used on macOS for distributing software applications, storing compressed data, and creating bootable disk images. They act like virtual disks that can be mounted.

Can I convert a DMG file to ISO?▼

Yes, you can convert DMG to ISO, especially for compatibility with other operating systems. On macOS, you can use Disk Utility or the `hdiutil` command-line tool. On Windows, several third-party converters are available.

Are DMG files safe?▼

Generally, DMG files themselves are a secure container format. However, like any executable or archive, the *contents* of a DMG can be malicious. Always download DMG files from trusted sources and use antivirus software.

Technical Details

DMG files typically use HFS+ or APFS file systems and can include compression, encryption, and checksumming. They often start with a signature like 'koly' (for UDRW) or contain specific data structures that identify them as Apple Disk Images.

Did You Know?

The 'DMG' extension originally stood for 'Disk Image' and replaced the older .IMG and .SIT (StuffIt) formats for software distribution on Mac.

Security Information

DMG files are commonly used for legitimate software distribution. However, like any executable file, they can potentially contain malware. Always download DMG files from trusted sources and scan them with antivirus software before opening.

Related Extensions

.ISO