What Is a .dmg File? .dmg Format, MIME & How to Open

Quick facts

Extension.dmg

File typemacOS Disk Image

MIME typeapplication/octet-stream

CategoryData & Text

Charset—

CompressibleYes

Format familydisk

What is .dmg

What is a .dmg file?

A .dmg file is a macOS Disk Image — Apple disk image used to distribute macOS software.

In the mime-db registry it maps to application/octet-stream, and it is marked as compressible. When serving .dmg over HTTP, set the Content-Type header as shown in Developer info below.

Related entities: it maps to application/octet-stream — and is delivered over HTTP via the Content-Type header.

How to open .dmg files

Use macOS or 7-Zip to open and edit .dmg files.
Any text editor (Notepad, VS Code) can inspect the raw content as text.

Developer info

When served over HTTP, responses should set the following header:

Content-Type: application/octet-stream

Common software that reads/writes .dmg:

macOS7-Zip

Relation chain

.dmgextension of

format

diskserved as

mime type

application/octet-streamsent via header

http header

Related extensions

Related MIME types

application/octet-stream

.bin .dms .lrf

application/x-apple-diskimage

.dmg

Common uses

Configuration files
Data interchange between systems
API request and response payloads
Logs and data exports

How to edit .dmg files

Open the file with macOS, make your changes and save.
Most editors preserve the original formatting and encoding — avoid changing the charset.

How to create .dmg files

Create a new file and save it with the .dmg extension, or export this format from macOS.

Frequently asked questions

What programs can open .dmg files?

Common options include macOS, 7-Zip. You can also open many of these files with built-in viewers or a browser.

How do I create a .dmg file?

Create a new file in any text editor or the app that owns the format and save it with the .dmg extension.

What is the relationship between .dmg and the application/octet-stream MIME type?

application/octet-stream is the media type identifier used for .dmg files during network transfer (for example in the HTTP Content-Type header).

Sources & standards

Updated 2026-09-13

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