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Disk images (.dmg)

Purrchiver doesn’t open .dmg files. They aren’t archives — they’re macOS disk images, which is a different category. Here’s what they are and how to use them.

What a DMG is

A DMG (UDIF — Universal Disk Image Format) is a file that contains a complete filesystem image — what you’d see if you formatted a disk and copied files onto it. macOS treats them like virtual disks: when you double-click one, the system mounts it as if you plugged in a USB drive. The contents show up in Finder as a mounted volume you can browse and drag from.

Apps you download from the web on macOS usually come as DMGs. You mount the DMG, drag the app to /Applications, unmount the DMG. It’s the standard distribution method outside the App Store.

How to open one

Double-click in Finder. The DMG mounts as a volume on your Desktop / in Finder’s sidebar. Browse it, drag what you need out, then eject it:

  • Drag the volume to Trash, or
  • Select the volume and press ⌘E, or
  • Right-click the volume → Eject

If double-click doesn’t work — usually because the DMG file is corrupt or was downloaded incompletely — open Disk Utility (in Applications → Utilities) and use File → Open Disk Image… to inspect what’s wrong.

Why Purrchiver doesn’t handle them

Purrchiver is an archive utility — it handles formats like ZIP, 7z, tar, RAR. Disk images are managed by macOS itself via hdiutil and Disk Utility. Purrchiver could shell out to those tools to mount and copy contents, but that’s a noticeably different workflow from “extract this archive” and would likely confuse users about what kind of file they’re working with.

A v1.1 feature on the roadmap is an explicit “Open DMG” affordance that mounts via hdiutil and copies contents to a folder — if that lands, the friendly error you’re seeing now will be replaced by that workflow. For v1.0, double-click in Finder is the recommended path.

What about .iso?

.iso files are a different beast. There are two cases:

  1. Bootable ISOs (Linux distro install media, etc.) — macOS mounts these natively, just like DMGs. Double-click in Finder.
  2. Data ISOs (data discs, archived CD/DVD content) — Purrchiver does read these, treating them as ISO 9660 archives. Drag onto Purrchiver to extract.

If you’re not sure which one you have, just try Purrchiver first — if the file is bootable, you’ll get a friendly error pointing you to double-click instead.