Apple no longer lists High Sierra in the "Purchased" tab of the Mac App Store for most users, but you can still get the installer directly from Apple’s support website.
If a Mac suffers severe drive corruption or lacks an internet connection, a local bootable installer created from a DMG bypasses internet recovery bottlenecks.
Although Apple has moved on to newer operating systems, many users still need to for older Mac support, virtual machines (VMware/VirtualBox), or creating bootable USB installers.
The .dmg (Disk Image) file is the complete, bootable installer for macOS. It functions as a "digital Swiss Army knife"—a portable, mountable container that packages the full operating system. It is essential if you want to:
Matching these hashes provides strong evidence that your file is authentic and uncorrupted.