When you mount and run the "Install macOS High Sierra" app from the official DMG (not the in-place updater), the installer does something impressive:
It converts your boot drive from HFS+ (Mac OS Extended) to APFS (Apple File System) without erasing your data, and without a separate partitioning step, all while running from a read-only DMG volume. macos high sierra 10136 dmg full
Once you have the macOS High Sierra 10136 dmg full (or the .app file), the most common use case is creating a bootable USB installer. This is essential for clean installations on unsupported or malfunctioning Macs. When you mount and run the "Install macOS
Once you have the .app file, you can create your own DMG for backup. It converts your boot drive from HFS+ (Mac
Apple released High Sierra in 2017, succeeding Sierra and preceding Mojave. While newer macOS versions (Catalina, Big Sur, Monterey, Ventura, and Sonoma) offer modern features, High Sierra is the last version of macOS to support certain legacy hardware.
Apple still provides a direct download for High Sierra via their support site:
You can also download MacOS High Sierra 10.13.6 from the Apple Support website: