Types of images in System Image Utility on Mac
You use System Image Utility to create network images, which are folders ending with an .nbi extension. Network images contain essential files that start a Mac over an Ethernet network. You can create four types of network images with System Image Utility:
NetBoot: A NetBoot network image allows you to start several Mac computers over an Ethernet network using the NetInstall service of the Server app. See Create NetBoot images.
NetInstall: A NetInstall network image allows you to install macOS on Mac computers over an Ethernet network. See Create NetInstall images.
NetRestore: A NetRestore network image allows you start up a Mac and quickly replace the entire contents of the internal startup volume. See Create NetRestore images.
NetInstall without an operating system: A NetInstall network image that contains configuration profiles, scripts, or packages, but no operating system. See Create package-only images.
Using NetBoot, NetInstall, and NetRestore network images, your Mac computers can start from a standardized macOS configuration suited to specific tasks. Because the Mac computers start from the same network image, you can quickly update macOS for users by updating a single disk image or volume.
NetBoot, NetInstall, and NetRestore network images each contain a disk image and other files necessary for the Mac to start up. You shouldn’t edit these files. Doing so may make the image unusable.
You can set up different NetBoot or NetInstall network images to suit the needs of specific computer models, such as a group for MacBook computers and a group for iMac computers.