Firmware

A firmware is an IPSW file that contains everything needed to run the core operating system of the respective device. Beta firmwares have also been released, but they require a valid Apple ID to acquire. To check for updates, iTunes/Finder/Apple Configurator/Apple Devices contacts https://s.mzstatic.com/version for iOS/iPod/Apple TV/HomePod mini IPSWs. There are different manifests for macOS IPSWs and bridgeOS IPSWs.