downgrade mac os mojave to high sierra without erasing

#Downgrade mac os mojave to high sierra without erasing install
#Downgrade mac os mojave to high sierra without erasing update
#Downgrade mac os mojave to high sierra without erasing full
#Downgrade mac os mojave to high sierra without erasing software

However, Apple limits this ability by removing its signatures from old restore files seven days after they have been superceded by a more recent version. In theory, Configurator’s revive process could be used to downgrade iBridge firmware.

#Downgrade mac os mojave to high sierra without erasing full

Full instructions are given in Configurator’s Help book.

#Downgrade mac os mojave to high sierra without erasing install

Following that, Internet Recovery (Command-Shift-Option-R) must be used to install macOS afresh.

#Downgrade mac os mojave to high sierra without erasing software

Restore is more extensive: in addition to updating iBridge firmware, this also erases internal storage, including the startup volume group, recoveryOS and supporting software on internal storage. The revive process simply updates iBridge firmware (Apple doesn’t mention accompanying EFI firmware, though), and doesn’t affect the System or Data volumes at all. All models with T2 chips run the same version of iBridge firmware (for a particular version of macOS), the same version of EFI firmware too, and they are normally updated at the same time.Īlthough the same basic rules for Intel Macs apply to those with T2 chips, models with T2 chips can have their firmware revived or restored if they’re put into DFU mode, connected by a USB-C to USB-C (charge only) cable to another Mac running Catalina or later, using Apple Configurator 2 (free from the App Store). Macs with T2 chips have firmware for that as well as normal EFI firmware, although because of its role in Secure Boot, attention is mainly paid to that for the T2, which is termed iBridge or bridgeOS.

#Downgrade mac os mojave to high sierra without erasing update

The firmware is intended to be ‘self-healing’, in that if an update goes wrong, the Mac should be able to restore functional firmware itself, although this appears to occur extremely infrequently. This only happens at the time of installation, though: mounting a bootable disk containing Monterey beta (which was installed on another Mac) doesn’t result in any firmware upgrade.įirmware updates aren’t provided outside macOS installers and updaters, and there’s no provision for downgrading EFI firmware. Thus, if the internal disk has Catalina installed and you then install Big Sur on an external disk mounted on that Mac, both the firmware and Recovery software is updated to that supplied with Big Sur. These can be inadvertently erased, forcing you to use Internet Recovery or Internet Diagnostics instead.įirmware, covering the firmware proper and Recovery tools, is updated to the latest version whenever a newer version of macOS is installed on any mounted disk, whether internal or external. They are both installed as disk images, named BaseSystem.dmg and AppleDiagnostics.dmg respectively, which are mounted and run from memory on demand. Although most of this is reliably updated by installing macOS updates, two components have in the past been vulnerable to failure, recoveryOS and AppleDiagnostics. These are based on a foundation of Intel’s UEFI, with Recovery tools written as UEFI apps and for a cut-down version of macOS known as recoveryOS. These models lack any support for Secure Boot, and rely on a combination of fixed ROM, upgradeable firmware, and software stored on the boot disk. The answer to these questions depends on which architecture your Mac has, and how it stores and maintains the different parts of what we loosely refer to as firmware. Let me ask you a simple question: supposing you installed the Monterey beta on an external disk, what would happen to that Mac’s firmware and its Recovery features? Given that Monterey is likely to bring firmware updates to most if not all Macs, how might that affect yours? That’s what I try to answer in this article – and it’s of great importance to all those who install beta-releases, as well as everyone considering upgrading in the autumn/fall.