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Bridging_the_gap.md

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Bridging the macOS compatibility gap when using OpenCore Legacy Patcher

Problem description

As you may know, OpenCore Legacy Patcher utilizes virtualization technology introduced in macOS Big Sur 11.3 to make it "think" that it is running in a virtual environment. Combined with a Booter patch to skip board-id checks, this allows installing newer versions of macOS on unsupported systems without the need to change the SMBIOS. Not having to change the SMBIOS is crucial for running newer versions of macOS on real Apple Macs. Because otherwise you run into all sorts of hardware related issues on these machines.

On Wintel systems it's not a big deal. Still, the overall performance of your system, especially CPU and GPU power management is best if you are using an SMBIOS that matches your CPU family.

What is this gap you are yapping about?

Since the virtualization technology cannot be utilized prior to Big Sur 11.3, installing older versions of macOS requires another approach. So between macOS High Sierra and Big Sur, there's a macOS comaptibility gap of two OSes that cannot be installed easily, namely:

  • macOS Mojave (last macOS with 32 bit Intel support). Owners of a real Mac can use Mojave Patcher to install it.
  • macOS Catalina (slimmest macOS since it only contains 64 bit Intel code). Owners of a real Mac can use Catalina Patcher to install it.

Bridging the Gap

The following Settings need to be changed in your config.plist to install macOS prior to Big Sur 11.3. This mainly concerns SMBIOS, SIP and APFS driver settings:

Section  Setting
SMBIOS Pick a suitalbe SMBIOS for your machine and the OS you want to run based on this chart and adjust PlatFormInfo/Generic/SystemProductName accordingly.
SIP Change csr-active-config as well:
  • macOS 10.11 and 10.12: 67000000
  • macOS 10.13: EF030000
  • macOS 10.14/10.15: EF070000
  • macOS 11+: 03080000
UEFI In order for the APFS driver to load in older versions of macOS (everything prior to macOS Big Sur), you need to change the following settings in UEFI/APFS, otherwise the partitions with the older macOS won't be displayed in the boot menu:
  • MinDate: -1
  • MinVersion: -1
NVRAM Add to boot-args: -no_compat_check

Tip

  • Additional steps may be required to get it working (device-id of the iGPU or switching Wi-Fi/Bluetooth kexts, etc.).
  • As a precaution, create a backup of your current EFI folder on a FAT32-formatted USB drive. Edit the configuration on the USB drive and boot from it. This way, you can make changes without affecting your main system. If the changes cause issues, you can simply reboot from your hard drive or SSD.
  • To ensure that you are really booting from your USB flash drive you might want to use a different theme for it so to seperate it visually from the one on your hdd/ssd