[2015 iMac] Would an internet factory restore to El Capitan from Catalina also downgrade the system firmware?

[antnythr]

I've got a 2015 iMac that I was going to do an internet restore on to the version of MacOS that came with the system (10.11). Currently on 10.15.5. I have a WD SN750 NVME drive inside that required an update to High Sierra originally to update the firmware so that the drive could be used.

If I downgrade while doing an internet restore, would it also downgrade the system firmware or does it just leave the system with the currently installed firmware?

 

[chrfr]

I've got a 2015 iMac that I was going to do an internet restore on to the version of MacOS that came with the system (10.11). Currently on 10.15.5. I have a WD SN750 NVME drive inside that required an update to High Sierra originally to update the firmware so that the drive could be used.

If I downgrade while doing an internet restore, would it also downgrade the system firmware or does it just leave the system with the currently installed firmware?

The firmware cannot be downgraded.

 

[antnythr]

Thanks for the response. I was worried about the possibility that I'd end up with a system that couldn't boot unless I opened it up and put the factory SSD back in.

 

[chrfr]

Thanks for the response. I was worried about the possibility that I'd end up with a system that couldn't boot unless I opened it up and put the factory SSD back in.

You'll want to confirm that NVMe boot support exists in 10.11 before you do this. I'm not sure that it's there.

 

[pldelisle]

But why return as far as 10.11?
If stability is the main concern, Mojave is better. Plus you will still have application support, while 10.11 is deprecated from a long time ago...

Never had a problem with Catalina 10.15.3+. Try maybe reinstalling it as a brand new Mac with Catalina 10.15.5. It might solve all your problems.

 

[antnythr]

You'll want to confirm that NVMe boot support exists in 10.11 before you do this. I'm not sure that it's there.

Turns out that 10.11 installer doesn't even see the NVME drive.

But why return as far as 10.11?
If stability is the main concern, Mojave is better. Plus you will still have application support, while 10.11 is deprecated from a long time ago...

Never had a problem with Catalina 10.15.3+. Try maybe reinstalling it as a brand new Mac with Catalina 10.15.5. It might solve all your problems.

I found an old 10.6 DVD the other day and got interested in trying out old versions of MacOS. Unfortunately 10.6 wouldn't install in Fusion (apparently the license doesn't permit virtualization), so I then decided to try out the original version that came with this iMac (my first Mac computer). I bought it used in January of this year and never actually had an opportunity to use any versions of MacOS earlier than High Sierra.

Restored my time machine backup and I'm back on 10.15.5.