EFI Upgrade does prevent El Capitan booting anymore?

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8 points

EFI Upgrade does prevent El Capitan booting anymore?

Hi,

please help me with one question. If I upgrade to Catalina (10.15.4) from El Capitan (10.11.6) I understand the EFI will be upgraded from version 71.0178.B00 to 72.193.0.0.0.0 (it will be upgraded to this version since High Sierra actually). So after I upgrade to this EFI version, am I able to boot anymore El Capitan?

Details:

MacBook Air 13 inch Early 2105

i5 1.6Ghz 8Gb RAM MacBookAir7.2

Boot ROM: MBA71.0178.B00

SMC version: 2.27f2

I am stuck with El Capitan due to some music plugins that are exclusive to this version. Can't upgrade. Last week I've upgraded my SSD from 128GB to 960GB, but since I am stuck with El Capitan, I used an AHCI Gen3 x2.

My idea is to keep this SSD in an thunderbolt adaptor and boot El Capitan when I need to make music, and use an Gen3 x4 SSD with NVMe as internal SSD, but this forces me to update at least to High Sierra, because the EFI upgrade brings compatibility with that drive.

My concern is once I upgrade the EFI to 72.193.0.0.0.0, am I able to still boot the external thunderbolt AHCI drive with El Capitan?

Thank you for your time,

Vlad

Posted on May 2, 2020 6:18 AM

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Answer 1

Top-ranking reply

Wraymogg Author

Level 1

8 points

May 31, 2020 2:45 PM in response to a brody

Brody thank you for trying to help me, but you didn't get at all what I was trying to do.

So I risked it, did it and everything payed off.

If anyone is in the same conundrum, this is what I did:

I switched to the original SSD and upgraded to High Sierra
After that, it took two updates and one of them flashed my EFI. Before it was MBA71.0178.B00, after flashing it is 193.0.0.0.0 (the EFI is beeing flashed ONLY if the original SSD is installed)
Now with the new EFI, my new Transcend JetDrive 850 Gen3 x4 NVMe is seen by my MacBook Air
Booted from High Sierra disk, re-partitioned the 850 drive, formatted it AFPS then installed brand new High Sierra on it.
My old Transcend JetDrive 825 Gen3 x2 AHCI I installed it in the JetDrive 855's Thunderbolt 2 enclosure
I can confirm that the new EFI 193.0.0.0.0 doesn't have any problem with the external drive that is an Gen3 x2 AHCI SSD with El Capitan installed, so now I can boot both High Sierra (internal SSD) and El Capitan (external Thunderbolt SSD).

I needed High Sierra, but everything applies for Mojave or Catalana too.

I hope this will be helpful.

Best regards,

Vlad

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Answer 2

a brody

Level 10

85,382 points

May 5, 2020 8:36 AM in response to Wraymogg

It is possible that it might not work. What you can do, is partition the SSD to have room for El Capitan, and then install Catalina on the unused partition.

Mind you, Catalina will probably reformat its own partition APFS, being it is an SSD. That means while booted into El Capitan, you won't be able to see the content of the Catalina partition. To reboot into Catalina, you'll need to use the Option key start on boot to select the Catalina partition.

Backup your data before installing anything new or partitioning.

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Answer 3

Wraymogg Author

Level 1

8 points

May 5, 2020 9:03 AM in response to a brody

Thank you for your reply.

I don't mind if I don't see Catalina partitions from El Capitan. Actually each of them will reside on their own SSD, so no need to cross partitions.

What I want is to be able to boot both Catalina and El Capitan from different SSDs.

My concern is about the EFI update that comes with Catalina. Once the ROM is written, will I still be able to boot El Capitan?

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Answer 4

a brody

Level 10

85,382 points

May 5, 2020 11:50 AM in response to Wraymogg

As long as the ROM wasn't written after Sierra's release there shouldn't be a problem. Where are you downloading the ROM from?

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EFI Upgrade does prevent El Capitan booting anymore?

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