I didn't need new firmware to upgrade to Sierra. Obviously, I do need newer firmware if I want to upgrade to High Sierra or Mojave.

If I upgrade the firmware to the newest available, will I lose the ability to boot into any older OSs?

Not in my experience.

Quote
anonymouse1
Not in my experience.

You gain NVMe use, improved graphics compatibility (allegedly), etc.
Upgrading the firmware does not require an OS update.
Dosdude1 is our friend! [dosdude1.com]

btw, I am not an expert just experienced

(now if there was just a way to upgrade those SATA-II & USB 2 busses without
add-on cards!)

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Edited 1 time(s). Last edit at 07/24/2020 04:41AM by MrNoBody.

Quote
MrNoBody

Quote
anonymouse1
Not in my experience.

You gain NVMe use, improved graphics compatibility (allegedly), etc.
Upgrading the firmware does not require an OS update.
Dosdude1 is our friend! [dosdude1.com]

btw, I am not an expert just experienced

(now if there was just a way to upgrade those SATA-II & USB 2 busses without
add-on cards!)

Thanks for that link. I think I'm going to try out his QuickNAS

Post results, por favor. Gracias.
==

Anyone have a link to the process for installing a firmware upgrade without installing Mojave?

---

My life goes smoothly and in regular intervals

ka jowct, make sure you have the full "Install macOS Mojave.app" (6GB)
and a Metal supported graphics card.

Short tutorial video @ YouTube.

btw I did this a few months back, results in Boot ROM Version: 144.0.0.0.0.

---

39°36'17"N 75°44'43"W

DuckDuckGo
The search engine that doesn't track you.

DemComm Records 2021 Greatest Hits
includes:
Taxman by Joe & Nancy's Rich Ice Cream Band
The Humpty Dance by The Harris-Brown Hookup
Lets Spend The Night Together by The Fang-Swalwell Gang
Díaz-Canel Is A Friend of Ours by The AOC Squad
My Old Kentucky Retirement Home by MitchMcC & The Soggy Boxer Boys
Burning Down The House by Merrick & The Goons
Back In the USSR by Bernie's Red Square Trio

Quote
MrNoBody
ka jowct, make sure you have the full "Install macOS Mojave.app" (6GB)
and a Metal supported graphics card.

Short tutorial video @ YouTube.

btw I did this a few months back, results in Boot ROM Version: 144.0.0.0.0.

That video needs either some serious audio work or closed caption subtitles. I can't hear a darn word.

thanks for asking this question... I've had the same one. I'll be following this...

If anyone is still following this, the answer is no, you do not lose the ability to boot into older OSs.

I haven't actually done the upgrade(s), but I have done a lot of reading and the experts say you can still go back as far as the machine supports. For example, a 5,1 can go back to 10.6.4. The only caveat is if you install a metal-compatible video card (which is a much newer card), those older OSs won't work with the card.