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モデル番号A1419 / EMC 3070 / Mid 2017 / 3.4, 3.5もしくは3.8 GHz Core i5もしくは4.2 GHz Core i7 Kaby Lakeプロセッサ (ID iMac18,3) / Retina 5Kディスプレイ。システムは類似しているため、修理ガイドについては旧モデルのiMac Intel 27インチ Retina 5Kディスプレイ (Late 2014 & 2015) を参照してください。

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About 2017 iMac 27" and 2019 iMac 27" firmwares

Well as far as I could check through online research both the 2017 and 2019 models have the same hardware: same CPU socket, same GPU (ok, 580 vs 580pro, minor change) and same PSU however the 2017 model would not work with the same i9 9900 CPUs available for the 2019 models and I want to know why.

Could it be just a firmware restriction in the known 'Apple way' of planned obsolescence considering the hardware is the same therefore shouldn't be any technical reason? Would the 2017 model run with the i9 9900 CPUs if its firmware were to be flashed with 2019 firmware? Could the firmware even be actually flashed just like that…?

I would really like to know more than just assumptions ?

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Apple’s approach is to use the same firmware within a given ID Series so in your case the iMac17,1 and the iMac19,1

Late 2015 - Skylake

  • I5-6500
  • I5-6600
  • I7-6700K

2019 - Coffee Lake

  • I5-8500
  • I5-8600
  • I5-9600K

These are very different Intel CPU series which use very different micro-code. Apple does not load up their EFI with multiple micro-code builds.

Bottom line: You are limited to what the given series offered in some rare cases (very rare) you might have an option. Sadly not here.

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Let's just say for the sake of argument I get the EFI chip from a 2019 model and solder it to the 2017 board?

If both 2017 and 2019 have the same hardware wouldn't this 'unlock' the 2017 potential to run i9 CPUs same as the 2019?

Or is there anywhere else this micro-code is written in the hardware so it matches the required CPUs?

さんによる

I don't tempt fate!

Swapping over EFI chips between different hardware models is not something I would do.

Mod'ing requires a much deeper understanding of the design which is very difficult as Apple holds their cards quite tightly.

Time to crack open the Intel Architecture books to see what you can figure out. Warning that's about 3K of pages of stuff to dig through.

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@Carlos Ferrari Oh Carlos, if it were that simple. Remember that just because an EFI chip is changed over for the support of specific hardware, it doesn't mean that components down the line are also lined up to support "newer" hardware not planned for that version of the board.

I know for a fact that some boards within the same lineup (an obscure board manufacturer I used in the past for an employer) changed components to manage the higher frequency/voltages for newer hardware/CPUs and when we used unsupported CPUs with those older boards, we ended up borking a whole bunch of them in the field. It was a costly mistake from management.

さんによる

Well most of all it would be hard enough to get my hands on a 2019 EFI chip to begin with lol

It was mostly a thought exercise/wishful thinking I suppose. I do still believe it can be done but unless one can get a verifiable 2019 chip to replace the 2017 with and prove/unprove this will remain unknown…

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@Carlos Ferrari - Sorry I really think that's a very large pipe dream ;-{

Don't forget to score the answer and accept it - Thanks!

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You cannot use Coffee Lake CPU's (as in what the 2019 uses) on the 2017 for two (very) major reasons:

(1) The 2017 uses an LGA 1151 rev 1 socket, and the 2019 has the LGA 1151 rev 2.

(2) The chipsets on each logic board are very different: z170 vs z370

LGA 11551 rev1 vs rev2: Not same sockets: the pin allocations are different Second revision of the LGA 1151 socket for Coffee Lake CPUs:

"While physical dimensions remain unchanged, the updated socket reassigns some reserved pins, adding power and ground lines to support the requirements of 6-core and 8-core CPUs. The new socket also relocates the processor detection pin, breaking compatibility with earlier processors and motherboards. As a result, desktop Coffee Lake CPUs are officially not compatible with the 100 (original Skylake) and 200 (Kaby Lake) series chipsets."

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Edit:

In fact, there's a VERY detailed comparison of Kirby Lake/Coffee Lake pinouts (i.e. on the interface betwwen CPU and socket). And it explains the very big differences between the two. It even says a firmware upgrade would not be able to address it. The only (remote) possibility would be on some motherboards a z270 chipset is used, whicxh is closer to the z370. But iMac went from z170 to z370 directly.

Kabylake vs Coffee Lake LGA1151 Pinout Differences Revealed

Anadtech discusses it too:

Differences from Coffee Lake to Kaby Lake Physical Design: Pin Outs

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Chipsets: The 2017 logicboard has the z170 chipset, whereas the 2019 has the z370.

Here's a nice link on the differences between the chipsets (look under LGA 1151 rev1 and rev2).

List of Intel Chipsets

The z170 is quite different from the z370 in terms of what it supports.

And note that there was an intermediate z270 chipset in-between them, that is very close to the z370 (specs are very close here).

Intel says that the z170 cannot support the Coffee Lake CPU's (used in 2019 iMac):

LGA 1151

Look under the LGA 1151 rev1 and rev2 tables.

Can see that the z170 is not forwards compatible, and the z370 not backwards compatible, and even the z270 won't support Coffee Lake CPU's.

And this is part speculation on my end, but I think the EFI chips/firmware difference is not really an issue. You can both back-up and re-flash these chips on the board. And re-soldering one is no big deal: are simple chips, and you can buy them.

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@danj Just got my first 12 core 2013 Mac Pro yesterday. Will have a couple of questions on it for you later on, been a while since I had a new toy to play with. Simply Mac going under has really helped business, I'm actually making a living again.

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Carlos Ferrari さん、ありがとうございました！
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