iMac13,2 27" with firmware from 21.5" not seeing the 4 memory bays

People I wrote already that it happens also with other producers INCLUDING original HYNIX factory mounted RAMs. Relax a bit with Kingston, these are HyperX in reality if it sounds better and bring the topic on subject.

And just to prove the case:

http://dustinfarris.com/2013/01/16/2012-27-imac-with-32gb-kingston-hyperx.html

this is an older model of the memory but the new one is even more in accordance with Apple specification because it's low voltage.

Yes, I will try with 4x4GB modules tomorrow moved directly from a different iMac. I will inform you about the result.

OK so I tried the 4x4GB 1333 modules - doesn't work.

I tried 2x8GB 1333 Apacer modules, 4x2GB Hynix, some additional 4GB, 8GB, etc - all of them working in different iMac.

I even put the 4x8GB hyperX into an older model and... it works like a charm 32GB.

So I think it must be some other problem, not the modules. Any ideas on this?

I would really like to avoid opening the iMac because I have a cracked glass in the corner and probably I will damage it beyond repair...

OK, but the memory HyperX which I have is perfectly fitting the specification: they are 204 pin, they are PC3, they are 12800 and they are SO-DIMM + they are 4 exactly perfectly the same.

Nonetheless probably they are too fast indeed.

If I put a 2x8GB 1333 memory into bay 1&2, the system will work with the additional 2x8GB HyperX 1600 (bay 3&4) but will see only 24GB and only at 1333 speed!

So there IS a probem with the iMac because it works at the nominal specification memory speed ONLY from the first 2 bays. I will buy slower stock 1600 memory with CS11 but I still have doubts if it will work (it doesn't work if I put 4x8GB 1333 modules).

In other words: the max specification late 2012 iMac is barely keeping up with the promised parameters and CS9 memory modules are for sure too much to handle (if you want to have more then 16GB)

I would be grateful if somebody with the same model could specify which exactly modules he uses to have 32GB 1600 Mhz memory. I don't have all producers available in my country, for example OWC.

OK but I also can put 2x8GB and it works - problem starts when I want to put 4x8GB. Look at the specs I posted - 16GB. That's the 2x8GB HyperX 1600 Mhz CS 9 modules.

When I put 2x8GB HyperX 1600Mhz CS 9 modules - it works.

When I put 4 of them - it doesn't.

The only way I managed to put more memory is to put 2x8GB but 1333Mhz and 2x8GB 1600 Mhz - but then I finish with iMac recognizing only 24 GB at 1333 Mhz speed. So the bay nr 4 stays unrecognized and the faster memory runs at the slower speed (matching the first 2 bays memory).

But THATS WRONG. And I wouldn't blame it on the memory modules. For me its a configuration of memory problem which should be addressed by Apple. As you see it's not that common configuration and for most of people 16GB is more then enough. And have you seen an apple support email anywhere? Because the phone support just couldn't help me with the issue (as also the local premium reseller service...).

It also works 16GB at 1333Mhz when I put 2x8GB apacer or, 2x8GB Goodram modules. But for example when I put 4x 4GB 1333Mhz GoodRam modules - it doesn't work. So it's a timing issue between the channels 1&2 and 3&4. That's the EFI problem.

Yes, it's a perfect solution. For Apple.

I have no choice but to replace the memory modules although they meet the specs and DO work in the computer (2 pcs. at least) because Apple will not care to fix the firmware to eliminate the problem. But why would it if it has hundreds of people who will not allow to say a bad word about it?

So thanks for all the help. I am very unhappy with Apple on this subject and that's it.