Problem with 16GB on 2010 iMac 27" i5 & i7.

Thanks mysys,
looks like you are right after all. But I have some questions. What type of ram did you use, transcend or strontium?
I am a bit confused with the banks and slots. Exactly where did you put the ram? If you put the iMac on its screen and open the ram compartment should I put the 2 x 4 G OWC ram in the upper slots and the 1 x 4 G OWC and the 1 x 2 G Apple ram in the lower slots? Or the other way around?
Or does it not matter?
If it works it is anyhow 2 G more in use.

peter willem

Upgraded mine to 16GB.. no problem so far.

Memory was bought from OWC.. Samsung Factory Original







Message was edited by: august77

With the 14 GB set up you have unmatched RAM. The downside is that there is a theoretical speed penalty. Some believe that any performance hit due to mismatched RAM is compensated by the increase in performance of the extra RAM though.

Here is one source. They site 3% improvement with matched pairs.
http://guides.macrumors.com/MatchedRAM_on_IntelMacs

But I agree with you - this could be an unverified legend. You should check benchmarks with 12 GB, 14 GB and 16 GB. It would be most informative.

I'm experiencing the same annoying issue with an iMac Corei7 but with 1066MHz soDIMM modules.

The system was able to run with 12GB RAM (2x2GB and 2x4GB). I decided to update the memory to 16GB. And the system doesn't start. But what's strange is that the system now have problem with 12GB as well!

I tried different combos:

2x4GB hynix modules + 2x2GB hynix (doesn't work or start randomly, once the system run, no problems at all)
4x4GB hynix modules (doesn't work or start randomly, once the system run, no problems at all)
2x4GB Transcend CL7 OMD22 D9LGK (it works)
2x4GB Transcend CL7 OMD22 D9LGK + 2x2GB Samsung CL7 (doesn't work or start randomly, once the system run, no problems at all)

The first configuration, before the 4x4GB update was 2x4GB hynix modules + 2x2GB hynix

Since I won't be able to use the16G OWC ram for a while, I am interested in this matter. Presently I am running 12 Gig. 2 x 4 G OWC and 2 x 2 Apple ram. Works good.
Should I replace one of the apple ram with one OWC ram in the lower slots in order to get more performance? Or will that have the opposite effect?
see this thread, though it concerns an end 2009 type iMac.
http://discussions.apple.com/thread.jspa?threadID=2308302&tstart=0


peterwillem

Here is an other article, although it concerns an other mac, the theory is the same.
http://eshop.macsales.com/Reviews/Framework.cfm?page=/Benchmarks/Core2RAMbenchorig.html

.
Funny that it is written by OWC.

peterwillem

G'day everyone,

I've had my iMac for about two weeks and got this problem as well, glad to find a solution, sad to see the problem in the first place ;-(

I worked as an apple tech a few years ago and saw a similar problem. It took me five weeks of testing to discover that the ram was faulty, the machine always failed while no one was watching, or didn't fail at all. One day I just happened to be watching the ram test when it shut down. Ran a PC test on the ram and confirmed the problem. So when I first saw this happen my immediate thoughts were ram.

I too have OWC ram, and have now changed my configuration to the suggestion posted here. It's a shame that I can't have my 16Gig of ram, but then I'm not sure if I would ever use that much anyway.

I hope Apple are working on a firmware update.

By the way I upgraded from a PowerMac G5 1.6Ghz with 2Gb of ram so I'm lovin' it 😉

Michael

What a thread! I just stumbled across this, and finding this thread would have saved me a considerable amount of time. I only found it by putting in my model number. I thought I'd be safe buying a couple months down the road, after I could see what the issues were.

Unlike your reports, I can consistently trigger a complete and sudden power off by opening a file in Photoshop.

I have iMac Model iMac11,3 Intel Core i7.

I purchased 16GB 1333 MHz DDR3 RAM from OWC with Micron chips. I used memtest and tested each individual module, by plugging them in one by one. I ran the test once, but each module checked out. I had to do this, because memtest will not lock memory above 4GB or something. I then ran Rember in OSx 64-bit mode to test the memory. No errors there, but you can only test what you are not using in the OS, applications, drivers, etc.

I can consistently reproduce the problem with 4x4GB modules. If I take one out, it works. If I replace it with my Apple 2GB, it works.

I just got back from the Apple Store. They were going to replace my machine on the spot, but they did not have one available. They did allow me to try it with Apple RAM. The machine did not crash with the Apple RAM, but this test appears to be inconclusive, as others do not exhibit problems right away with new RAM. I did not see what chipset their RAM was, as it had a big sticker across it.

I'm unwilling to spend $2500 + extra RAM on a machine and not be able to upgrade to 16GB. Or, use part of it for years and then spend for 16GB again. Sorry.

I've just been through this thread, as well as the other two or three referenced. Is this the consensus so far for those shopping for RAM?
4x4 = 16GB Apple RAM (Micron chipset, possibly others) works sometimes
4x4 = 16GB Transcend Hynix chipsets work
4x4 = 16GB Transcend Micron chipsets work
4x4 = 16GB Samsung Factory Original chipsets work

All others have failed numerous times, unless combined in ways that result in less than 16GB total.

FWIW I upgraded to 16gb on my new iMac from OWC as well..was thinking it was RAM but after watching the logs noticed something peculiar...switching from Safari to Chrome has cured my intermittent crashes.

Don't recommend the newest Safari.