Late 2015 27 iMac 5k RAM spec

Hopefully that brand will work for you as it does not have a very good track record on these forums. Personally, I do not let anything Kingston near my Macs any longer.

Hi Joe Siegler - is your iMac late 2015 a i7 or i5?

I bought two paris of CT2KIT102464BF186D, from different vendors and it under clock the ram to 1600 Mhz. I tried each pair individually and then together, results were same.

Reading on Amazon it seems the i7 models don't under clock this Ram.

I was thinking of returning but now am deciding why bother, I hope the speed difference between 1600 and 1866 is not minor. I would have preferred the 1866 speed since that is what I paid.

Hi Pinkxter, I got the same kit as you from Ebay and its under clocked the ram to 1600 MHz. I have contacted the seller and asked him whats going on but no replies yet. Did you manage to sort this one out?

Hi realistsun, it is not the sellers fault. Contact crucial, there is a thread on crucial's forums on same subject, they say to contact them via support.

Was your i5 or i7 iMac?

Hi guys,

Like you, I just bought this awesome iMac 25 5K with the M395X 4Go graphic card with minimal RAM : 2x4Go.

I also want now to get a bunch of RAM 😀

⚠⚠⚠

I'm reading all your posts and there is an information you seem to miss :

The DDR CAS Latency (CL).

⚠⚠⚠

CAS Latency is the number of cycle to access the data. MHz is the number of cycles per seconds.

Dividing cycles by cycles per seconds, you get seconds : The time to access data.

1866MHz

Be careful with cheap model with CAS Latency (CL) 13 :

This means you have an actual time for Memory access of 13/1866 = 0,7 centi-nanoseconds.

There is a big difference with CAL Latency 10 : 10/1866 = 0.54 centi-nanoseconds.

But this is more expensive.

1600MHz

Even a 1600MHz with CL10 is better : 10/1600 = 0.63 centi-nanoseconds.

And a 1600MHz with CL9 is better than the 1866CL10 : 9/1600 = 0.48 centi-nanoseconds.

Does that makes sence ?

Then I guess I found a nice model : http://www.ldlc-pro.com/fiche/PB00170724.html

(Sorry for french link, check the reference)

⚠⚠⚠ Careful again with multiple sets of RAM, the minimal CL is used : DONT mix Super Low CL with a normal CL : Useless !

Sorry I can't Edit my first POST.

There is a mistake I made with the actual RAM frequency which is always Half the faced one.

1866MHz (Actual frequency is 933Mhz)

Be careful with cheap model with CAS Latency (CL) 13 :

This means you have an actual time for Memory access of 13/933 = 1.39 centi-nanoseconds.

There is a big difference with CAL Latency 10 : 10/933 = 1.07 centi-nanoseconds.

But this is more expensive.

1600MHz (Actual frequency is 800Mhz)

Even a 1600MHz with CL10 is better : 10/800 = 1.25 centi-nanoseconds.

And a 1600MHz with CL9 is better than the 1866CL10 : 9/800 = 1.13 centi-nanoseconds.

1600MHzCL9 is 5% faster than 1866MHzCL10 (instead of 11% in my previous post, which can make a difference comparing prices)

that being said there is more bandwidth available on a higher MHz RAM.

Things like video editing benefit more from more bandwidth than lower cas latency.

Again, another mistake in the conclusion, it is the opposite :

1866MHzCL10 is 5% faster than 1600MHzCL9 and surprisingly, it it 5% more expensive 😉

I did not see if follow up post from spf57, about the ram from OWC. I recently bought the same two 16 gig chips, installed them in all different slots and combinations, but without fail I could not go more than a day or sometimes an hour, without my screen going dark, and my computer logging me out. Every time I took them out of the computer, I did not have this problem. I assumed wonder one or both were defective, and sent them back for a replacement, but the new ones they sent me exhibit the exact same behavior.

When I talk to Apple, they of course told me that they can't guarantee third-party RAM, but I could bring my 27 inch iMac to my local Apple Store and they could test it with different brand of RAM chips. Have held off on that for now, and I'm also trying to deal with OWC to figure out if the problem is just my RAM, or all their branded chips in general. If anyone has any experience, good or bad, using OWC 16 GB chips in there 5K iMac, it would be great hear from them.

Hi raripps, just want to let you know that I'm using the 16 gig chips from OWC with no problems at all. Since they sent you a different set and the computer is still exhibiting that strange behavior then it has to be the computer. Why don't you take out the 16 gig chips and put in the original 8 that came with the system? You'll know after a while if its the computer acting up.

This is chip I'm using;

OWC 16 GIG SET.

Hope this helps.

Hi spf57, Sorry for the late response. I never saw your question and did not receive an alert about it. I only saw it after receiving an alert for a similar question by member raripps. I left him a detailed answer which answers your question as well.

I do have one question for you, did you migrate all of your files and system form the old computer? That could be the conflict if so. I did a fresh clean install and re-installed all of the software. Very time consuming but no problems as of yet.

Hope this helps.

Another question I have for you, did you migrate all of your files and system from the old computer? That could be the conflict if so. I did a fresh clean install and re-installed all of the software. Very time consuming but no problems as of yet.

I have run the computer without the first set of 16 gig chips and the second. Whenever the original factor RAM is installed, this problem does not occur. Not even once. As soon as I put in the larger 16 gig chips I have the problem. So whatever it is, it's a problem with that RAM in this computer.

I have worked with Apple to check the computer but it never shows a problem. I heard from OWC today who suggested that I run rember to test the ram. So at some point I'll take out the good ram, putting in the bad RAM and run the utility and see if it shows anything to be problematic.

Here are a few things you can try. Click the links for the information.

Make sure the ram is seated properly. Push it down a little harder but be careful. Do this first before everything else. Keep me posted..

ZAP THE P-RAM

HARDWARE TEST

RESET SMC

OWC 16 GIG MODULES

OWC INFO ON TROUBLE SHOOTING

Have tried all of these things either on my own, or with Apple- hardware tests have shown no problems, and I just ran a ram test four times. Two out of the four times it stopped with the problems, I have sent the results to OWC, and I'm awaiting their reply.

Thanks for the suggestions though.

To be continued...

Great, so it appears it is definitely the ram. Did they send you a new memory kit before you you returned yours or after? You don't want them sending you the same ram back and saying it's a new chip set.