Late 2015 27 iMac 5k RAM spec

I can confirm that the Crucial Ballistix RAM I linked to on Amazon at http://www.amazon.com/gp/product/B00DSGLMSM (Crucial Ballistix Sport 16GB Kit (8GBx2) DDR3 1866 (PC3-14900) 204-Pin SODIMM Memory BLS2K8G3N18AES4 / BLS2C8G3N18AES4) seems to work perfectly in my late 2015 5K iMac. I put them each into the original spots where the pre-installed Apple RAM was, then the Apple RAM in the alternate slots.

Thus:

==== iMac monitor ====

Apple RAM

Ballistix 8 GB

Apple RAM

Ballistix 8 GB

=== iMac Foot ======

Thus, you can see the Ballistix RAM is listing as the same 1867 MHz as the Apple 4GB modules.

I suspect the Crucial rep advised against the Ballistix is that is hasn't been specifically tested on the new iMac and I'd bet they routinely only recommend actual tested modules.

I'm comfortable with this small risk since the spec matches other than the single Mhz (1866 vs 1867) but as another poster mentions, this is likely just Apple's rounding.

Thanks Steve. This is reassuring. How long have you been running your new iMac in this configuration. Btw, here's what Crucial Support wrote to me: "Most Ballistix modules do not have typical memory latencies and voltages that Apple systems use and unfortunately Apple systems can be a bit picky. It's possible the Ballistix parts will work, but we cannot guarantee it."

Interesting. Sounds like a well thought out reply.

I only just installed the Ballistix RAM last night and the system has been running 24h since, as I am transferring over a huge 2.5 TB home folder. So far the system seems rock solid, with no crashes or glitches, or errors. There's plenty of IO operations happening right now via USB3 and Thunderbolt as well as WiFi.

If I get instability or random errors, I'll post back. Thinking about buying Techtool pro 8 and seeing if its memory test is useful or not.

Hi everyone i'm waiting for the arrive of Imac but i've already bought these http://www.amazon.it/gp/product/B00VMCUBK4?psc=1&redirect=true&ref_=ox_sc_act_ti tle_2&smid=A11IL2PNWYJU7H. On kingston site this ram is marked like compatible with Imac 27 5k late 2015🙂

Well, I certainly hope that Kingston has tested these on Macs - I do not buy that brand any longer as it did not play well with my Macs. I only buy from vendors who specifically test their RAM on Macs: OWC (macsales.com) or Crucial.

FWIW, I purchased this RAM at B&H (http://www.bhphotovideo.com/c/product/1121919-REG/crucial_bls2k8g3n18aes4_16gb_2 04pin_sodimm_ddr3.htmlbut have not installed it yet. After reading this thread I chatted with the B&H Apple specialist. I quoted to him the Crucial statement "Most Ballistix modules do not have typical memory latencies and voltages that Apple systems use and unfortunately Apple systems can be a bit picky. It's possible the Ballistix parts will work, but we cannot guarantee it."

He responded:

James B: I am aware of that, however we have not had any customer complaints about this RAM in the new iMac's.

How were the results? compatible? did you kept the original apple RAM in the system? Im looking in doing the same for the Crucial found on Amazon

I confirm that these work perfectly http://www.amazon.it/gp/product/B00VMCUBK4?psc=1&redirect=true&ref_=ox_sc_act_ti tle_2&smid=A11IL2PNWYJU7H and are read 1867 mhz

Have had no issues with this RAM. It's reported as 1867MHz. I ordered my iMac with 16GB and added the module to the two open slots. Crucial Ballistix Sport 16 GB (2 x 8 GB) DDR3 PC3-14900 Memory Module MFR # BLS2K8G3N18AES4

If I had it to do over again I would have bought the iMac with 8GB, tossed those and put this RAM in. Would have saved $112.

I installed Crucial Ballistix Sport 16 GB in addition to the existing 8GB and everything so far is running flawlessly.

Did you have any issues with the 16gb sticks from OWC? I installed mine (16gb x 2 from OWC) and started getting panic reports and restarts due to errors. Took out the memory and now no issues. I'm debating on whether I just get new 16gb to get up to 40gb RAM or go down to 8gb for better potential for not having that issue. However would love to have 40gb of RAM.

I bought the Crucial CT2KIT102464BF186D kit but it underclocked my Ram to 1600 while the existing iMac 2 x 4GB modules are in the system.

Not sure why this happened, the RAM is advertised as 1866 Mhz from Crucial

FWIW, the 64GB kit is now $697.99

I successfully installed 2133 MHZ memory in my late-2015 iMac.

Kingston Hyper Impact HX321LS11IB2K2/16.

I choose to remove the two factory 4GB 1866 MHz modules and use two 8GB 2133 MHz modules instead.

2133 MHz? Why? it won't run any faster.

nevermind, I looked up the specs. The modules run at either 1600, 1866 or 2133 depending on the PnP JEDEC timing. Which in your case is 1866Mhz.: