2017 27" iMac accepts 2666mhz Ram.

[JohnnieBBadde]

This has been possible for a few generations:

I've been using a 2012 non-Retina MBP with Ivy Bridge platform and a few years ago I decided to upgrade to 16 GiB memory. Since there was a special offer I took two Kingston 8 GiB-DDR3-2133 memory modules and also thought that they would just run at Ivy Bridge's default 1600 MHz. But due to "Auto-OC" settings stored in the memory's SPD they also actually ran at 2133 MHz.

This resulted in memory errors that could possibly currupt your data silently. The memory modules themselves were fine but the MBP's logic board wiring or the CPU's overclocked memory controller weren't able to handle the higher frequency properly.

So if you choose to stay with the 2667 MHz memory modules I recommend that you perform intensive memory testing with Passmark's MemTest86 (Free edition), the default amount of test runs is 4 but I would change it to 99 and let it run over-night and only if there are 0 memory errors after at least 6 complete test runs I would start letting the iMac handle data.

PS: A special shout-out to the buttholes from Intel's marketing team that decided to block the use of ECC memory in "consumer-grade" platforms.

 

[princeking]

Ok thanks, I was going to get the base 27' and upgrade the ssd, ram and cpu myself. Yes I know it voids the warranty which I'm not really bothered about. Having seen the price difference between the 4.2 ghz cpu, it works out cheaper to go with the apple upgrade for the cpu. I will eventually swap out the hd for an ssd and upgrade the ssd. Ram is on the way vengeance 2666 32gb.

 

[CaptRB]

I'd say over 90% of the people here keep the original RAM and upgrade to either 24 GB (original 8 GB + additional 16 GB) or 40 GB (original 8 GB + additional 32 GB). And a few do go for 16 GB total.

I'm running 24 GB for example. And yes, with 24 GB, it still gets dual channel performance.

So far I've only seen a couple of users (including yourself) that installed 64 GB. I'd guess it's less than 2% of iMac owners with 64 GB RAM.

Yup. 24 GB appears to be the typical upgrade path.


R.

 

[J.Gallardo]

Crucial RAM runs at the same timings, if you select the RAM using their RAM selector. As do many other RAM modules.

And no, it is not cheaper to get 32 GB RAM and sell the stock RAM than it is to just buy 16 GB RAM and go with 24 GB total.

However, if you really do need 32 GB, then you may as well make it 40 GB, because you're not going to get much money on eBay for the 8 GB of stock RAM.


Yes. It's interesting to hear.

However, for those who need a fair bit of RAM, it's usually better to have 8 GB more RAM than the 1% performance increase that 2666 MHz RAM would provide.

http://www.anandtech.com/show/8959/...-3200-with-gskill-corsair-adata-and-crucial/4

I'd take 40 GB 2400 MHz over 32 GB 2666 MHz any day. 40 GB is 25% more RAM than 32 GB.

I totally agree.
But I remember another thread where this point was discussed, and someone with 40Gb stated that this was the logical way to upgrade ALSO because you could reach 64GB just later, removing original 8Gb & installing another 32pack. Going 40Gb instead of 24 has a (small) point. Of course, if your work is high RAM demanding...
For someone who definitely needs 64Gb, this is big news (where are those pros whose time is gold?), as ALSO, as the thread opener points out, because it can be found cheaper than 2400.
So, is nice to have your very reasonable exposition,
BUT I want to specially appreciate and thank the OP info, as it’s a nice discovery! (New Intel Coffe Lake i7 & i5 offer 2666Mgh RAM support as a novelty... I’ve read prior gen -this- supported up to 2400...here, for example: http://www.tomshardware.com/reviews/intel-coffee-lake-core-i5-8600k-cpu,5264.html )

 

[Ayush0721]

Testing with a 2017 iMac, thought i'd see if it'd take 2666mhz sticks and assumed it would and clock them down to the 2400 standard Apple advertises and sells, instead, it actually runs them at 2666 (reported as 2667mhz in macOS as it likes to round things up)

Thought it might be interesting for some - I didn't run a benchmark on it yet but I will in the future - in the UK currently 2666mhz ram is actually cheaper (the 2400mhz have gone up 30% from retailers since the iMac launched)

I suspect it'll run lower clocked ram easily too (the 2015 model did) and it'll probably run 3000mhz ram, if not at 3000, at 2666mhz no problems. So more options to shop around.

Does iMac 27 inch support more than 16gb 3000mhz ram??

 

[nambuccaheadsau]

The current 27" supports 64GB of 2400Mhz DDR4 SO-DIMM memory.

 

[J.Gallardo]

The current 27" supports 64GB of 2400Mhz DDR4 SO-DIMM memory.

Officially... should we presume.
The Opening Post shows clearly 64GB of 2667Mhz DDR4 SO-DIMM memory is "supported"...
So, you think the screenshots could be fake, or think 2667Mhz could harm something...?
(Of course, guaranty off...)

 

[nambuccaheadsau]

May be supported but will run at 2666MHz?

And as the OP says you will not notice such a small difference, except in the hip pocket nerve replacing the original 2400MHz.

 

[Philip Stancil]

Testing with a 2017 iMac, thought i'd see if it'd take 2666mhz sticks and assumed it would and clock them down to the 2400 standard Apple advertises and sells, instead, it actually runs them at 2666 (reported as 2667mhz in macOS as it likes to round things up)

Thought it might be interesting for some - I didn't run a benchmark on it yet but I will in the future - in the UK currently 2666mhz ram is actually cheaper (the 2400mhz have gone up 30% from retailers since the iMac launched)

I suspect it'll run lower clocked ram easily too (the 2015 model did) and it'll probably run 3000mhz ram, if not at 3000, at 2666mhz no problems. So more options to shop around.

Thank you SO much for posting this! I wasn't relishing the idea of going through the process just to find it wouldn't work.

 

[levmc]

[doublepost=1549979168][/doublepost]

Good to know. I've been running 32 GB of 2133 MHz DDR3 in my Late 2015 iMac and it also runs at native speed, works just fine. Just another reason I'm glad the 27" iMac still has upgradable RAM, and wish Apple would release a new Mac mini with it as well.

I don't recommend mixing, and all of it runs at the lower speed (2400 MHz).

Would 2666 32GB be better or worse than 2400 40GB?

 

[redheeler]

Would 2666 32GB be better or worse than 2400 40GB?

32 GB is plenty for most uses, just go with that unless you have a specific need for more.

 

[levmc]

32 GB is plenty for most uses, just go with that unless you have a specific need for more.

I'm planning on buying 32GB but I'm not sure if I should take out the 2400 8GB and add the 2666 32GB, or leave the 2400 8GB while adding on the 2666 32GB for a total of 2400 40GB.

 

[J.Gallardo]

I'm planning on buying 32GB but I'm not sure if I should take out the 2400 8GB and add the 2666 32GB, or leave the 2400 8GB while adding on the 2666 32GB for a total of 2400 40GB.

I made as you are planning, but all my banks are 2400, so I had no doubt: I'm using 40GB.
If you install all your blades, frequency shown will be 2400, the minimum clock speed. It shouldn't have side-effects other than that, AFAIK, but with these things... I wouldn't take the risk, because I realise I have never reached the top in memory usage; MacOS seems to administre memory, and I believe , for sure, that 32GB would do for me. System seems to know how to waste RAM proportionally, and I think 32GB is a sweet spot, and my mac rarely (if ever) has used more than 28 or so...
I would go the safest way; in my opinion (and with my needs) your system won't make use of those extra 8GB and your RAM will be slightly faster (someone pointed that shown frequency perhaps isn't real).

 

[yurkennis]

I'm planning on buying 32GB but I'm not sure if I should take out the 2400 8GB and add the 2666 32GB, or leave the 2400 8GB while adding on the 2666 32GB for a total of 2400 40GB.

@levmc, have you managed to add a single 32GB 2666MHz stick to pre-installed 8GB 2400 MHz on 2017 iMac 27"? If so, what CPU is in your iMac? Did the upgraded RAM meet your expectation in performance and stability?

 

[Aiwi]

I've now ran some benchmarks with the following RAM configurations:

• 2400MHz 2x4GB Stock Apple
  • CL17/18, theoretical latency: 14.2-15ns
• 2666MHz 2x16GB Kingston HyperX
  • CL15, theoretical latency: 11.3ns
• 2400MHz 2x8GB Apple + 2x16GB Kingston
  • All sticks auto down-clocked to 2400MHz and CL17/18, theoretical latency: 14.2-15ns

Geekbench 5 score was:

• Singe Core: 905 - Multi Core: 3275 (8GB 2400MHz Apple RAM)
• Singe Core: 971 - Multi Core: 3536 (32GB 2666MHz Kingston HyperX RAM) +7-8%
• Singe Core: 971 - Multi Core: 3673 (40GB 2400MHz Apple+Kingston RAM) +7-12%

The conclusion has to be that Geekbench 5 (and overall performance) goes up with more RAM. The theoretical reduced latency does not translate to greater Geekbench scores. I did notice a couple of category benefits for the 2666MHz RAM, like Machine Learning, though.

I ended up having the two 2666MHz sticks only. I want to have the best theoretical performance, regardless of what Geekbench tells me...

 

[h4lp m3]

I'd say over 90% of the people here keep the original RAM

Hell, I don't. I sell it on eBay to offset the cost of a RAM upgrade.

 

[mitjam]

I made as you are planning, but all my banks are 2400, so I had no doubt: I'm using 40GB.
If you install all your blades, frequency shown will be 2400, the minimum clock speed. It shouldn't have side-effects other than that, AFAIK, but with these things... I wouldn't take the risk, because I realise I have never reached the top in memory usage; MacOS seems to administre memory, and I believe , for sure, that 32GB would do for me. System seems to know how to waste RAM proportionally, and I think 32GB is a sweet spot, and my mac rarely (if ever) has used more than 28 or so...
I would go the safest way; in my opinion (and with my needs) your system won't make use of those extra 8GB and your RAM will be slightly faster (someone pointed that shown frequency perhaps isn't real).
View attachment 821625

Hi J.Galardo.
Do I understand you correctly, that you mixed stock 2400 8GB with 2666 32GB? And it worked? Albeit on 2400 altogether.
Which vendor did you use? Crucial, ...?

I would like to add RAM, and it is easier to get 2666 than 2400 nowadays (and even cheaper).

 

[J.Gallardo]

Hi J.Galardo.
Do I understand you correctly, that you mixed stock 2400 8GB with 2666 32GB? And it worked? Albeit on 2400 altogether.
Which vendor did you use? Crucial, ...?

I would like to add RAM, and it is easier to get 2666 than 2400 nowadays (and even cheaper).

No. I was answering someone asking about mixing frequencies. I’d heard it works throttling to lower one, and I recommended NOT taking the risk, and sacrifice smaller and lower frequency memory blades.
I upgraded long ago, and went up to 40GB, all 2400. If I were to upgrade now, I would get 32GB 2666, BUT would discard memory that came with Mac. Better 32 at full speed than slower 40gb. Once 32 gb are reached, bigger size doesn’t make a difference. IMHO.

 

[mitjam]

No. I was answering someone asking about mixing frequencies. I’d heard it works throttling to lower one, and I recommended NOT taking the risk, and sacrifice smaller and lower frequency memory blades.
I upgraded long ago, and went up to 40GB, all 2400. If I were to upgrade now, I would get 32GB 2666, BUT would discard memory that came with Mac. Better 32 at full speed than slower 40gb. Once 32 gb are reached, bigger size doesn’t make a difference. IMHO.

Thank you for your answer.
I have 24GB now. My thoughts were mixing 2x8 2400 with 2x16 2666. I have to ditch 16GB actually (+8GB of stock one anyway).
Abandoning 16GB does not seem negligeble to me...
Has anyone tested a mix of 2400 and 2666?

 

[mitjam]

I just upgraded RAM in iMac 27" 2017 with 2 x 16GB sticks, Crucial 2 x CT16G4SFRA266 (not specifically certified for Mac - as someone mentioned, "for Mac" should have the same specs, just RAM built in materials corresponds Apple standards).

RAM works at full speed of 2667 MHz in iMac 2017.

Then I also added older RAM sticks, 2 x 8GB 2400 Crucial CT8G4S24AM (for Mac).
Newer RAM is down-clocked to 2400. But there is 48 GB of RAM inside now.
I inserted 2667 RAM in 2nd and 4th slot (from bottom up)to DIMM1 and not DIMM0 slots, as someone suggested. Maybe it is better that 2400 RAM is detected first in DIMM0 slots.

Latency of 2667 RAM is mathematicaly 11% lower than 2400. However, overall performance of memory when running at 48GB@2400 instead of 32GB@2667 is very similar according to Geekbench 4 test.

If you never consume more than 32GB, than 32GB @2667 is probably better option. At least latency is 11% lower.
However, when you overcome 32GB limit, and computer starts to swap to disk, than slightly lower latency means nothing compared to swapping cost to my opinion!

Geekbench 4

32GB @2667MHz

• Single-Core Score: 5703
• Multi-Core Score: 19877
• Single Core:
  • Memory Copy: 5345, 14.8 GB/sec
  • Memory Latency: 7142, 60.6 ns
  • Memory Bandwidth: 4893, 26.1 GB/sec

48GB @2400MHz

• Single-Core Score: 5711
• Multi-Core Score: 19943
• Single Core:
  • Memory Copy: 5405, 15.0 GB/sec
  • Memory Latency: 6577, 65.8 ns
  • Memory Bandwidth: 4898, 26.2 GB/sec

(I just made one test of each RAM combination. Probably results would vary if more test runs would be made!)

 

[Ant.honey]

I just upgraded RAM in iMac 27" 2017 with 2 x 16GB sticks, Crucial 2 x CT16G4SFRA266 (not specifically certified for Mac - as someone mentioned, "for Mac" should have the same specs, just RAM built in materials corresponds Apple standards).
View attachment 1767537
RAM works at full speed of 2667 MHz in iMac 2017.
View attachment 1767540

Then I also added older RAM sticks, 2 x 8GB 2400 Crucial CT8G4S24AM (for Mac).
Newer RAM is down-clocked to 2400. But there is 48 GB of RAM inside now.
I inserted 2667 RAM in 2nd and 4th slot (from bottom up)to DIMM1 and not DIMM0 slots, as someone suggested. Maybe it is better that 2400 RAM is detected first in DIMM0 slots.
View attachment 1767541

Latency of 2667 RAM is mathematicaly 11% lower than 2400. However, overall performance of memory when running at 48GB@2400 instead of 32GB@2667 is very similar according to Geekbench 4 test.

If you never consume more than 32GB, than 32GB @2667 is probably better option. At least latency is 11% lower.
However, when you overcome 32GB limit, and computer starts to swap to disk, than slightly lower latency means nothing compared to swapping cost to my opinion!

Geekbench 4

32GB @2667MHz

• Single-Core Score: 5703
• Multi-Core Score: 19877
• Single Core:
  • Memory Copy: 5345, 14.8 GB/sec
  • Memory Latency: 7142, 60.6 ns
  • Memory Bandwidth: 4893, 26.1 GB/sec

48GB @2400MHz

• Single-Core Score: 5711
• Multi-Core Score: 19943
• Single Core:
  • Memory Copy: 5405, 15.0 GB/sec
  • Memory Latency: 6577, 65.8 ns
  • Memory Bandwidth: 4898, 26.2 GB/sec

(I just made one test of each RAM combination. Probably results would vary if more test runs would be made!)

So, I am in the same boat as you. Would like to keep the 2x8 2400 that I have and add the 2x16 2666mhz (32). Are you still happy with that setup? I am constantly swapping to disk with large files.

 

[mitjam]

So, I am in the same boat as you. Would like to keep the 2x8 2400 that I have and add the 2x16 2666mhz (32). Are you still happy with that setup? I am constantly swapping to disk with large files.

It is Ok for me. No swapping to disk any more ;-) Comp is less laggy now when I have lots of browser webpages open.
Before upgrade there was 10GB+ of swap space used. Now swap is empty.

After upgrade you will notice that there is still aprox. half of RAM marked as inactive. Arround 20GB in my case.
If I do “ sudo purge” in Terminal, the situation does not change much.

 

[Pufflesthemallow]

This question is mostly on topic.

Does the 21.5" version of the OP accept 2666mhz RAM? I've looked around online quite a bit and only found references to the 27" version. Not even posts about how the 21.5" doesn't take it. So, anyone able to shed some light on it?