• Crucial 16gb Ddr4 2400mhz Sodimm Memory Module Kit For Mac (2 X 16gb)
• Crucial 16gb Ddr4 2400mhz Sodimm Memory Module Kit For Mac (2 Points)
• Crucial 16gb Ddr4 2400mhz Sodimm Memory Module Kit For Mac

Click to expand.(to the person I replied to in the first quote, don't read this part or it'll confuse you more ) I have no idea how to reconcile your experiment with it, but people wanting to know how to do dual-channel layout should check out: That has all the proper layouts for dual channel. I don't have my 27' yet-still in processing-but the teardowns show Apple shipping in the 0-4-0-4 configuration as seen top-down when on the stand. That corresponds exactly with the Intel diagram for 2-DIMM/dual-channel, so I'm assuming top-down in the diagram and top-down on the iMac correspond. They're supposed to be filled in 3142 order, in that orientation. So in your trials, assuming that's correct, 8-4-0-4 (or 4-0-4-8 counted from the bottom, as it seems you have) should have been canonical 3-DIMM/dual-channel; 0-4-8-4/4-8-4-0 should've worked if the chips were close enough in timing and the population order within a channel isn't significant (not sure on this one for iMac but it's usually not); and 0-8-4-4/4-4-8-0 should have thrown it into single channel/asymmetric mode. Of course, that doesn't match your results. FWIW, benchmarks can also have some variability (test professional here) and the Crucial RAM might also be faster than the Hynix RAM the iMac ships with.

If GeekBench doesn't exercise all of the RAM capacity, maybe 8GB in single-channel would beat 4GB in dual, with your chips. Reversing the population order would show that difference if it's there, though I find that pretty unlikely and the difference between 0-4-0-4 and 0-8-4-4 was big enough to look non-specious. One possibility I see is that your RAM timings aren't quite matched enough so that 0-4-8-4 threw it into degraded dual-channel setup. Another is that Apple is absolutely wacky and didn't interleave their channels in the slot layout, but that seems unlikely since they ship with an interleaved setup.

Another still is that population order is significant after all. If you're ever feeling really generous with your time, it'd be interesting to see if 8-4-0-4 performs better. It'd also be interesting to know how System Information/Hardware/Memory is reporting the populated BANK/DIMM numbers and the speed it says everything is running at.

Maybe 0-4-8-4 downclocked you to 2133Mhz, for example. This seems to be the same part as this one at Amazon.com: Because you are outside the US and Amazon has an Australian store, Georiot may redirect you. You can copy and paste the URL. Anyway, it looks like it will work just fine and there are comments in the reviews from others who have installed it in the 2017 iMac already. Micron themselves state right in the Q&A that the RAM should work fine in the 2017 iMac but that they recommend the 'for Apple' part because they haven't tested it yet. Meanwhile, lots of other users have and (I'll say it again) as long as you get good quality (Crucial, Hynix, Samsung, etc) RAM at the proper specs you should have no issues at all.

Click to expand.The problem being (as I think you were the one who pointed out) that some RAM a la HyperX can't maintain its rated speed at the higher latency, which in turns drags the speed of the Apple RAM down to its level if it falls back to 2133Mhz. If the DIMM is rated at 2400Mhz at CL17 all is well. 2400Mhz at anything lower can be a bit of a crapshoot if you're mixing with stock, though you're right on that I wouldn't normally concern myself with CL16 vs. I'd watch out heavily for 'enthusiast' RAM with low CLs though. Click to expand.I won't argue the point on latency-I think I was probably incorrect regarding relationship between speed and CAS-but I think whoever read the HyperX spec sheet was pretty mistaken on it being 'overclocked.'

I think they were homing in on 'Note: HyperX DDR4 PnP memory will run in most DDR4 systems up to the speed allowed by the manufacturer's system BIOS. PnP cannot increase the system memory speed faster than is allowed by the manufacturer's BIOS. Memory overclocking is locked at 2133MHz on all mobile processors except Core i5 and i7 quad core processors with a TDP of 45W or greater.' What it is, is PnP.

Crucial 16gb Ddr4 2400mhz Sodimm Memory Module Kit For Mac (2 X 16gb)

That means instead of having to manually go enable high-speed mode in your BIOS (XMP), the BIOS should configure itself to run the RAM at the max speed (and most aggressive timings) allowed by default. The disclaimer is saying if your BIOS is locked at 2133Mhz (as opposed to just defaulting to it), there's no way to make the RAM go faster via PnP. Either way, the RAM is still rated at 2400Mhz. The overclocking part refers to the motherboard's handling of the RAM, not the RAM itself. For DDR4, most mobos only support up to 2133Mhz by default and running any 2400Mhz RAM is considered to be overclocking.

HyperX is generally marketed to PC gamers who want to do that as an easier solution than manual configuration of XMP. My guess is it's not playing nice with EFI, since EFI is more than a little different than standard PC BIOSes. It's deciding under some circumstances to only run at standard DDR4 speed as if the 2133Mhz support wasn't there. Maybe there's a handshaking thing that's supposed to happen and doesn't if the stock RAM is also installed.

If someone is stuck with the HyperX SODIMMs they might try swapping slots between it and the stock RAM to see if that helps. Might be a case of which is in the first slot. Click to expand.Yes, and the PnP, which, as you mentioned, automatically ramps the RAM up to the system speed is the problem here, not the CL. As I also previously mentioned there should be no problems if you're using the Kingston on its own and they do make good RAM.

If you want to use RAM in addition to the Apple stock RAM, however, you should avoid the HyperX or any other overclocking memory and get actual 2400MHz RAM with that speed hard coded in the SPD like Crucial's many fine PC4-19200 offerings. I think we actually agree here. On a another note, I finally got around to running Memtest86+ (From a USB flash boot drive) with 2x16GB of Crucial Ballistix Sport (which the compatibility tool on the Crucial site declares as 'incompatible') added to 8GB of Apple RAM for 40GB. 4 passes so far, 4 solid hours and zero errors and the ambient temperature in the room is 35C right now! The fans on this machine aren't even running fast. I'm going to declare the Ballistix as a solid recommendation.

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Click to expand.At least the current gen iMac has its hatch at the back, so it's accessible even when the Mac is upright on its stand. I remember my 20' iMac G5 ten years ago had screws at the bottom air intake /speaker grills, unit had to be unscrewed face down, and then the whole back case slided off to access the internals. I don't think I was too scared off by it not booting up, AppleCare had me covered anyway, but the thought of having to pack and send back the whole thing was indeed not nice to have lol. I've got the exact same issue. And I've figured out why and how to fix it. 1) To fix it, remove the stock ram, put your HyperX in slot 1 and 3 only, run as 32 gb. You will get 2400 MHz.

2) I've done a number of test and found running with HyperX 32gb only has the highest performance, infact, my iMAC has the highest score for 2017 model on Geekbench, better than stock 64gb. 3) The reason is HyperX has faster CL, only 14, where stock Apple ram has 17, therefor when you mix different CL speed, HyperX will slow down to 2133 MHz. Actually, it raised factory RAM's CL to 14, however, factory ram will slow to 2133 when CL@14 and force hyperx to 2133 as well. (Please correct me if I'm wrong) 4) If you want to run 4 rams, then ditch the Apple ram and get another set of 32gb Hyperx, you'll have 64GB and it will run at 2400 MHz. 5) I've done many test and 32GB HyperX alone is almost 10% faster than 40GB of mix factory RAM and Hyper X. 6) On my machine, if I leave factory ram in slot 1,3 and HyperX in 2,4, the iMac would not boot up, fan is working but black screen, waited 2 minutes. It does work if I put Hyperx in 1,3 and factory in 2,4.

But will only run at 2133 MHz and much worse Geekbench scores. Conclusion: Only run the same RAM across all slots. Remove your stock ram and run it with 32GB only. Or buy 2 more HyperX if you want 64gb.

And HyperX is damn amazing. I think only people with 64GB HyperX can beat my Geekbench score. If GeekBench doesn't exercise all of the RAM capacity, maybe 8GB in single-channel would beat 4GB in dual, with your chips.

Reversing the population order would show that difference if it's there, though I find that pretty unlikely and the difference between 0-4-0-4 and 0-8-4-4 was big enough to look non-specious. One possibility I see is that your RAM timings aren't quite matched enough so that 0-4-8-4 threw it into degraded dual-channel setup. Another is that Apple is absolutely wacky and didn't interleave their channels in the slot layout, but that seems unlikely since they ship with an interleaved setup.

Crucial 16gb Ddr4 2400mhz Sodimm Memory Module Kit For Mac (2 Points)

Another still is that population order is significant after all. If you're ever feeling really generous with your time, it'd be interesting to see if 8-4-0-4 performs better. It'd also be interesting to know how System Information/Hardware/Memory is reporting the populated BANK/DIMM numbers and the speed it says everything is running at. Maybe 0-4-8-4 downclocked you to 2133Mhz, for example. Click to expand.Well, you can see how it's being reported, which banks are populated and how, and you can see that it's all being reported as 2400MHz. TBH, I've gone as far as I'm going with this. I've always understood that multi-channel works with equal quantities of similarly specced RAM in each channel.

Crucial 16gb Ddr4 2400mhz Sodimm Memory Module Kit For Mac

The easy way to achieve this in a dual channel machine is to install paired DIMMS across the channels, but it's not the only way. I'm satisfied that I've got 16GB installed cheaply and working efficiently in dual-channel mode. If I need any more RAM in the future, I'll add another stick of the same Crucial RAM, rearranging it to 4-8-4-8.

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