iMac RAM speed not displayed accurately

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Level 1

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iMac RAM speed not displayed accurately

Hello.

I just got a 2020 iMac, and was planning on upgrading the RAM myself, but the clock speed isnt being displayed accurately. When it arrived with the Apple Ram(8GB), under "about my Mac", it displayed the ram as 2133MHz, which was different from the advertised 2667MHz. Furthermore, I also bought 32GB of additional "3200MT/s" RAM from here: https://www.amazon.com/gp/product/B08C4X9VR5/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

I took out the 8GB of RAM that came with apple, since I know that would downclock my new RAM. Now, however, Apple "about my Mac" displays my new RAM as 2667MHz, while I was expecting 3200MHz.

I worry that my RAM clock speed is not running at its full potential, and I would like it to for X-Plane 11(for the frame rate). I read somewhere that an upgrade from 2667MHz to 3200MHz would increase FPS by about 30%, but I barely noticed an FPS increase if any.

Am I missing something here? Is the "3200MT/s" RAM supposed to show as 2667, and the 2667 show as 2113? Why is my iMac displaying them wrong?

I read somewhere that the new 2020 iMac was compatible with 3200MHz RAM, as seen here: https://www.reddit.com/r/mac/comments/i5i5js/the_new_2020_imac_has_3200mhz_memory_support/

Any insight would be appreciated

iMac 27″, macOS 10.15

Posted on Oct 2, 2020 10:51 PM

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Answer 1

rkaufmann87

Level 10

140,880 points

Oct 6, 2020 7:11 PM in response to DanieIR1

Did you install the original 8 GBs of Apple supplied RAM in slots 1 & 2 and the upgraded RAM in slots 3 and 4? That is critical!!!!!!!!!!!!!!!! If you do that with the 2666 RAM it should read 2666 speed. If you don't do EXACTLY as I stated you will get 2133 speeds.

Slot 1 is the top slot
Slot 2 is the next slot down,
Slot 3 is below slot 2
You can likely figure out which is slot 4

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Answer 2

DanieIR1 Author

Level 1

10 points

Oct 6, 2020 10:02 PM in response to rkaufmann87

I was not arguing? I was merely asking why your approach makes sense, since it contradicts what I've heard from other sources... it seems only natural to ask if something seems contradictory.

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Answer 3

Oct 7, 2020 6:40 AM in response to DanieIR1

your own screenshot should illustrate your issue.

it's best to leave the apple ram in slots 2 and 4 and add the aftermarket ram into slots 1 and 3. that's what they mean by "install ram in pairs". there's a reason apple puts the stock ram into those positions in the first place. and No, your mac is not compatible with 3200MHz ram. i would recommend getting the correct ram from OWC. you will find the ram you need here.

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Answer 4

rkaufmann87

Level 10

140,880 points

Oct 2, 2020 11:20 PM in response to DanieIR1

My picture shows the slots the RAM should be installed in, that's why I included it. The stock RAM should be in slots 1 & 2 and your upgraded RAM in slots 3 & 4. Why run 32GB of RAM when you can have 40GB, you already have the 8GB of RAM the computer shipped with just add that to the upgraded RAM.

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Answer 5

DanieIR1 Author

Level 1

10 points

Oct 2, 2020 11:34 PM in response to rkaufmann87

That's what I thought too, but the RAM that I bought has a higher clock speed than the stock 8GB. Supposedly, if you have RAM of two different clock speeds, the one with the higher speed down clocks to the one with the lower speed.

I actually tried what you did, but my 3200MT/s RAM went down even more, down to 2133 now. How is your ram clock speed displayed accurately? My RAM clock speed seems to be displayed a notch lower than advertised. My main concern is the RAM clock speed not the amount of RAM itself

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Answer 6

rkaufmann87

Level 10

140,880 points

Oct 3, 2020 7:13 AM in response to DanieIR1

You bought the wrong RAM, you should have purchased the correct speed RAM from Crucial.com or MacSales.com. iMacs are very sensitive to having quality and the correct RAM installed. Why would you buy an expensive computer like and iMac and then mess around by installing cheap and incorrect RAM. That just does not make sense. Please return RAM you bought and. purchase the correct RAM from Crucial.com (not Crucial brand from Amazon or some other reseller) or from Macsales.com!

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Answer 7

Old Toad

Level 10

207,763 points

Oct 3, 2020 3:13 PM in response to DanieIR1

The 2020 iMac don't use 3200MHz RAM. This screenshot is from the Tech Specs for the 2020 iMac:

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Answer 8

DanieIR1 Author

Level 1

10 points

Oct 6, 2020 7:00 PM in response to rkaufmann87

There is still a problem though. My 8GB RAM that came with the iMac reads as 2133MHz, but it should be 2666MHz. That is what apple advertised.

So to summarize

3200 reads as 2666

2666 reads as 2133

This happens for all the RAM I have tried, and I've tried each one independently.

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Answer 9

DanieIR1 Author

Level 1

10 points

Oct 6, 2020 7:32 PM in response to rkaufmann87

I just tried this, and while the reading is correct now, my performance(frame rates) is actually lower.

I learned from various sources that RAMs coupled together should occupy the same DIMM and different channels. (For example here https://www.ifixit.com/Answers/View/223429/How+to+couple+RAM+Modules+in+iMac+27). So I figured I'd put the 2x4GB in slots 1 and 3 and 2x16 in slots 2 and 4.

Is there any reason why I should do otherwise? As I said, my performance is lower, and other sources confirm this.

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Answer 10

BORg529

Level 4

3,057 points

Oct 7, 2020 12:25 AM in response to DanieIR1

Other people may give up, but not me. At least not yet! In my brand new 2020 27” 5K iMac, I had original 8gbs RAMS in 1&3, upgraded OWC 16gbs RAM in slots 2&4, speed was 2133MHz. Reinstalled to what rkaufmann87 said, RAM speed increased to 2667 MHz! Try install the right RAMS in the recommended slots, and go from there. If you still having issues, I don’t know.

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Answer 11

DanieIR1 Author

Level 1

10 points

Oct 7, 2020 12:27 AM in response to BORg529

The same thing happened to me. However, I did some more research, and it turns out that what actually happens is that the dual-channel feature is disable which allows each individual RAM to go at maximum speed. If you go back to 1/3 and 2/4, dual channel is enabled(which is much faster) but the compromise in intel processors is that you lose the speed. Again this only happens if you mix and match RAM, if you stick to just one set(so for instance just the 32GB) you Can have both. Check out the Reddit post I linked above. It explains it pretty well.

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Answer 12

Old Toad

Level 10

207,763 points

Oct 3, 2020 3:23 PM in response to DanieIR1

Not according to the Tech Specs: Tech Specs

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Answer 13

rkaufmann87

Level 10

140,880 points

Oct 2, 2020 11:01 PM in response to DanieIR1

You installed the upgraded RAM incorrectly. Please see how it should be installed below, note the slots the RAM is installed in:

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Answer 14

DanieIR1 Author

Level 1

10 points

Oct 2, 2020 11:15 PM in response to rkaufmann87

This is how it's currently installed. What slots should they be in? Should they be right next to each other or be in slots 1/3 or 2/4?I have 2x16 by the way

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Answer 15

Old Toad

Level 10

207,763 points

Oct 3, 2020 3:03 PM in response to DanieIR1

Sometimes the RAM modules offered at Amazon don't pass all of the strict QC tests whereas those directly from MacSales or Crucial do.

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iMac RAM speed not displayed accurately

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