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wilberforce

macrumors 65816
Aug 15, 2020
1,370
1,277
SF Bay Area
Hi guys, read through this topic here and would like to say thanks to all the contributors that made this happen :)
Decided to purchase CT32G4SFD8266 from amazon, 2 sets of (32gbx2) a total of 128gb.

Received my ram today and slotted it in but got some questions I hope you guys can help with. Noted that Lime666 and cczhu pretty similar issue as me. But I am hoping to get some advice on how I should proceed please.

1. I ordered 2 sets of CT32G4SFD8266 (32gb x 2) x 2. I made separate orders for each set. However I received 1 set labeled CT32G4SFD8266 and the other 16ATF4G64HZ. Are these the same? (I checked with crucial chat on the website and they said to contact Amazon as the 16ATF4G64HZ falls under Micron and that the Amazon seller named Crucial is actually a reseller.)

2. When I installed them in the iMac 2020 today, I did 2 configs, AABB one which gave me 2667 speed and the other ABAB which gave me 2133. So was pretty happy when I saw 2667 till I watched a video regarding single and dual channel ram setup which can affect performance? totally lost at this point.

the vid I watched. jump to 6.42 shortcut in the comments

3. What should I do? Have attached a pic in the 2133 setup FYI. Should I go to the AABB setup? which gives me 2666, but if I understand correctly is not dual channel mode.

Hope I didn't miss out some solution/explanation in the previous posts but I read through a few times and where I got confused is in the single channel dual channel thing. where you could still have 2667 speed but diminished performance.

Thanks in advance :)
The only requirement for dual channel is that the sticks in each channel are the same size (GB). (Assuming they have same speed, latency and rank, to avoid problems.) You are fine with AABB. This has been tested and confirmed by several people in these forums, including by me.
You can convince yourself by running Novabench RAM speed test several times (with no other processes running). You should get about 28000 MB/s if running in dual channel at 2667 MHz.
 
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robbie1056

macrumors newbie
Nov 11, 2020
10
2
hi all.i am new to all this and just ordered 27 inch 2020 imac,never used mac ios either before
i want to upgrade the ram and wondered if any of the below is better or not
just to confirm if someone can just say yes or no.
1, i cannot add ram in 2 slots and keep the existing apple 2 x 4gb in the other 2 slots
2. 2 x 16gb in 2 slots only and 2 empty(if so what slots?)
3. 4 x 8gb in all 4 slots
even though option 2 and 3 would be the same 32gb would either make a difference
i was going to use crucial-do i need to go for the option with the M at the end?i.e

Crucial CT2K8G4S266M 16 GB Kit (8 GB x2)​

as it will be a new imac-am i right in installing the ram before i switch it all on
thanks for any advice
i have been reading the posts but a little confused
 

wilberforce

macrumors 65816
Aug 15, 2020
1,370
1,277
SF Bay Area
hi all.i am new to all this and just ordered 27 inch 2020 imac,never used mac ios either before
i want to upgrade the ram and wondered if any of the below is better or not
just to confirm if someone can just say yes or no.
1, i cannot add ram in 2 slots and keep the existing apple 2 x 4gb in the other 2 slots
2. 2 x 16gb in 2 slots only and 2 empty(if so what slots?)
3. 4 x 8gb in all 4 slots
even though option 2 and 3 would be the same 32gb would either make a difference
i was going to use crucial-do i need to go for the option with the M at the end?i.e

Crucial CT2K8G4S266M 16 GB Kit (8 GB x2)​

as it will be a new imac-am i right in installing the ram before i switch it all on
thanks for any advice
i have been reading the posts but a little confused
Some answers:
1. Technically, you can add RAM in 2 slots and keep the 2x4GB in the other two slots, but memory speed will be degraded. Thus most prefer to remove the Apple RAM, as it is better to run the RAM at full speed, rather than have slightly more RAM all running at a lower speed. Short answer: you are correct.
2. Put 2x16GB in slots 2 and 4 (where slot 1 is at top).
3. 4x 8GB in all four slots will also work, but there is no advantage. (Some claim this is slightly faster, but that is very debatable, as the normal variation in test results is more than any perceptible difference). It will cost slightly more than 2x16GB, and also leaves you with no open slots if you want to add more RAM in the future.
4. The crucial kit that you cite is a good choice, and the M suffix indicates it is "for Mac" and guaranteed as such. However, many have used the non-M version with no problems, and surmise it is just marketing/environmental, as there does not appear to be any real substantive difference (maybe more testing). However, instead of 4x8GB, I would suggest this 2x16GB kit which is what i am using : CT2K16G4S266M

5. Many other kits work just as well. I tested this one and it was just as good, and is a great price, and is also guaranteed for Mac:

6. I actually suggest do not install the RAM before you turn it all on. Make sure it all works fine with the Apple RAM first. Then once everything is installed, running to your satisfaction, turn it off and switch out the RAM. Important note: after changing RAM, the Mac will take extra time to boot up, and appear to be completely black and unresponsive for an extra minute: do not worry, it is not broken! It is also quite easy to not get the RAM seated properly.
Hope this helps.
 
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robbie1056

macrumors newbie
Nov 11, 2020
10
2
Hi Wilberforce
thanks very much for the in depth reply,really useful and just what i needed
also the advice on starting up once i take the mac out the box and run everything first then install the ram
think ill go for the crucial 2x16 gb option
im only gonna use it to surf the web,emails looks at some photos etc,,not going to really edit anything,would 32gb be too much too start
thank you
 
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wilberforce

macrumors 65816
Aug 15, 2020
1,370
1,277
SF Bay Area
Hi Wilberforce
thanks very much for the in depth reply,really useful and just what i needed
also the advice on starting up once i take the mac out the box and run everything first then install the ram
think ill go for the crucial 2x16 gb option
im only gonna use it to surf the web,emails looks at some photos etc,,not going to really edit anything,would 32gb be too much too start
thank you
Nowadays 2x16GB is a kind of sweet spot for price.

But for your use case, 2x8GB would probably be fine.
Unless you are one of those that like to have lots (like dozens) of tabs open in a web browser, which can can consume remarkably large amounts of RAM - Chrome is notorious for this.

You might consider staying with the stock 2x4GB for a while, and keep an eye on the "memory pressure" in the Activity Monitor. If it gets out of the green zone, or it shows high "Swap Used," you need more RAM. There is nothing wrong with using only 8GB for simple tasks, I have been using 8GB on my Macbook for this purpose for 5 years no problem.

Activity-Monitor-Memory-Pressure.png
 

Megabass

macrumors member
Nov 5, 2020
39
12
Moscow, Russia
Some answers:
1. Technically, you can add RAM in 2 slots and keep the 2x4GB in the other two slots, but memory speed will be degraded.
The problem of low speed is solved by installing memory modules in the same channel as Apple memory.
Example:
1 slots 4Gb Apple
2 slots 4GB Apple
3 slots New RAM
4 slots New RAM
In this case, the speed will be maximum
 

wilberforce

macrumors 65816
Aug 15, 2020
1,370
1,277
SF Bay Area
The problem of low speed is solved by installing memory modules in the same channel as Apple memory.
Example:
1 slots 4Gb Apple
2 slots 4GB Apple
3 slots New RAM
4 slots New RAM
In this case, the speed will be maximum
For the benefit of others, this arrangement is not entirely correct:
Apple RAM comes installed in Slots 2 and 4, not 1 and 2.
If the new RAM is not the same size as Apple RAM, dual channel mode is lost (it uses flex mode instead).
 

Megabass

macrumors member
Nov 5, 2020
39
12
Moscow, Russia
For the benefit of others, this arrangement is not entirely correct:
Apple RAM comes installed in Slots 2 and 4, not 1 and 2.
If the new RAM is not the same size as Apple RAM, dual channel mode is lost (it uses flex mode instead).
It does not matter what channels Apple RAM stands for - the main thing is that it is installed with new modules. There are many examples on youtube, here is one of them
The user has 4 RAM modules: 2x4 Apple and 2x8 Crucial, in total 24GB at the frequency 2666Mhz
 

wilberforce

macrumors 65816
Aug 15, 2020
1,370
1,277
SF Bay Area
It does not matter what channels Apple RAM stands for - the main thing is that it is installed with new modules. There are many examples on youtube, here is one of them
The user has 4 RAM modules: 2x4 Apple and 2x8 Crucial, in total 24GB at the frequency 2666Mhz
See timestep 7:03 in this video for explanation why you should not mix RAM sizes in the 2020 iMac

It is not a problem for other iMacs, only for the 2020 iMac
 

robbie1056

macrumors newbie
Nov 11, 2020
10
2
For the benefit of others, this arrangement is not entirely correct:
Apple RAM comes installed in Slots 2 and 4, not 1 and 2.
If the new RAM is not the same size as Apple RAM, dual channel mode is lost (it uses flex mode instead).
hi wilberforce-if i kept the 2 x apple ram and added another 2 4gb ram in the other two slots would this work,or does it have to be all the same size and brand..thanks
 

wilberforce

macrumors 65816
Aug 15, 2020
1,370
1,277
SF Bay Area
ok great maybe ill just order 2 x 4gb of crucial and use the apple ram and make it to 16gb..thanks
Not sure 2x4GB crucial is available for 2667MHz RAM

Edit: maybe it is:
 
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kungfuthug

macrumors newbie
Nov 12, 2020
5
0
any one ordered from crucial.com in the past? how long does it take for them to ship? My order has been "in process" for more than 24 hours. Ordered my CT2K32G4S266M from there cause Amazon didn't have it in stock.
Hi. How did that RAM work in your 2020 iMac? I have the ability to buy 64GB for cheap. Does it work?
 

robbie1056

macrumors newbie
Nov 11, 2020
10
2

x83

macrumors newbie
Nov 10, 2020
3
2
The only requirement for dual channel is that the sticks in each channel are the same size (GB). (Assuming they have same speed, latency and rank, to avoid problems.) You are fine with AABB. This has been tested and confirmed by several people in these forums, including by me.
You can convince yourself by running Novabench RAM speed test several times (with no other processes running). You should get about 28000 MB/s if running in dual channel at 2667 MHz.

Hi Wilberforce, thank you for your reply! Switched to AABB and ran nova benchmark as you recommended.

Thanks for highlighting the requirement that all the ram just needs to be the same size.

Based on what you mentioned, looks like everything is sweet. Have attached the pic for anyone who might find the info useful, included the highest and lowest score.
 

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x83

macrumors newbie
Nov 10, 2020
3
2
You got ram from a 3rd party seller. Always, ALWAYS buy only from Amazon.com. It should say "Sold by and shipped by Amazon.com" on the right side. Anything else is a gamble, like you just found out. This "reseller" (who is pretending to be crucial) shipped you whatever was on the shelf, hoping you wouldn't notice.

Send it all back and buy a new set, ensuring you are actually buying from Amazon. Don't forget to leave a one-star review on the seller page because these jokers need to be flushed out.
Hi Warp9,

thank you for the advice regarding resellers, got mislead by thinking that there could be only one crucial username on amazon. My mistake.

Def gonna leave that review as you recommended. Just wanted to say thanks!
 
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Takuro

macrumors 6502a
Jun 15, 2009
557
244
FYI, the CT2K32G4S266 (memory kit most people seemed to recommend in this thread) is back down to $160 on Amazon for Black Friday.

 

MarvinHC

macrumors 6502a
Jan 9, 2014
834
292
Belgium
Hi,
I am planning to buy a memory upgrade for my 2020 27" iMac I just ordered. Going for either 32GB or 64GB (might as well.. although probably ab it of an overkill)

I wanted to go for the Crucial CT32G4SFD8266 (so the one without the M since it is a lot cheaper). Amazon.FR offers it currently at a good price, but for a reason unknown to me it is cheaper to buy two single modules than a kit of 2. Any downside to buying individually?
Other question, if I would buy just one module of 32GB - can I make use of that or is it still like in the past that RAM modules should be installed in pairs?

 

wilberforce

macrumors 65816
Aug 15, 2020
1,370
1,277
SF Bay Area
Hi,
I am planning to buy a memory upgrade for my 2020 27" iMac I just ordered. Going for either 32GB or 64GB (might as well.. although probably ab it of an overkill)

I wanted to go for the Crucial CT32G4SFD8266 (so the one without the M since it is a lot cheaper). Amazon.FR offers it currently at a good price, but for a reason unknown to me it is cheaper to buy two single modules than a kit of 2. Any downside to buying individually?
Other question, if I would buy just one module of 32GB - can I make use of that or is it still like in the past that RAM modules should be installed in pairs?

Definitely install RAM in pairs, to get dual channel. If you only install one module, it will run in single channel, which effectively halves the RAM transfer speed.
It is fine to buy two single modules individually, as long as they are the exact same part number (as identified in Mac System Report - Memory, not on the label). Reason is that if you later add more RAM, so you have a total of 4 modules, the 2020 iMac wants to see the exact same part number in slots 1 & 2 and in slots 3 & 4 else it will drop the RAM speed from 2667 MHz to 2133 MHz (this is a quirk of only the 2020 iMac). If you only ever have two modules, I think it is not so important (although I have not personally tried two mismatched modules.)
Chances are that if you order two modules at the same time they will have exact same part numbers, but not guaranteed.
 
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MarvinHC

macrumors 6502a
Jan 9, 2014
834
292
Belgium
Thanks a lot, Wilberforce, for your answer. You refreshed my memory why they need to be installed in pairs.
So a pair it is, now just need to decide if 2x16 or 2x32 (and throwing out the original 2x4). My brains tell me 32GB is more than enough for the years to come... (this 2020 iMac will replace a 2010 (!) with 12 GB RAM)
 
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Optimistprime

macrumors newbie
Nov 30, 2020
2
0
Hello to everyone,

I live in Istanbul and i cant find the good seller and brands for this upgrades. I want to install 2x 32 GB RAM and upgrade to 64 GB RAM and get the best performance. Like everyone else :) I met many companies, but I did not get good results. I hope someone can help me!

My system:
Imac 2020 5K retina i7 3.8 - 8 Gb 2666 MHz DDR4

The products I could find:

  • Kingston KVR26S19D8/32 32 GB DDR4 2666 MHz CL19 Ram (125$)
  • Kingston 32GB DDR4 2666MHz CL19 Ram KCP426SD8/32 (210$)

What is the diffrence it looks the same? Which one is the best choice for my mac.


And also i found this one, link below. (230 $)

https://bilendenal.com/Bigboy-Apple-32GB-DDR4-2666MHz-CL19-Notebook-Rami-BTA026_32G.html

The seller said this brand has a samsung chipset and is 100% compatible with apple imac, but this is the first time I've heard of this brand.

Thanks!
 
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