Is this dual channel or not? And how can I tell.

[wilberforce]

Sorry to dig up an old thread but I have a very similar question.

I wanted to add 2 x 4 GB to my imac 2020 to make the total go to 16 GB. I found 2 SK Hynix modules which are exact same spec and differ only by 1 letter in the serial number. I though this would be OK to add to slot 1 and 3, But the memory now runs in 2133mhz.

I read I can change the apple ram to slot 1 and 2 and the new ram to slot 3 and 4 but will then lose dual channel support. But is this also the case with 4 x 4 GB modules? If not, will 4x 4 GB of the exact same serial number work without problems? i may be able to find the exact same serial number hynix modules.

I hope anyone can have the definitive answer. Thank you!

Put the original 2x4GB in slots 1 and 2, and the new Hynix 2x4GB in slots 3 and 4.

In the 2020 iMac (and only the 2020 iMac), the requirements for using 4 DIMMs are:

1. part numbers in slots 1 and 2 must match, else speed drops to 2133
2. part numbers in slots 3 and 4 must match, else speed drops to 2133
3. Total size (GB) in Channel A (slots 1+2) must equal total size in Channel B (slots 3+4), else it will not run in full dual channel. (The requirement for dual channel has nothing to do with matching part numbers).

The way to achieve these 3 requirements is to arrange the RAM as I indicated above.

Don't waste your time or money trying to find more sticks with identical part numbers. It will provide no real benefit.

 

[Niekw]

Put the original 2x4GB in slots 1 and 2, and the new Hynix 2x4GB in slots 3 and 4.

In the 2020 iMac (and only the 2020 iMac), the requirements for using 4 DIMMs are:

1. part numbers in slots 1 and 2 must match, else speed drops to 2133
2. part numbers in slots 3 and 4 must match, else speed drops to 2133
3. Total size (GB) in Channel A (slots 1+2) must equal total size in Channel B (slots 3+4), else it will not run in full dual channel. (The requirement for dual channel has nothing to do with matching part numbers).

The way to achieve these 3 requirements is to arrange the RAM as I indicated above.

Don't waste your time or money trying to find more sticks with identical part numbers. It will provide no real benefit.

Thanks so much. I will try it this afternoon. I read in several threads that the imac 2020 was so picky that changing the slots would put it back into single channel mode even with same size GB’s.

Is there any way to check once the switch has happened that dual channel mode works properly? The performance loss would be problematic to say the least.

Thanks for your help. Much appreciated!

 

[wilberforce]

Thanks so much. I will try it this afternoon. I read in several threads that the imac 2020 was so picky that changing the slots would put it back into single channel mode even with same size GB’s.

Is there any way to check once the switch has happened that dual channel mode works properly? The performance loss would be problematic to say the least.

Thanks for your help. Much appreciated!

There is nothing that will tell you "you are running in dual channel," at least not on a Mac.

You can run Novabench RAM speed test and should get around 28000 MB/s if all is OK. Run it several times, because if there is any background process running it will give a low reading. You only need to run the RAM tests, not the full suite of tests ("Tests" menu). (The other Novabench tests aren't the best, IMO)

Novabench - Free Computer Benchmark Software

Free benchmark software to test your computer's performance. Download Novbench for Windows and Mac.

novabench.com

 

[Niekw]

There is nothing that will tell you "you are running in dual channel," at least not on a Mac.

You can run Novabench RAM speed test and should get around 28000 MB/s if all is OK. Run it several times, because if there is any background process running it will give a low reading. You only need to run the RAM tests, not the full suite of tests ("Tests" menu)

Novabench - Free Computer Benchmark Software

Free benchmark software to test your computer's performance. Download Novbench for Windows and Mac.

novabench.com

I am getting about 26.000 so should be OK I guess. Thanks so much for your help, you saved me a lot of effort. Much appreciated.

 

[wilberforce]

I am getting about 26.000 so should be OK I guess. Thanks so much for your help, you saved me a lot of effort. Much appreciated.

Usually it is a bit better than 26000.
You can try different arrangements (like compare with just the original 2x4GB) if you are still doubtful.

 

[Niekw]

If I recall correctly the difference between single and dual channel should be more thab like 5%. So I guess a score between 26-27k should prove it is Dual channel?

*I had safari and spotify open during the test

 

[wilberforce]

If I recall correctly the difference between single and dual channel should be more thab like 5%. So I guess a score between 26-27k should prove it is Dual channel?

*I had safari and spotify open during the test

I think you should be fine.
If you want to see what single channel is like, just put DIMMs in slots 1 and 2. Probably get 18000 or so.

If you put the 4 DIMMs in how you had them originally, running at 2133 MHz, RAM speed test will probably drop to 24000 or so.

But I don't like to keep putting DIMMs in and out of slots too much, as I worry about damaging something.

Your speed may be reporting slightly lower because you have 16GB (I have 32GB). It shouldn't make a difference, but it seems to in the test. People with 64GB or 128GB get closer to 30000 MB/s. I suspect the speed isn't actually faster, but is a result of the testing method.

I think you are all good.

 

[wilberforce]

btw, the theoretical maximum bandwidth is
2667 MHz DDR, times 64-bit data channel, times dual channel
=340000 Mb/s, divided by 8 bits per Byte
=42000 MB/s

But this is not actually achieved in a test.

Single channel theoretical maximum would be (obviously) half that, i.e., 21000 MB/s. So anything faster than 21000 MB/s is not single channel.

A complication is that if the RAM in one channel is smaller than in the other channel, part of the RAM will run in dual channel mode, and part will run in single channel mode (This is known as "flex mode.") So there are actually three possible modes: single channel mode, full dual channel mode, and flex mode (a combination).

Sorry if this is too much info, you probably just wanted to know how to use your RAM!

 

[Niekw]

I think you should be fine.
If you want to see what single channel is like, just put DIMMs in slots 1 and 2. Probably get 18000 or so.

If you put the 4 DIMMs in how you had them originally, running at 2133 MHz, RAM speed test will probably drop to 24000 or so.

But I don't like to keep putting DIMMs in and out of slots too much, as I worry about damaging something.

Your speed may be reporting slightly lower because you have 16GB (I have 32GB). It shouldn't make a difference, but it seems to in the test. People with 64GB or 128GB get closer to 30000 MB/s. I suspect the speed isn't actually faster, but is a result of the testing method.

I think you are all good.

I trust this is OK for me. Really happy to be sure now. Thanks for helping me out.

 

[eftaefta]

I got the new 2020 iMac 27" with factory installed 16GBs of ram. I bought 2 8GB sticks of OWC ram. Both the Apple factory ram and the OWC ram were 2667MHz. At first I installed them in the 1 & 3 slots (Apple) and 2 & 4 slots (OWC). The RAM then showed 32GB at 2133MHz. Then I but the Apple RAM in slots 1 & 2 and the OWC RAM in slots 3 & 4. The system check then said I have 32GB of RAM at 2667MHz.

I then read some post that said if I configure it like I did at the end, I would be running a single channel as opposed to a dual channel. Is this true? How would I know? I can I check to see?

Any advise or comments would be greatly appreciated.

In the 2020 iMac (and only the 2020 iMac), the requirements for using 4 DIMMs are:

1. part numbers in slots 1 and 2 must match, else speed drops to 2133
2. part numbers in slots 3 and 4 must match, else speed drops to 2133
3. Total size (GB) in Channel A (slots 1+2) must equal total size in Channel B (slots 3+4), else it will not run in full dual channel. (The requirement for dual channel has nothing to do with matching part numbers).

 

[bithereandthere]

Duplicate

 

[bithereandthere]

Put the original 2x4GB in slots 1 and 2, and the new Hynix 2x4GB in slots 3 and 4.

In the 2020 iMac (and only the 2020 iMac), the requirements for using 4 DIMMs are:

1. part numbers in slots 1 and 2 must match, else speed drops to 2133
2. part numbers in slots 3 and 4 must match, else speed drops to 2133
3. Total size (GB) in Channel A (slots 1+2) must equal total size in Channel B (slots 3+4), else it will not run in full dual channel. (The requirement for dual channel has nothing to do with matching part numbers).

The way to achieve these 3 requirements is to arrange the RAM as I indicated above.

Don't waste your time or money trying to find more sticks with identical part numbers. It will provide no real benef

Thanks! You just saved me a ton of time

 

[Talvigi]

Hi guys, so all this is very confusing to me, I have an iMac 14,2 27inch (late 2013) core i5. I bought it used with two memory sticks of 4GB (4GBx4GB=8GB), but to my surprise within the same day it burned out a memory stick and turned off. I was shocked when it went off, but when i opened the RAM door and took out both ram slots; put one and checked if works? it worked. The other didn't work, so i realized it was the RAM which burned out.

Now when i looked closely, i found that one of them (the damaged one) was PC3 12800S 2Rx8, while the other (remaining one) was a PC3L 12800S 1Rx8. My surprise is that if my iMac does support PC3 than why it burned the RAM? While PC3L is alive.

And now i have two memory sticks, a 4gb PC3L 12800S 1Rx8 11-12-B4 SK-Hynix and an 8gb PC3L 12800S 2Rx8 11-13-F3 Samsung.

They are in the following DIMM SLOTS and are working fine since this morning without shutting down the system.

8GB Bank1/DIMM0 (Both RAMs are PC3L 12800S)
4GB Bank1/DIMM1

 

[wilberforce]

Hi guys, so all this is very confusing to me, I have an iMac 14,2 27inch (late 2013) core i5. I bought it used with two memory sticks of 4GB (4GBx4GB=8GB), but to my surprise within the same day it burned out a memory stick and turned off. I was shocked when it went off, but when i opened the RAM door and took out both ram slots; put one and checked if works? it worked. The other didn't work, so i realized it was the RAM which burned out.

Now when i looked closely, i found that one of them (the damaged one) was PC3 12800S 2Rx8, while the other (remaining one) was a PC3L 12800S 1Rx8. My surprise is that if my iMac does support PC3 than why it burned the RAM? While PC3L is alive.

And now i have two memory sticks, a 4gb PC3L 12800S 1Rx8 11-12-B4 SK-Hynix and an 8gb PC3L 12800S 2Rx8 11-13-F3 Samsung.

They are in the following DIMM SLOTS and are working fine since this morning without shutting down the system.

8GB Bank1/DIMM0 (Both RAMs are PC3L 12800S)
4GB Bank1/DIMM1

View attachment 2066136

This "works" (obviously), but by having all your RAM in Bank 1, the memory is operating in single channel mode, effectively halving the memory transfer speed.
To get full dual channel mode you need to have an equal amount of RAM installed in Bank 0 as in Bank 1.

 

[Talvigi]

This "works" (obviously), but by having all your RAM in Bank 1, the memory is operating in single channel mode, effectively halving the memory transfer speed.
To get full dual channel mode you need to have an equal amount of RAM installed in Bank 0 as in Bank 1.

Thanks for the wonderful words, I really didn't expect this much fast answer. So now, please let me know what should I do? Like it's for sure that I have ordered two more 4GB Ram sticks (PC3 12800). Now I will have an 8GB PC3L and two 4GB PC3. What should be their best location? I don't know the dual channel things, I only want a snappy Mac which works fine on most of it's tasks. Thanks a lot and God Bless You.

 

[wilberforce]

Thanks for the wonderful words, I really didn't expect this much fast answer. So now, please let me know what should I do? Like it's for sure that I have ordered two more 4GB Ram sticks (PC3 12800). Now I will have an 8GB PC3L and two 4GB PC3. What should be their best location? I don't know the dual channel things, I only want a snappy Mac which works fine on most of it's tasks. Thanks a lot and God Bless You.

The objective is to equalize the total GB in each Bank, as close as possible (Bank is another name for Channel.) For example:
8GB Bank1/DIMM0
4GB Bank0/DIMM0
4GB Bank0/DIMM1

If the GB is not equal in each Bank it is not ideal, but in reality it doesn't make that much difference to overall computer speed, as RAM transfer speed is only one of many factors that contribute to overall performance. Amount of RAM is generally more important than speed of RAM.

However you have a mixture of PC3 (1.50V) and PC3L (1.35V), so I am not sure how this will work. 2013 iMac is supposed to use PC3 sticks, but it is likely that most PC3L sticks will work also. I don't know if mixing them will work. Best would be to get all sticks the same size and type, but I suppose you can try.