Mixing RAM in 2020 iMac

[ErikGrim]

My 2 32Gb modules came in different weeks, so I installed just one along with my 2x4GB apple modules and the three of them all ran at 2666mzh (not ideal of course, but I was hitting that 8Gb limit pretty hard the very same day). When I put in my second 32Gb module yesterday they all dropped to 2133mhz. I'll probably chuck the 2x4Gb as the difference between 72Gb and 64Gb will be less noticeable than the clock reduction.

 

[Ashleyr]

Curious for recommendations:
iMac 2020 10 core i9
With 2x4gigs Apple ram

ordered owc 2x16gigs

Am I better just using 2x16=32 and leaving the 2x4 out?

or adding the 2x4 and getting 40 but either losing clock speed or dual channel.

I don’t do any editing or video... but have zoom, teams, email, chrome, photos, safari etc going and that, for some reason, can give my current 8gigs some grief.

advice? 32 or 40 in one of the configurations.

thanks

 

[wilberforce]

Curious for recommendations:
iMac 2020 10 core i9
With 2x4gigs Apple ram

ordered owc 2x16gigs

Am I better just using 2x16=32 and leaving the 2x4 out?

or adding the 2x4 and getting 40 but either losing clock speed or dual channel.

I don’t do any editing or video... but have zoom, teams, email, chrome, photos, safari etc going and that, for some reason, can give my current 8gigs some grief.

advice? 32 or 40 in one of the configurations.

thanks

You are better just using 2x16=32GB.
For your use 32GB should be plenty. Adding the extra 8GB will just degrade the speed of the 32GB.
If you really need more than 32GB (unlikely), the solution is to add another 2x16GB for a total of 64GB, which you can always do later after you see how it goes

 

[Ashleyr]

You are better just using 2x16=32GB.
For your use 32GB should be plenty. Adding the extra 8GB will just degrade the speed of the 32GB.
If you really need more than 32GB (unlikely), the solution is to add another 2x16GB for a total of 64GB, which you can always do later after you see how it goes

Perfect! Appreciate the reply. Assuming I should use slot 1 and 3 or 2 and 4 or insert the 16s where the 4s were. Ya?

 

[wilberforce]

Perfect! Appreciate the reply. Assuming I should use slot 1 and 3 or 2 and 4 or insert the 16s where the 4s were. Ya?

I used slots 2 and 4 (where slot 1 is at top), which is where the Apple RAM was placed.

Slots 1 and 3 should also work, but I found my machine would not boot when I tried this. Worked fine for others, though.

btw, when you change RAM it will take an extra 30 seconds to boot

 

[Marli]

Mine is set up like this (below), and is showing the 40 gig at full speed.. I did originally get 2 x 4 gig SIMMs, they were the same manufacturer, same spec, but looked different, and they would on run at 2133 Mhz. I replaced them with 2 x 16 gig Kingstone SIMMs

Kingston ValueRAM 16GB Single (1x16GB) DDR4-2666 C19 SO-DIMM

ValueRAM is Kingston's value-priced line of industry-standard, generic memory intended for customers who have white box or generic computer systems, or who plan to purchase memory by specification. ValueRAM is designed to industry specifications tested, is 100% tested and is available at...

www.ple.com.au

 

[Marli]

btw, when you change RAM it will take an extra 30 seconds to boot

OK, this is what was going on.. I was starting to get worried.. I didn't know this and hadn't noticed this in the past. Not that I have upgraded to many iMacs ram.

 

[wilberforce]

Mine is set up like this (below), and is showing the 40 gig at full speed.. I did originally get 2 x 4 gig SIMMs, they were the same manufacturer, same spec, but looked different, and they would on run at 2133 Mhz. I replaced them with 2 x 16 gig Kingstone SIMMs

View attachment 1686355

OK, the problem with your arrangement is that you have 16+16 GB in Channel A, and 4+4 GB in Channel B, which means it will not be running in dual channel.
At best, it will instead run in "flex mode," where 16 GB will run in dual channel (the 8 GB in Channel B plus 8 GB of the 32 GB in Channel A), and the remaining 24 GB in Channel A will run in single channel. This effectively halves the transfer speed of 24 GB of the RAM.
At worst, all 40 GB will run in single channel. (I am not sure if flex mode is even enabled for this iMac.)
You will do better to put 16 GB in Channel A (Slot 2) and 16 GB in Channel B (Slot 4) to get full dual channel, and leave the 4+4 GB out. (This is assuming you have the 2020 iMac).
You can check yourself by running Novabench RAM speed test both ways. You should get 28000+ MB/s if it is set up correctly.
Hope this helps.

 

[Marli]

Ok, Thanks, I will take a look..

 

[Marli]

It did make a difference,

40 gig original config

32 gig one in each channel

Config like this

 

[Marli]

@wilberforce Thanks for the heads up. I was originally only going to use the 32 gig, but when it just seemed to work I went with it.. Im not keeping up these days with all the subtleties these days. to busy..

I intended to wait for the M series iMac, but my old one just died one morning.. so got a 2020 for the interim..