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Mixing RAM in 2020 iMac?

H

hky740

macrumors member
Original poster
Dec 20, 2019
64
6
I have a mid-2020 27 inch iMac on order. Given Apple's RAM prices, I bought a 32 GB kit (16X2) from OWC and will just upgrade the RAM myself as I have on Windows-based systems over the years.

Would there be any harm in leaving the 8 GB RAM in there that comes with the iMac for a total of 40 GB? 16x2 and what I assume is 4x2.
 
No harm, but (slightly) degraded performance, which likely negates the benefit of the extra 8GB RAM.
Read the several ongoing threads on this topic, such as:
Memory upgrade troubleshooting in 2020 27-inch iMacs
 
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hky740 said:
I have a mid-2020 27 inch iMac on order. Given Apple's RAM prices, I bought a 32 GB kit (16X2) from OWC and will just upgrade the RAM myself as I have on Windows-based systems over the years.

Would there be any harm in leaving the 8 GB RAM in there that comes with the iMac for a total of 40 GB? 16x2 and what I assume is 4x2.
Click to expand...

I think you would be better off returning it an getting a new one with only 8GB. You paid a huge plus for those additional 24GB.
 
hky740 said:
I have a mid-2020 27 inch iMac on order. Given Apple's RAM prices, I bought a 32 GB kit (16X2) from OWC and will just upgrade the RAM myself as I have on Windows-based systems over the years.

Would there be any harm in leaving the 8 GB RAM in there that comes with the iMac for a total of 40 GB? 16x2 and what I assume is 4x2.
Click to expand...

dont mix with apple ram it get downclocked at 40 gigs or you lose duel channel and keep the 2667. just use the 32 gigs from OWC in slots 1 and 3 should be where the apple ram is
 
hky740 said:
I have a mid-2020 27 inch iMac on order. Given Apple's RAM prices, I bought a 32 GB kit (16X2) from OWC and will just upgrade the RAM myself as I have on Windows-based systems over the years.

Would there be any harm in leaving the 8 GB RAM in there that comes with the iMac for a total of 40 GB? 16x2 and what I assume is 4x2.
Click to expand...
Yes there is I just found out the hard way Apple has a new message out on Sept 2
iMac (Retina 5K, 27-inch, 2020) DIMMs have a notch on the bottom, slightly left of the middle. If your DIMMs are mixed in capacity, minimize the capacity difference between Channel A (slots 1 and 2) and Channel B (slots 3 and 4) when possible.
For optimal memory performance, DIMMs should be the same capacity, speed, and vendor. Use Small Outline Dual Inline Memory Modules (SO-DIMM) that meet all of these criteria:
8 gb it ships with cant ber used.. Also
  • So you cannnot mix RAM the 8 GB it ships with cant be used.. I ran geekbench testing with the 40 MB config HUGE performance downgrade BE carefull this only happens on the IMAC 2020
 
My iMac came configured from the factory with 4 GB DIMMS in slots 2 and 4, not 1 and 3. Slots 2 and 4 are identified as DIMM 0 for memory channels A and B, respectively, and slots 1 and 3 are DIMM 1 for each memory channel. I would think that you would want to populate the lower numbered DIMMs first, no? That would be DIMM 0, or slots 2 and 4.
 
You get it to work BUT it puts the memory in single channel mode Apple came out with an advisory stating that you cant mix memory. The performance of the machine is degraded badly in single channel mode I have 64 k on 2 chips now in 2 and 4 I think I should have done 4 16GB chips in all 4 slots..
 
jtighe8 said:
You get it to work BUT it puts the memory in single channel mode Apple came out with an advisory stating that you cant mix memory. The performance of the machine is degraded badly in single channel mode I have 64 k on 2 chips now in 2 and 4 I think I should have done 4 16GB chips in all 4 slots..
Click to expand...
2x32GB in slots 2 & 4 is perfectly fine.
There are some reports/claims than 4x16GB gives slightly faster benchmark scores than 2x32GB, but not worth worrying about. There is probably more variation from test to test.
 
i ran several geekbench5 tests when I had 72 MB in 2 32 and 2 4 it was very slow in parts of the test.. Multiscore 7212 with 72 MB 8711 with only 64 MB.. Big difference
 
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AZREOSpecialist said:
My iMac came configured from the factory with 4 GB DIMMS in slots 2 and 4, not 1 and 3. Slots 2 and 4 are identified as DIMM 0 for memory channels A and B, respectively, and slots 1 and 3 are DIMM 1 for each memory channel. I would think that you would want to populate the lower numbered DIMMs first, no? That would be DIMM 0, or slots 2 and 4.
Click to expand...
I agree, and those are the slots that the Apple sticks are installed in.
In theory slots 1 and 3 should do the same as slots 2 and 4, but when I tried slots 1 and 3 the computer would not boot. Maybe it was just me, as I think slots 1 and 3 have worked for others. (This is using only 2 sticks).
 
I’am replacing my RAM with crucial 2x32 in a IMAC 2020 27 inch I’am seeing conflicting opinions on the best slots to put these in RAM modules in. I’am taking out the original 2x4 RAM which comes with the IMAC . Which slots should I use for the optimal performance
thanks hal
 
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