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2019 iMac 27" RAM question

SuperMatt

macrumors 6502a
Original poster
Mar 28, 2002
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If one buys a new iMac with the minimum 8GB of RAM and buys a 2x8GB 16 GB kit, can it be added to the existing 8GB to go to 24GB? If so, should the 3rd-party RAM be put into the empty slots, or should the RAM be organized into matching pairs?
 

28Gauge

macrumors 6502a
Sep 4, 2011
661
393
DFW
If one buys a new iMac with the minimum 8GB of RAM and buys a 2x8GB 16 GB kit, can it be added to the existing 8GB to go to 24GB? If so, should the 3rd-party RAM be put into the empty slots, or should the RAM be organized into matching pairs?

Yes. Just install your two new sticks of RAM in the empty slots while leaving the original RAM alone.
 
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SuperMatt

macrumors 6502a
Original poster
Mar 28, 2002
823
6,739
Yes. Just install your two new sticks of RAM in the empty slots while leaving the original RAM alone.

Thanks! This is pretty great - $75 for a crucial 16GB kit from Newegg - get 24GB for less than half what Apple charges for 16!
 
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28Gauge

macrumors 6502a
Sep 4, 2011
661
393
DFW
Thanks! This is pretty great - $75 for a crucial 16GB kit from Newegg - get 24GB for less than half what Apple charges for 16!

Agreed. I don’t understand Apple’s pricing policy on RAM at all. I just installed 2x16 RAM sticks in my new iMac for $120 on top of the factory 8GB for a total of 40 GB. Apple wanted $600 to go from 8GB to 32GB.
 
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aman88

macrumors regular
Mar 21, 2019
115
18
I put the new ram where the original ram was and then the original in the empty slots... was that wrong?
 
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wardie

macrumors 6502a
Aug 18, 2008
511
159
The computer is reading all the ram (24 gb).

It will see it all but if you messed up the pairs of slots it won’t be quite as fast using the memory, because the pairs of sticks are able to run in dual-channel mode, but only if in the correct banks to pair up. Apple will have correctly done this when you got it, so together the original or new memory must be in the two slots the original memory was in, and the other pair in the other two slots. In my 2017 iMac the pairing is interleaved i.e. slots 1&3, 2&4 in pairs. Not sure about 2019. Not sure its easy to tell from system report but I’ve never looked.
 
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