Late 2015 iMac memory

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Level 1

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Late 2015 iMac memory

According to Apple's specs my late 2015 27" Retina iMac can only hold a maximum of 32 GB of ram.

It takes PC3-14900 1867MHz DDR3 SDRAM SODIMMs - I currently have 8GB chips in each of the 4 slots. Can I install 16GB chips into these slots? If so, do I have to do it in pairs? The specs say nonparity, not sure if that's what that means. A pair of 16GB chips are really expensive. I was thinking of maybe buying one and swapping out one of the 8GB chips. Any suggestions or comments? Thanks, Carl

iMac 27″, macOS 11.6

Posted on Nov 3, 2021 9:04 AM

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Answer 1

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Phil0124

Level 10

216,884 points

Nov 3, 2021 10:33 AM in response to carlart

While it's recommended to install them in pairs for best performance, there is no real issue in installing just one. Yes, it won't be as fast as a pair, but it also won't have any real adverse effects.

Yes, that model can go up to 64GB or RAM.

See here: link-> https://eshop.macsales.com/shop/memory/iMac/Retina-5K2015/DDR3L

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Answer 2

Phil0124

Level 10

216,884 points

Nov 3, 2021 11:04 AM in response to dialabrain

dialabrain wrote:

Phil0124 wrote:

While it's recommended to install them in pairs for best performance, there is no real issue in installing just one. Yes, it won't be as fast as a pair, but it also won't have any real adverse effects.

FWIW, lower performance seems to be an adverse effect. Maybe it's just me. And also FWIW, It seems to me there have been posts on ASC where users had problems installing one unmatched module. I could be remembering that incorrectly.

I would mention there's probably a good reason PCs and Macs come with 4, 8, 16, 32, 64, 128… GBs and not in between amounts.

The slowdown in most cases is almost imperceptible in normal use if at all perceptible. You would need an actual benchmark to tell its actually slower than a similar amount of matched RAM.

With good quality RAM like that from OWC, there should be no issue with it being unmatched.

I'd say always go for more RAM over matched RAM if its not possible or convenient to get matched RAM.

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Answer 3

Jack-19

Level 8

46,188 points

Nov 3, 2021 9:25 AM in response to carlart

+1 - Install in pairs.

Also, only buy from OWC. Crucial is the other excellent Mac memory vendor, however, they do not offer memory for your model of iMac.

Jack

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Answer 4

dialabrain

Level 10

135,821 points

Nov 3, 2021 10:55 AM in response to Phil0124

Phil0124 wrote:

While it's recommended to install them in pairs for best performance, there is no real issue in installing just one. Yes, it won't be as fast as a pair, but it also won't have any real adverse effects.

FWIW, lower performance seems to be an adverse effect. Maybe it's just me. And also FWIW, It seems to me there have been posts on ASC where users had problems installing one unmatched module. I could be remembering that incorrectly.

I would mention there's probably a good reason PCs and Macs come with 4, 8, 16, 32, 64, 128… GBs and not in between amounts.

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