Restrictions on Newly-Installed Memory

sidlerg

macrumors newbie
Original poster
Feb 10, 2019
3
0
Central Florida
I have an iMac (Retina 5K, 27-inch, 2017) desktop, running macOS Mojave (v 10.14.3), with 8 GB DDR4 memory (taking up two of four slots), with a capability for an upgrade to 64 GB... supposedly.

My question is two-fold:
FIRST, with a recent purchase of an additional 4 GB memory card, is the system receptive to (will it recognize) a single/additional (4 GB) card, or does it have to be of equal value, distributed between both available (open) slots? I have installed the new card among the other two (4 GB) cards but the system doesn't reflect the increased memory/capability?

SECOND, I am somewhat bothered by the back-and-forth threads that claim the unit of not being able to exceed 24 GB???
 

SaSaSushi

macrumors 601
Aug 8, 2007
4,084
479
Takamatsu, Japan
FIRST, with a recent purchase of an additional 4 GB memory card, is the system receptive to (will it recognize) a single/additional (4 GB) card, or does it have to be of equal value, distributed between both available (open) slots? I have installed the new card among the other two (4 GB) cards but the system doesn't reflect the increased memory/capability?
You can add single modules of properly spec'd RAM but matching modules in pairs will deliver optimal performance (dual-channel mode).

SECOND, I am somewhat bothered by the back-and-forth threads that claim the unit of not being able to exceed 24 GB???
I haven't seen any back and forth on this topic. The 2017 iMac supports up to 64GB of RAM.

I'm currently running mine with 40GB. (2 x 4GB and 2 x 16GB)
 

jerwin

macrumors 68020
Jun 13, 2015
2,475
4,455
The imac comes with 8 gigabytes-- two 4-gigabyte SODIMMS.

For performance reasons it's useful to buy ram in pairs.

So, you can buy

two 4 GB SODIMMS-- giving yourself 16 GB total, but what if that's not enough?
two 8 GB SODIMMS-- giving yourself 24 GB total, at which point you discover that your imac does occasionally use 17 GB of memory
two 16 GB SODIMMS-- giving yourself 40 GB total, which might be sufficient for photoshop

four 8 GB SODIMMS-- for 32 GB, but throwing the Apple RAM on ebay.
four 16 GB SODIMMS-- for 64 GB, with the same "waste". If that's not enough, perhaps it's time for an imac pro?

24 GB isn't a limit. It's a sensible place to stop and reassess ones needs.

(Or do you have a 1 TB fusion drive? see https://tidbits.com/2017/08/07/imac-1-tb-fusion-drives-have-smaller-ssds/)
 
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sidlerg

macrumors newbie
Original poster
Feb 10, 2019
3
0
Central Florida
Thx for the input. The fact is that I received a (single) 4 GB memcard (I am aware that pairing cards is desired) that should have upped the onboard to 12 GB; however, with the card installed it does not show (recognize) any change?
[doublepost=1549897337][/doublepost]
what does the system Information app say?
Unfortunately, it shows no increase in total memory; part of the reason for my earlier questions of whether the system will only read (react) to cards being installed in pairs.
 

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mreg376

macrumors 65816
Mar 23, 2008
1,120
309
Brooklyn, NY
I don't know what back-and-forth threads you're talking about either. You don't say what brand the RAM is, where you bought it, or the specs. It could be bad RAM. After having spent the money for a superb 27" iMac, you should add quality, properly spec'd RAM in a configuration that everyone know works well for sure -- pairs.
 

Fishrrman

macrumors P6
Feb 20, 2009
17,425
5,646
Remove the card and try it in the other slot.

Are you SURE you bought the correct DIMM for the job?
 

sidlerg

macrumors newbie
Original poster
Feb 10, 2019
3
0
Central Florida
The product is an OWC memory board (card). Supporting 2400MHz DDR4 PC4-19200.

As for the thread re: mem cap restrictions, there is a TON of it within this very forum; which is what led me to the concerns of stated cap vs. max performance cap.
 

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jerwin

macrumors 68020
Jun 13, 2015
2,475
4,455
Click on the System Report button (in the About this mac window)

Then click on the memory tab.

You should see something like this (albeit with faster memory).

Screen Shot 170.png


Apple installs its ram in bank 0. You presumably installed your OWC stick in bank 1. The System Information tab will let us know if that's the case.