Can you do 3x8GB of RAM?

Radiating

macrumors 65816
Original poster
Dec 29, 2011
1,018
7
Can you use 3 x 8gb or 2x 4gb + 2x 8gb with the imac? Will this impact performance at all?

I have an imac high end with 8gb and need at least 20 gb of ram. I was wondering if I could just pop in 2x8gb sticks from crucial or 3x8gb sticks and get full performance. Thanks.
 
Last edited:

martinm0

macrumors 6502a
Feb 27, 2010
563
25
Can you use 3 x 8gb or 2x 4gb + 2x 8gb with the imac? Will this impact performance at all?

I have an imac high end with 8gb and need at least 20 gb of ram. I was wondering if I could just pop in 2x8gb stocks from crucial or 3x8gb sticks and get full performance. Thanks.
Not sure about 3x 8GB, but you're good to go with 2x4GB and 2x8GB for 24GB total.
 

drambuie

macrumors 6502a
Feb 16, 2010
751
0
With 3 x 8GB put two DIMMs in the lower bank, (where the two 4GB modules are now), and the single DIMM in the upper bank. Then the lower 16GB will work in dual channel mode, and the single upper 8GB will work in single channel mode. With this arrangement there will be practically no noticeable impact on performance. Then you could add another 8GB DIMM later for a full 32GB.
 

martinm0

macrumors 6502a
Feb 27, 2010
563
25
I've been trying 2x8gb and 2x4gb on my mid 2010 11,3 i3 but with no luck
:mad:
Hmm. I did this on a 2011 21.5" and 2012 27" iMac without issue. I guess I'm not sure if there are some limitations to the 2010 models (maybe they don't support 8GB modules?). Will have to do some digging.
 

ccapman670

macrumors regular
May 31, 2012
133
0
New Orleans / Baton Rouge
That's because the Core i3 on the 27" won't handle more than 16 (4X4GB); only the upgraded i5 or i7 CPUs will.

Scroll down to the iMac "Core i3" section here:

http://www.everymac.com/systems/by_capability/actual-maximum-ram-capacity-of-macs.html
I have a late 2009 iMac 27" i5 2.66GHz. According to apple and crucial I can only have up to 16GB (4x4GB 1067). But EveryMac says 32GB.
http://www.everymac.com/systems/apple/imac/specs/imac-core-i5-2.66-27-inch-aluminum-late-2009-specs.html

Is EveryMac reliable? Anyone know why Apple wouldn't state this? Thanks for any insight anyone can provide!
 

justperry

macrumors G4
Aug 10, 2007
10,175
5,319
Home is everywhere and nowhere.
I have a late 2009 iMac 27" i5 2.66GHz. According to apple and crucial I can only have up to 16GB (4x4GB 1067). But EveryMac says 32GB.
http://www.everymac.com/systems/apple/imac/specs/imac-core-i5-2.66-27-inch-aluminum-late-2009-specs.html

Is EveryMac reliable? Anyone know why Apple wouldn't state this? Thanks for any insight anyone can provide!
Yes, everyMac is overall reliable.

Apple states what is available from them, not what is possible, they also say maximum HD on some earlier systems to be like 500 GB for instance but this is complete nonsense, Maximum HD size is only limited by what the OS can see, which is much much higher than 500 GB, it is more like ExaBytes but there are no HD's of that size.
 

ccapman670

macrumors regular
May 31, 2012
133
0
New Orleans / Baton Rouge
Yes, everyMac is overall reliable.

Apple states what is available from them, not what is possible, they also say maximum HD on some earlier systems to be like 500 GB for instance but this is complete nonsense, Maximum HD size is only limited by what the OS can see, which is much much higher than 500 GB, it is more like ExaBytes but there are no HD's of that size.
Thank you for the information! Some of what I read stated people were using 1333MHz 8GB chips as well even though mine supposedly needs 1066. I'm going to order some.
 

toddzrx

macrumors 6502a
Nov 20, 2012
722
258
Yes, everyMac is overall reliable.

Apple states what is available from them, not what is possible, they also say maximum HD on some earlier systems to be like 500 GB for instance but this is complete nonsense, Maximum HD size is only limited by what the OS can see, which is much much higher than 500 GB, it is more like ExaBytes but there are no HD's of that size.
Thank you for the information! Some of what I read stated people were using 1333MHz 8GB chips as well even though mine supposedly needs 1066. I'm going to order some.
As I understand it, Apple locks in the specs (for the device in question) at the time of manufacture, and they don't update them even when new hardware becomes available to consumers. So back in 2009, 8GB RAM sticks weren't available and Apple rightly published a max of 16GB in the iMac.
 

justperry

macrumors G4
Aug 10, 2007
10,175
5,319
Home is everywhere and nowhere.
As I understand it, Apple locks in the specs (for the device in question) at the time of manufacture, and they don't update them even when new hardware becomes available to consumers. So back in 2009, 8GB RAM sticks weren't available and Apple rightly published a max of 16GB in the iMac.
Yes/No, for instance, apple never uses the biggest HD sizes, so there are bigger ones but they don't say this.