This is the default and correct configuration. In dual channel operation each bank is 'attached' to a channel.
You want one memory kit in the DIMM0 slots and the other kit in the DIMM1 slots.
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27" RAM Upgrade - why not 24GB?
- Thread starter rick.m650
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You want one memory kit in the DIMM0 slots and the other kit in the DIMM1 slots.
Well it seemed like you didn't. I mentioned 12GB on each channel which means 12GB in 2 RAM slots. The math isn't hard after that
YOU ARE WRONG... DEAD WRONG......
Yes the memory must be paired... but it must be MATCHING pairs.
Not 8+4+8+4.... .but 8+8+4+4
8 gig in one pair.. and 16 gig in the other... NOT 12 in one and 12 in the other.
IT WILL NOT WORK PROPERLY.....
So just leave the Apple installed memory alone (assuming you want 24g), and add a matched pair of 16gig to get the 24gig.
Yes it's from a Wiki article.
And yes the iMac comes with one stick in bank o and one in bank 1 that's exactly why you have to rearrange if you want to add 2 8 gig dimms.
For correct dual channel you have to have the two 4 dimms in one bank and the two 8's in the other bank
How difficult is this to understand?
Yup, this is why you install ram in pairs. all the pairs don't need to be identical though.
Correction: 12 + 12 will work, but at slightly lower speed........because not in the correct dual channel mode.
I think, but am not completely sure, that apple has the original memory in one bank (call it bank 0). Bank 1 is therefore empty. This is the arrangement if they are using the memory in dual channel mode (which I cannot think of them not doing and have not heard anywhere that the imac runs ram in single channel mode). Therefore the empty ram slots represent bank 1. So you should just place your ram in the empty slots, no rearrangement necessary.
Just added the 16GB kit from Crucial into the two empty slots and all seemed fine until I checked Apple Hardware Test and I'm getting the attached error despite System Profiler showing no problems (also attached). I've since tried various configurations of the modules with retesting after each and only when I remove the new memory completely am I error free.
Any ideas?
Any ideas?
Attachments
You are wrong......
According INTEL specification:
In order to perform optimal each channel has to contain dimms with equal amounts of ram
The stock iMac has a 4 gig dimm in each channel ( bank 0 and bank 1) correct, as long as you don't add dimms with different amount of ram.
If you add an 8 gig dimm in each bank the dimms per bank are not the same amount (namely 4 and 8)
In order to obtain optimum dual channel performance you have to put the 4 gig dimms in one channel (bank 0 ) and the two 8 gigs in the other bank/channel
So you can add two 4 gig dimms in the free slots of an stock iMac, but if you are going to add two 8 gig dimms you have to rearrange: the two 4 gigs in bank 0 and the two 8 gigs in bank 1
Ok I am still very confused after reading these 3 pages.
Let's dumb it down for me please.
We have 4 slots. The 4GB RAM slots were installed in slots 1 and 3. So there were 2 empty slots.
I put the 8GB of RAM in slots 1 and 3. So I took out the original RAM. And put the 4GB of RAM in slots 2 and 4.
Is that ok?
My Memory reads:
Bank 0/DIMM0 8GB
Bank 1/DIMM0 8GB
Bank 0/DIMM1 4GB
BANK 1/DIMM1 4GB
Let's dumb it down for me please.
We have 4 slots. The 4GB RAM slots were installed in slots 1 and 3. So there were 2 empty slots.
I put the 8GB of RAM in slots 1 and 3. So I took out the original RAM. And put the 4GB of RAM in slots 2 and 4.
Is that ok?
My Memory reads:
Bank 0/DIMM0 8GB
Bank 1/DIMM0 8GB
Bank 0/DIMM1 4GB
BANK 1/DIMM1 4GB
I'm at a loss. I've tried these two configurations (attached) as well. Both returning similar errors. Is it possible that Apple Hardware Test is out to lunch or that I have a sketchy memory module? Is it potentially harmful to leave it setup like this?
Attachments
According to Intel "Dual-channel (interleaved) mode:
This mode offers higher memory throughput and is enabled when the memory capacities of both DIMM channels are equal. When using different speed DIMMs, the slowest memory timing will be used."
Apple preinstalls the 2x4gb dimms into bank0/dimm0 and bank1/dimm0 (channel A), similar to the following "Intel" diagram:
When you install additional 2x8gb dimms, you want to put them into the emty slots, similar to the following "Intel" diagram:
In this way, channel A (bank0/dimm0 + bank1/dimm0) = matching 4gb dimms, and channel B (bank0/dimm1 + bank1/dimm1) = matching 8gb dimms. Per the previous description, the capacities of both dimms per channel are equal.
Summary: Don't move around the preinstalled dimms, just install your new dimms into the empty slots.
Last edited:
According to Intel "Dual-channel (interleaved) mode:
This mode offers higher memory throughput and is enabled when the memory capacities of both DIMM channels are equal. When using different speed DIMMs, the slowest memory timing will be used."
Apple preinstalls the 2x4gb dimms into bank0/dimm0 and bank1/dimm0 (channel A), similar to the following "Intel" diagram:
When you install additional 2x8gb dimms, you want to put them into the emty slots, similar to the following "Intel" diagram:
In this way, channel A (bank0/dimm0 + bank1/dimm0) = 12gb, and channel B (bank0/dimm1 + bank1/dimm1) = 12gb. Per the previous description, the capacities of both dimm channels are equal.
Summary: Don't move around the preinstalled dimms, just install your new dimms into the empty slots.
the culprit is the way the banks are arranged on the motherboard.....
If the motherboard has two pairs of differently colored DIMM sockets (the colors indicate which bank they belong to, bank 0 or bank 1), then one can place a matched pair of memory modules in bank 0, but a different-capacity pair of modules in bank 1, as long as they are of the same speed. Using this scheme, a pair of 1 GB memory modules in bank 0 and a pair of matched 512 MB modules in bank 1 would be acceptable for dual-channel operation
If Apple uses a motherboard dimm arragement similar to the picture in the wikipedia article you are right, then rearrangement is not necessary.........
Well I received my iMac on Monday, and I put 2 x 8GB Elpida RAM into the 2 empty slots. Didn't change anything else.
Everything works fine. System information says 24 GB, no problems so far.
Oh yes, it works, but you can get approx 10% better performance if you rearrange the modules....
Do the X bench memory test if you don't believe me!
The usual channel/bank designations used by motherboard manufacturers such as Asus are channel A & B, and bank 1 & 2. The order going away from the CPU socket is A1 A2 B1 B2. If you only have two DIMMs they would go in A1 B1, or A2 B2. If you put two DIMMs in A1 A2, they will work, but in single channel mode with a memory bandwidth hit of about 10%, as measured in benchmark tests. In reality this reduction will not be noticeable in normal usage.
If you put a 4GB DIMM in A1 and an 8GB DIMM in A2, they will work in dual channel mode up to 8GB, then in single channel mode from 8GB to 12GB, so unless you're running apps that require more than 8GB there is no memory bandwidth reduction.
The main requirement is that DIMMs must must have the same clock speeds, CAS latencies, and RAM voltages. For the default 2012 27" iMac, these are 1600MHz, a CL latency of 11, and 1.50 volts.
If you install slower RAM, the entire memory will run at the slower speed. If you install 1600MHz RAM with a CL of 10, the entire memory will run at 1333MHz, unless you remove the Apple RAM. Then it will run at 1600MHz with a CL of 10. For maximum compatibility it is recommended that all installed RAM is from the same manufacturer, especially if you use higher performance RAM, such as Corsair Vengeance.
If you put a 4GB DIMM in A1 and an 8GB DIMM in A2, they will work in dual channel mode up to 8GB, then in single channel mode from 8GB to 12GB, so unless you're running apps that require more than 8GB there is no memory bandwidth reduction.
The main requirement is that DIMMs must must have the same clock speeds, CAS latencies, and RAM voltages. For the default 2012 27" iMac, these are 1600MHz, a CL latency of 11, and 1.50 volts.
If you install slower RAM, the entire memory will run at the slower speed. If you install 1600MHz RAM with a CL of 10, the entire memory will run at 1333MHz, unless you remove the Apple RAM. Then it will run at 1600MHz with a CL of 10. For maximum compatibility it is recommended that all installed RAM is from the same manufacturer, especially if you use higher performance RAM, such as Corsair Vengeance.
So in Apple terminology, which is correct?
Bank0/Dimm0 - 4gb
Bank0/Dimm1 - 8gb
Bank1/Dimm0 - 4gb
Bank1/Dimm1 - 8gb
Or
Bank0/Dimm0 - 4gb
Bank0/Dimm1 - 4gb
Bank1/Dimm0 - 8gb
Bank1/Dimm1 - 8gb
Referring to Apple's definition of "Bank", the first configuration would be the best, especially if the 4GB and 8GB are from different manufacturers. It's the same as a standard motherboard DIMM layout. It seems Apple uses "Bank" to refer to the channel, and "Dimm" to refer to the bank. I guess the two channels, ("Banks"), make a single DIMM. This is borne out by my 2010 15" MBP that only has a single dual channel pair labelled as follows:
BANK0/DIMM0
BANK1/DIMM0
If all RAM is fully compatible, the worst that would happen with 4GB and 8GB mixed in the same pair, is that the first 8GB used would be dual channel, the next 4GB would be single channel, followed by another 8GB of dual channel, and a final 4GB of single channel. Any perfomance hit would only be seen in benchmarks, and not in normal use. You'll probably be in the dual channel lower 8GB most of the time.
As a matter of interest, Kingston KTA-MB1600/4G 4GB SODIMMs and KTA-MB1600/8G 8GB SODIMMs most likely use the same Hynix chips as Apple's SODIMMs, and could be rebadged Hynix DIMMs. When I used the Apple compatible Kingston RAM to upgrade my 2010 15" MBP to 8GB, the manufacturer code in System Profiler didn't change - Hynix to Hynix.
As a matter of interest, Kingston KTA-MB1600/4G 4GB SODIMMs and KTA-MB1600/8G 8GB SODIMMs most likely use the same Hynix chips as Apple's SODIMMs, and could be rebadged Hynix DIMMs. When I used the Apple compatible Kingston RAM to upgrade my 2010 15" MBP to 8GB, the manufacturer code in System Profiler didn't change - Hynix to Hynix.[/QUOTE]
Great tip. I was debating which chips to use and my local dealer store stocks Kingston. They cost more than some, but it's obviously good enough for Apple! Thanks.
Great tip. I was debating which chips to use and my local dealer store stocks Kingston. They cost more than some, but it's obviously good enough for Apple! Thanks.
Great tip. I was debating which chips to use and my local dealer store stocks Kingston. They cost more than some, but it's obviously good enough for Apple! Thanks.
[/QUOTE]Just check the chips to make sure they're Hynix. The Hynix modules have 8 small chips on each side.
Just check the chips to make sure they're Hynix. The Hynix modules have 8 small chips on each side.[/QUOTE]
Looking at photos on amazon, these Kingston modules come with either 4 or 8 chips on each side. The 8 chip ones are SO-DIMM - so sould I go for those and assume they are Hynix? Thanks!
Looking at photos on amazon, these Kingston modules come with either 4 or 8 chips on each side. The 8 chip ones are SO-DIMM - so sould I go for those and assume they are Hynix? Thanks!
Looking at photos on amazon, these Kingston modules come with either 4 or 8 chips on each side. The 8 chip ones are SO-DIMM - so sould I go for those and assume they are Hynix? Thanks![/QUOTE]
It turns out they may be either Hynix or Elpida. Elpida is the number three memory chip producer in the world, behind Hynix and Samsung. Elpida is a joint venture with Toshiba, NEC, and Mitsubishi, and has been in operation for over ten years. Either way, you're getting high quality RAM. If the Kingston modules that appear to have four chips on a side have a full length label, they probably have eight to a side. The label makes it appear that there are only four large chips.
I bought a couple of 8GB Kingston SODIMMs yesterday. The 16 chips on each module had Kingston logos, but the chip part numbers were Hynix.
I bought a couple of 8GB Kingston SODIMMs yesterday. The 16 chips on each module had Kingston logos, but the chip part numbers were Hynix.[/QUOTE]
Thanks - did you mix your new eights with the fours in the iMac?
Thanks - did you mix your new eights with the fours in the iMac?
Nope, I always do. But I can't really answer your previous questions. If that came up with mine, I'd take them out, re-install and this persists I would send them back
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Thanks - did you mix your new eights with the fours in the iMac?[/QUOTE]
Apologies for the multi-tag, can't find the answer anywhere and need to install RAM today. Do you install before or after the first boot?