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Old Jan 16, 2013, 10:32 AM   #76
drambuie
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Quote:
Originally Posted by Confuzzzed View Post
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

----------





Thanks - did you mix your new eights with the fours in the iMac?

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?[/QUOTE]

If by "first boot" you mean the first startup after unpacking the iMac, yes you should always run it before making any mods to make sure it's problem free from the factory. Then you can make changes. Otherwise, if there's a problem, you won't know if it was a factory problem, or something you did.
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Old Jan 16, 2013, 10:43 AM   #77
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Quote:
Originally Posted by drambuie View Post
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?
If by "first boot" you mean the first startup after unpacking the iMac, yes you should always run it before making any mods to make sure it's problem free from the factory. Then you can make changes. Otherwise, if there's a problem, you won't know if it was a factory problem, or something you did.[/QUOTE]

Thank you. That is indeed what I meant, have read elsewhere that is best to install before first start-up but what you say makes sense
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Old Jan 16, 2013, 12:01 PM   #78
WilliamDu
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RAM/slot configuration for 24GB

Following from Crucial tech support:

Apple installs the two 4G sticks in the slots the processor accesses first for RAM.

Crucial recommends removing the two 4GB sticks and replacing with their two 8GB sticks, then installing the original two 4GB sticks in the remaining two empty slots.

Don't shoot the messenger. Hopefully Applecare will know after I call them with the serial number of my 27" scheduled for delivery tomorrow afternoon

In any case, make sure the thing works as is before messing with the RAM.

Additional edit info:
Preceding confirmed several hours later by Apple Support technical support advisor.

Apple also recommends remove their two 4GB sticks, replace with the two new 8GBs, then install the Apple sticks in the remaining empties.

Last edited by WilliamDu; Jan 16, 2013 at 01:38 PM. Reason: Additional facts to add.
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Old Jan 16, 2013, 12:19 PM   #79
drambuie
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Quote:
Originally Posted by WilliamDu View Post
Following from Crucial tech support:

Apple installs the two 4G sticks in the slots the processor accesses first for RAM.

Crucial recommends removing the two 4GB sticks and replacing with their two 8GB sticks, then installing the original two 4GB sticks in the remaining two empty slots.

Don't shoot the messenger. Hopefully Applecare will know after I call them with the serial number of my 27" scheduled for delivery tomorrow afternoon

In any case, make sure the thing works as is before messing with the RAM.
Either way, it really doesn't make a whole lot of difference. In the default configuration with 2x8GB added to the empty slots, bank switching will occur after you use all 8BG. If you do the Crucial recommended swap, band switching will occur after 16GB is filled. The bank switching is done by the memory controller logic, and doesn't cause any performance hit.

I guess Crucial's suggestion ensure's that you have consistent performance for the first 16GB. It would also be a good test of the added RAM during the return period, as it would probably be rarely used in the higher addresses of upper bank.
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Old Jan 16, 2013, 01:42 PM   #80
WilliamDu
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Smile Apple confirmation on RAM configuration.

Quote:
Originally Posted by drambuie View Post
Either way, it really doesn't make a whole lot of difference. In the default configuration with 2x8GB added to the empty slots, bank switching will occur after you use all 8BG. If you do the Crucial recommended swap, band switching will occur after 16GB is filled. The bank switching is done by the memory controller logic, and doesn't cause any performance hit.

I guess Crucial's suggestion ensure's that you have consistent performance for the first 16GB. It would also be a good test of the added RAM during the return period, as it would probably be rarely used in the higher addresses of upper bank.
Thanks drambuie (Excellent aperitif by the way),
After several days of hold music, finally got an Apple tech guy on the phone that understood the question and he confirmed Crucial's recommendation.
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Old Jan 16, 2013, 03:53 PM   #81
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Quote:
Originally Posted by drambuie View Post
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?
If by "first boot" you mean the first startup after unpacking the iMac, yes you should always run it before making any mods to make sure it's problem free from the factory. Then you can make changes. Otherwise, if there's a problem, you won't know if it was a factory problem, or something you did.[/QUOTE]

I was going to install my ram before the very first bootup, but I will follow your advice and set the iMac up first to ensure its working OK, then I'll install the ram later. Thanks
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Old Jan 16, 2013, 03:56 PM   #82
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Quote:
Originally Posted by Fatboy71 View Post
If by "first boot" you mean the first startup after unpacking the iMac, yes you should always run it before making any mods to make sure it's problem free from the factory. Then you can make changes. Otherwise, if there's a problem, you won't know if it was a factory problem, or something you did.
I was going to install my ram before the very first bootup, but I will follow your advice and set the iMac up first to ensure its working OK, then I'll install the ram later. Thanks [/QUOTE]


Any advances on this? Going, going...gone
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Old Jan 16, 2013, 04:06 PM   #83
Fatboy71
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Quote:
Originally Posted by WilliamDu View Post
Following from Crucial tech support:

Apple installs the two 4G sticks in the slots the processor accesses first for RAM.

Crucial recommends removing the two 4GB sticks and replacing with their two 8GB sticks, then installing the original two 4GB sticks in the remaining two empty slots.

Don't shoot the messenger. Hopefully Applecare will know after I call them with the serial number of my 27" scheduled for delivery tomorrow afternoon

In any case, make sure the thing works as is before messing with the RAM.

Additional edit info:
Preceding confirmed several hours later by Apple Support technical support advisor.

Apple also recommends remove their two 4GB sticks, replace with the two new 8GBs, then install the Apple sticks in the remaining empties.
Thanks for the excellent advice. I was wondering myself if the purchased ram should just be inserted in the empty slots, but now that you've had the same information told to you from both Crucial and Apple, I think I'll follow that advice, thanks for updating its much appreciated

----------

Quote:
Originally Posted by Confuzzzed View Post
I was going to install my ram before the very first bootup, but I will follow your advice and set the iMac up first to ensure its working OK, then I'll install the ram later. Thanks

Any advances on this? Going, going...gone[/QUOTE]


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Old Jan 18, 2013, 02:41 AM   #84
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Quote:
Originally Posted by Fatboy71 View Post
I was going to install my ram before the very first bootup, but I will follow your advice and set the iMac up first to ensure its working OK, then I'll install the ram later. Thanks
This is what I did last night, didn't go through all the screen tests or image retention thing but made sure the machine worked ok and then popped the new RAM in, switching them round with where the stock Apple ones (Elpida if it helps anyone) were sitting (slots 1 & 3). Worked fine.
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Old Jan 19, 2013, 04:12 PM   #85
Ambulater
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16gb

So I figured I'd start by adding just one 8GB stick from Crucial (for 16GB total) and see what my memory usage looks like under load. I simply inserted the 8GB stick in the first empty slot leaving the preinstalled Apple sticks where they were at by default. This resulted in the following config:

Slot 4: Empty
Slot 3: 4GB (Apple)
Slot 2: 8GB (Crucial)
Slot 1: 4GB (Apple)

In this configuration the iMac would not boot and only gave error beeps when power was pressed. So I rearranged as follows:

Slot 4: Empty
Slot 3: 8GB (Crucial)
Slot 2: 4GB (Apple)
Slot 1: 4GB (Apple)

The iMac now boots just fine and reports 16GB of RAM. Can anyone explain why the first configuration fails to boot?
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Old Jan 19, 2013, 06:36 PM   #86
digitalfailure
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I must admit, I never even turned my machine on before installing the extra 2x8gb sticks of crucial. Just popped the cover off and inserted the sticks into the 2 empty slots and fired it up. It reported 24gb @1600 ok.
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Old Jan 20, 2013, 02:53 AM   #87
Confuzzzed
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Quote:
Originally Posted by Ambulater View Post
So I figured I'd start by adding just one 8GB stick from Crucial (for 16GB total) and see what my memory usage looks like under load. I simply inserted the 8GB stick in the first empty slot leaving the preinstalled Apple sticks where they were at by default. This resulted in the following config:

Slot 4: Empty
Slot 3: 4GB (Apple)
Slot 2: 8GB (Crucial)
Slot 1: 4GB (Apple)

In this configuration the iMac would not boot and only gave error beeps when power was pressed. So I rearranged as follows:

Slot 4: Empty
Slot 3: 8GB (Crucial)
Slot 2: 4GB (Apple)
Slot 1: 4GB (Apple)

The iMac now boots just fine and reports 16GB of RAM. Can anyone explain why the first configuration fails to boot?
The additional stick wasn't pressed in properly most likely. I think
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Old Jan 20, 2013, 06:29 AM   #88
dearlaserworks
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Quote:
Originally Posted by Confuzzzed View Post
The additional stick wasn't pressed in properly most likely. I think
Agree. I am running fine in the first config, single Crucial 8GB stick in the lower of two free slots. And I powered up and verified the system worked as shipped before popping open the RAM door to make even the simplest of changes. It only took a few extra minutes and ensured a little sanity if anything didn't go smoothly with the memory install.
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Old Jan 20, 2013, 08:10 AM   #89
dubmick
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I've just this week upgraded my 2011 27" i5 iMac from 4gb to 16gb. It now runs like a dream after a year of me complaining about the performance of the machine. It is quite clear to me that Apple under powered this machine in the ram department. Activity monitor states that I am using 7-8 gb of ram when running my usual apps. Quite annoying from Apple considering the cost of an iMac. Delighted it is running so well now though.
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Old Jan 21, 2013, 05:21 AM   #90
lixuelai
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Quote:
Originally Posted by roverma View Post
Wrong, for correct dual channel operation you have to install 2x4 in one channel and the 2x8 in the other channel!
Come on think for a second... The basis for dual channel memory is 2 memory channels that can be simultaneously accessed by the CPU therefore doubling the throughput. Logically for the best performance you want to have the same amount of memory in each channel. I intentionally only stated 12GB in each channel because I did not know the exact memory bank config of the iMac at the time of post. But what I stated is 100% accurate. Anyway you are welcome to prove me wrong by trying it in different ways but this is like Memory 101 in DIY PC forums.

Quote:
Originally Posted by SDDave2007 View Post
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.
See above.

Quote:
Originally Posted by Ambulater View Post
So I figured I'd start by adding just one 8GB stick from Crucial (for 16GB total) and see what my memory usage looks like under load. I simply inserted the 8GB stick in the first empty slot leaving the preinstalled Apple sticks where they were at by default. This resulted in the following config:

Slot 4: Empty
Slot 3: 4GB (Apple)
Slot 2: 8GB (Crucial)
Slot 1: 4GB (Apple)

In this configuration the iMac would not boot and only gave error beeps when power was pressed. So I rearranged as follows:

Slot 4: Empty
Slot 3: 8GB (Crucial)
Slot 2: 4GB (Apple)
Slot 1: 4GB (Apple)

The iMac now boots just fine and reports 16GB of RAM. Can anyone explain why the first configuration fails to boot?
Honestly I don't see why the first config didn't work. But it can be because of the memory channel configuration. In the original config you had 4GB in 1st channel and 12GB in the 2nd channel while for the working config you have 8GB in both channels. You should run a utility to see if you are getting synchronous dual channel in the working config. Something like CPU-Z under Windows. It would be interesting if you are indeed getting full synchronous dual channel as that would mean it is only matching size in channel configuration that matters.

Last edited by lixuelai; Jan 21, 2013 at 07:26 AM.
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Old Jan 21, 2013, 05:38 AM   #91
faneos
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Originally Posted by rick.m650 View Post
I don't see why no one in this forum intends to add 2 x 8GB chips and keep using the 2 x 4GB chips that come with the iMac. Waste not want not... is there a problem with running 24 GB?
You don't need it boy.
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Old Jan 21, 2013, 12:47 PM   #92
Confuzzzed
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Originally Posted by rick.m650 View Post
I don't see why no one in this forum intends to add 2 x 8GB chips and keep using the 2 x 4GB chips that come with the iMac. Waste not want not... is there a problem with running 24 GB?
I think this is precisely what EVERYONE on this thread is doing. And it works fine. And some excellent detective work and advice has come about from contributors on the thread with regards what sticks to insert where
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Old Jan 25, 2013, 10:42 PM   #93
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Not to beat a dead horse here, but I've seen conflicting info across the web on how to arrange a ram upgrade on the 27." I purchased 16 GB of Crucial ram, removed the stock ram, inserted the crucial ram in its place, and then installed the stock ram (in what were originally empty slots).

Can anyone knowledgeable please confirm that the resulting config is correct for max 24 GB performance?:



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Old Jan 25, 2013, 11:38 PM   #94
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Quote:
Originally Posted by surripere View Post
Can anyone knowledgeable please confirm that the resulting config is correct for max 24 GB performance?:
Do an Xbench memory test with your system. Then rearrange the memory, so the 8GB sticks are in the same lowest bank and the 4GB in the highest bank.
Like this:
Bank 0/dimm0 8 GB
Bank 1/dimm0 4 GB
Bank 0/dimm1 8 GB
Bank 1/dimm1 4 Gb

And do the test again. It should give faster results.
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Old Jan 26, 2013, 12:40 AM   #95
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I appreciate the feedback, Gogol. Your response seemingly contradicts a few others in this thread, so I'm not entirely certain who to believe at this point (see below).

I'm guessing xbench should confirm your response, but does xbench even run on Mountain Lion?

Quote:
Originally Posted by nosnhojm View Post
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

Quote:
Originally Posted by drambuie View Post
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.
Quote:
Originally Posted by WilliamDu View Post
Following from Crucial tech support:

Apple installs the two 4G sticks in the slots the processor accesses first for RAM.

Crucial recommends removing the two 4GB sticks and replacing with their two 8GB sticks, then installing the original two 4GB sticks in the remaining two empty slots.

Don't shoot the messenger. Hopefully Applecare will know after I call them with the serial number of my 27" scheduled for delivery tomorrow afternoon

In any case, make sure the thing works as is before messing with the RAM.

Additional edit info:
Preceding confirmed several hours later by Apple Support technical support advisor.

Apple also recommends remove their two 4GB sticks, replace with the two new 8GBs, then install the Apple sticks in the remaining empties.
Quote:
Originally Posted by Gogol View Post
Do an Xbench memory test with your system. Then rearrange the memory, so the 8GB sticks are in the same lowest bank and the 4GB in the highest bank.
Like this:
Bank 0/dimm0 8 GB
Bank 1/dimm0 4 GB
Bank 0/dimm1 8 GB
Bank 1/dimm1 4 Gb

And do the test again. It should give faster results.
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Old Jan 26, 2013, 01:50 AM   #96
Fatboy71
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Quote:
Originally Posted by surripere View Post
Not to beat a dead horse here, but I've seen conflicting info across the web on how to arrange a ram upgrade on the 27." I purchased 16 GB of Crucial ram, removed the stock ram, inserted the crucial ram in its place, and then installed the stock ram (in what were originally empty slots).

Can anyone knowledgeable please confirm that the resulting config is correct for max 24 GB performance?:

Image

Image


I done it the way this post mentions and everything works fine, Memtest tests were passed:

http://forums.macrumors.com/showpost...8&postcount=78

If both Apple & Crucial recommends the same, then that's good enough reason to go with it
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Old Jan 27, 2013, 09:00 AM   #97
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We need a dedicated benchmarker to review the real impact of the various configurations


I would do it but I do not have my new 27" yet !
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Old Feb 3, 2013, 07:44 PM   #98
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Quote:
Originally Posted by surripere View Post
I appreciate the feedback, Gogol. Your response seemingly contradicts a few others in this thread, so I'm not entirely certain who to believe at this point (see below).

I'm guessing xbench should confirm your response, but does xbench even run on Mountain Lion?
Xbench 1.3 runs on Mountain Lion, just don't do the thread test.

I have tested with original 8GB RAM and two 8GB sticks Kingston KTA in the empty slots. After that i rearranged the memory as in my post and it was 10% faster. People have to test for themselves, but this was my experience.
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Old Feb 13, 2013, 03:57 PM   #99
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Exclamation

Oh dear lord...so much confusion.

When you stop and look at the setup, it makes sense.

Bank and Channel are intermixable terms...they both refer to one grouping of memory accessible in parallel with the right setup.

DIMM refers exactly to what it says...the DIMM itself (or the chip or the slot), which is the physical piece of hardware.

Bank 0/dimm0 - First Channel, First RAM Chip
Bank 1/dimm0 - Second Channel, First RAM Chip
Bank 0/dimm1 - First Channel, Second RAM Chip
Bank 1/dimm1 - Second Channel, Second RAM Chip

This is how it's ALWAYS been setup on motherboards in the last several years since Dual Channel (and now Tripple Channel) operation was first introduced. Every motherboard interleaves channels slot to slot. If the first slot on the motherboard is channel 0 the second slot is ALWAYS channel 1. If your board runs dual channel memory, then you typically have 4 or 8 slots for memory and it will run channel: 0, 1, 0, 1 (for 4 slots) or 0, 1, 0, 1, 0, 1, 0, 1 (For 8 Slots). If your board supports tripple channel memory (Hello Apple welcome to 2010) then you typically have 6 or 12 DIMM slots on the board and they run the following channel layout: 0, 1, 2, 0, 1, 2 (for 6) or 0, 1, 2, 0, 1, 2, 0, 1, 2 (for 12).

As such, what Gogol is posting is absolutely correct. It's 8, 4, 8, 4 or 4, 8, 4, 8 as the correct config, NOT 8, 8, 4, 4 or 4, 4, 8, 8 which would produce a single channel setup. Crucial recommends the 8, 4, 8, 4 configuration (confrmed by Apple according to earlier posts in the thread) because it allows the larger of the two sets of dual channeled memory to be accessed first...limiting any potential cross manufacturer issues till you get beyond 16G of memory used.

To maximize your performance put MATCHING DIMMs into DIMM0 and DIMM1 (or DIMM0, 1 and 2) of a given "Bank" (Channel). DIMMS in Channel 0 and Channel 1/2 do NOT need to match or even be of the same size, so long as DIMM0 and DIMM1 (And DIMM2 for tripple channel) of each channel are identical.

HOWEVER every DIMM in ANY SLOT in ANY CHANNEL must be the same type (DDR3, failing this it won't work at all and will probably destroy the RAM chips and maybe the slots), speed of DIMM (PC3-12800/DDR3-1600), and CAS Latency (CL=11). Changing any of these causes the ENTIRE MEMORY LAYOUT to support only the SLOWEST speed available. (Placing a single PC3-10800 DIMM into a set of 8 slots all the rest filled with PC3-12800 RAM will cause the PC to work at PC3-10800 speed).

Many people will tell you that putting the same TYPE (manufacturer, brand, etc.) of RAM in all channels increases speeds or stability. That may be the case and it certainly won't hurt. But so long as you're using high quality RAM keeping the manufacturers the same shouldn't be an issue.

Another "Best Practice" is to purchase the RAM "Kits" from a given high quality manufacturer instead of seperate RAM chips. KITS are specifically put together by the manufacturers from the same "run" of the same chips. By installing "Kits" (the 2x4 or 2x8 you see sold on sites like Crucial or Corsair) you are not only guaranteeing the same chips, you're also guaranteeing the same COMPONENTS on those chips and the same conditions under which those chips where produced. When you go to, say, Crucial and buy two separate 8G Ram Chips, you are not guaranteed to get two RAM chips from the same run. One chip may be signficantly older than the other (wear issues), one chip may have different internal compoents (capactors, resistors, even the silicon for the board may be different), or even one of the two chips may have been manufactured in different plants under VASTLY different conditions. Buying "Kitted" RAM (supposedly) removes these kinds of potential differences.

The second major misunderstanding I've seen posted on this thread is summed up well by the following:

Quote:
"Come on think for a second... The basis for dual channel memory is 2 memory channels that can be simultaneously accessed by the CPU therefore doubling the throughput."
Sir, I don't think you quite understand what dual channel RAM actually means. No offense intended, but your understanding seems flawed by what I'm reading from you.

Dual Channel does not mean that the RAM ACROSS CHANNELS is accessed in parallel, it means that the ram WITHIN THE SAME CHANNEL is accessed in parallel.

Your suggestion to make sure to keep the RAM in both channels the same leads me to believe that you feel that 12G in Channel 0 and 12G in Channel 1 would allow the PC to Dual Channel 12G of memory. This is incorrect and a flawed understanding (again, no offence intended). Only the RAM within a given channel can be accessed in parallel, thus the 2x4 in a Channel and 2x8 in another Channel is the right configuration, not 8+4 in Channel 0 and 8+4 in Channel 1.

--Illydth
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Old Feb 13, 2013, 05:09 PM   #100
lixuelai
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Quote:
Originally Posted by Illydth View Post
snip
You are confused because Apple displays the memory config rather badly in System Profiler. It is true that Intel has had the same memory config since P4. So the easiest way I can convince you is to pull up a motherboard manual.

http://vfiles.cizgi.com.tr/cizgi/pms...hdeluxe_en.pdf

Page 2-14.

This is just one I know on top of my head is very clear about memory installation. You can check other motherboard manuals as well and they will be the same.

Now what Apple did was rearrange the order the slots are displayed in System Profiler. To give you an example 16GB of RAM in a 4 slot system will be seen like this:

bank 0/dimm0 - 8GB
bank 1/dimm0 - 8GB
bank 0/dimm1 - empty
bank 1/dimm1 - empty

In reality on a 2012 iMac the slots are 8/_/8/_ if you are to look at how the memory is installed. That is where the confusion lies.
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