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Old Dec 15, 2012, 12:51 AM   #26
Jazwire
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Originally Posted by tonyep View Post
I'm running 4x 8GB corsair vengeance on mine and it's running at 1600mhz.
Thanks for confirming. Just be running a tad slower till Monday.
(Honestly probably not even notice it.)
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Old Dec 15, 2012, 01:59 AM   #27
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can anyone confirm if adding crucial memory causes it to underclock? I am planning to add 2 x 8gb crucial to the the stock 2 x 4gb from apple to make 24gb total for my incoming 2012 iMac.
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Old Dec 15, 2012, 02:07 AM   #28
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Originally Posted by zarf2007 View Post
can anyone confirm if adding crucial memory causes it to underclock? I am planning to add 2 x 8gb crucial to the the stock 2 x 4gb from apple to make 24gb total for my incoming 2012 iMac.
I want to know this as well, better yet a brand via amazon that works as I got gift cards there.
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Old Dec 15, 2012, 04:36 AM   #29
Overg
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Interesting findings and of the most interesting thread.
Now I wonder what to do? Another cheap apple trick?!
So actually what you say is you need to buy all over again the memory cards, and ditch the apple one.
Btw what brand is apple? Are they manufacturing their own memory?
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Old Dec 15, 2012, 05:37 AM   #30
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Exclamation

Has anybody tested Crucial RAM with the stock Apple RAM do they not underclock together?

I'd appreciate some input as I'm looking to return the Corsair for Crucial if I can through amazon. It is the perfect sweet spot for me 24GB of RAM including Apple's stock.

Last edited by bobright; Dec 15, 2012 at 05:52 AM.
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Old Dec 15, 2012, 05:42 AM   #31
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Would also like to know about Crucial + Apple RAM.

Thumbs up for making this thread.
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Old Dec 15, 2012, 05:59 AM   #32
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The best reason for max the ram!
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Old Dec 15, 2012, 06:07 AM   #33
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Originally Posted by Jazwire View Post
Just got my new 2012 iMac set up, I ordered it with 16 gb (2x8) , and then purchased a Corsair Vengeance Kit from Amazon (the one several people have linked in here) it is 1600mhz ram I'm looking right at the box as I type.

The model number of the ram confirms it is 1600mhz, CMSX16GX3M2A1600C10

But when I go to "About this Mac" it does show correctly 32GB, but it's running at 1333mhz not 1600mhz.

And if I go to Hardware/Memory it shows all 4 sticks running at 1333mhz.


Any ideas???
Edit: Please note that thanks to a user here (Arman) and the iFixit guide, it's been confirmed that the 2012 iMac actually uses 1600 MHz CL11 RAM. At least we know this for the 21.5" model, but considering that Apple would buy this stuff in bulk, it's safe to assume that the 27" will use the same memory. My explanation below is still correct, but it's actually the stock memory that is causing the slow down as experienced by the thread starter and not the other way around, as I had originally presumed. As a general guideline, it best to not mix different latencies and sticks from different manufacturers.


Hi,

Without going too far into the boring technical details that would cause people to fall asleep, you have purchased the wrong RAM.

Take a look at the specifications for a moment...

CMSX16GX3M2A1600C10 - 16GB (2x8GB) Vengeance Performance Memory Kit DDR3 1600MHz CL10

The key part is the last bit (CL10). It means that the RAM has a Column Address Strobe (CAS) latency of 10 (CAS latency is also referred to as CL).

To avoid confusion I have rewritten the post below

The new version:
The iMacs stock RAM has a CL of 11. When you mix sticks with different frequencies weird things happen. To put it very simply: all memory must run at the same CL so the Apple (Hynix) memory is forced to run at CL10, which makes it run at 1333 MHz. When you mix 1333 MHz and 1600 MHz, everything will run at the lowest MHz.


In order to use the stock memory with another kit and still have 1600 MHz memory (not that it really makes a massive difference - the increase in memory will give you far more performance benefits than decreasing the speed of memory from 1600 MHz to 1333 MHz, but I digress), you need a 16 GB 1600 MHz kit with CL 11.

But I would not recommend mixing different brands of RAM, even when they have the exact same specifications anyway.

Quote:
Originally Posted by old post
The iMacs stock RAM has a CL of 9. When you mix sticks with different frequencies weird things happen. To put it very simply: all memory must run at the same CL so the Corsair memory is forced to run at CL9, which makes it run at 1333 MHz. When you mix 1333 MHz and 1600 MHz, everything will run at the lowest MHz.

It's interesting to see though that the iMac is happy with CL10 memory, when it is by itself, and does not clock it back down to CL9, which would make it run at 1333 MHz.

In order to use the stock memory with another kit and still have 1600 MHz memory (not that it really makes a massive difference - the increase in memory will give you far more performance benefits than decreasing the speed of memory from 1600 MHz to 1333 MHz, but I digress), you need a 16 GB 1600 MHz kit with CL 9. Like this:

Kingston KHX16S9P1K2/16 16GB 1600MHz DDR3 Non-ECC CL9 SODIMM HyperX Plug and Play Memory Module (Kit of 2).
When comparing memory sticks that are all clocked at the same MHz, the one with the lowest CL is the best, and the most expensive.
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Last edited by theSeb; Dec 15, 2012 at 11:23 AM. Reason: Added a bit more info
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Old Dec 15, 2012, 06:12 AM   #34
sjz88
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Great Post theSeb! Thanks so much for the info!
So what about the Crucial 16 GB kit?
It doesn't say anything about CL on the description. But I guess Crucial would make it's RAM CL 9, especially since they advertise it as a "2012 27"iMac i7" kit.....
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Old Dec 15, 2012, 06:24 AM   #35
burninggarlic
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Quote:
Originally Posted by theSeb View Post
Hi,

Without going too far into the boring technical details that would cause people to fall asleep, you have purchased the wrong RAM.

Take a look at the specifications for a moment...

CMSX16GX3M2A1600C10 - 16GB (2x8GB) Vengeance Performance Memory Kit DDR3 1600MHz CL10

The key part is the last bit (CL10). It means that the RAM has a Column Address Strobe (CAS) latency of 10 (CAS latency is also referred to as CL).

The iMacs stock RAM has a CL of 9. When you mix sticks with different frequencies weird things happen. To put it very simply: all memory must run at the same CL so the Corsair memory is forced to run at CL9, which makes it run at 1333 MHz. When you mix 1333 MHz and 1600 MHz, everything will run at the lowest MHz.

It's interesting to see though that the iMac is happy with CL10 memory, when it is by itself, and does not clock it back down to CL9, which would make it run at 1333 MHz.

In order to use the stock memory with another kit and still have 1600 MHz memory (not that it really makes a massive difference - the increase in memory will give you far more performance benefits than decreasing the speed of memory from 1600 MHz to 1333 MHz, but I digress), you need a 16 GB 1600 MHz kit with CL 9. Like this:

Kingston KHX16S9P1K2/16 16GB 1600MHz DDR3 Non-ECC CL9 SODIMM HyperX Plug and Play Memory Module (Kit of 2).

When comparing memory sticks that are all clocked at the same MHz, the one with the lowest CL is the best, and the most expensive.
Great post!

I just checked my 2x8GB.

CMSO16GX3M2A1600C11

That probably means CL11.

I probably need to buy another pair to run 1600MHz, right?
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Old Dec 15, 2012, 06:32 AM   #36
sjz88
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I just checked. The Crucial RAM is CL 11!
Guess a lot of people here including me who were going to add 16 GB of Crucial RAM to the 8 GB Apple RAM are pretty fu*ked right now! Haha

Now what is better? To have a combined 24 GB of underclocked RAM or 16 GB crucial RAM at 1600 Mhz?
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Old Dec 15, 2012, 06:37 AM   #37
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Quote:
Originally Posted by theSeb View Post
Hi,

Without going too far into the boring technical details that would cause people to fall asleep, you have purchased the wrong RAM.

Take a look at the specifications for a moment...

CMSX16GX3M2A1600C10 - 16GB (2x8GB) Vengeance Performance Memory Kit DDR3 1600MHz CL10

The key part is the last bit (CL10). It means that the RAM has a Column Address Strobe (CAS) latency of 10 (CAS latency is also referred to as CL).

The iMacs stock RAM has a CL of 9. When you mix sticks with different frequencies weird things happen. To put it very simply: all memory must run at the same CL so the Corsair memory is forced to run at CL9, which makes it run at 1333 MHz. When you mix 1333 MHz and 1600 MHz, everything will run at the lowest MHz.

It's interesting to see though that the iMac is happy with CL10 memory, when it is by itself, and does not clock it back down to CL9, which would make it run at 1333 MHz.

In order to use the stock memory with another kit and still have 1600 MHz memory (not that it really makes a massive difference - the increase in memory will give you far more performance benefits than decreasing the speed of memory from 1600 MHz to 1333 MHz, but I digress), you need a 16 GB 1600 MHz kit with CL 9. Like this:

Kingston KHX16S9P1K2/16 16GB 1600MHz DDR3 Non-ECC CL9 SODIMM HyperX Plug and Play Memory Module (Kit of 2).

When comparing memory sticks that are all clocked at the same MHz, the one with the lowest CL is the best, and the most expensive.
Seb,

Can you help a soon to be Mac owner noob out. I purchased the same RAM as the OP based on many suggestions here. I'm going to return it after reading this thread and realizing its the wrong one. Would something like this work from Crucial (want to use amazon gift card and the Kingston is 32GB)?

http://www.amazon.com/Crucial-PC3-12...ds=Crucial+ram
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Old Dec 15, 2012, 06:58 AM   #38
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Originally Posted by sjz88 View Post
I just checked. The Crucial RAM is CL 11!
Guess a lot of people here including me who were going to add 16 GB of Crucial RAM to the 8 GB Apple RAM are pretty fu*ked right now! Haha

Now what is better? To have a combined 24 GB of underclocked RAM or 16 GB crucial RAM at 1600 Mhz?
If your workflow demands more than 16 GBs of RAM, then having 24 GBs of underclocked RAM will be better than 16 GBs "full speed" RAM. For example I have found in the 2011 Mini with the HD 3000 I can get a couple of extra FPS in games and in GPU benchmarks when I switched from 1333 MHz RAM to 1600 MHz RAM. It's because the integrated graphics processor uses your system RAM and the faster RAM will help it do things quicker, but that use case is not really applicable to the iMac, which has a discrete GPU. Another use case that makes a noticeable difference is when you're zipping and unzipping large archives with WinRar, but how often do you that per day?

Your question is actually best answered by the anandtech review

http://www.anandtech.com/show/6372/m...with-gskill/14
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Old Dec 15, 2012, 06:58 AM   #39
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Has anyone tried the crucial ram with the apple stuff yet? My mac hasn't been processed yet, so still have time to order another 16gb kit from crucial to match it all and maintain the 1600
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Old Dec 15, 2012, 07:04 AM   #40
theSeb
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Originally Posted by burninggarlic View Post
Great post!

I just checked my 2x8GB.

CMSO16GX3M2A1600C11

That probably means CL11.

I probably need to buy another pair to run 1600MHz, right?
Edit: this is all wrong. The CL11 will work perfectly fine. It's the same as the stock memory in the 2012 iMac.



----------

Quote:
Originally Posted by bobright View Post
Seb,

Can you help a soon to be Mac owner noob out. I purchased the same RAM as the OP based on many suggestions here. I'm going to return it after reading this thread and realizing its the wrong one. Would something like this work from Crucial (want to use amazon gift card and the Kingston is 32GB)?

http://www.amazon.com/Crucial-PC3-12...ds=Crucial+ram
Edit:

It will work just fine.
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Last edited by theSeb; Dec 15, 2012 at 11:21 AM.
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Old Dec 15, 2012, 07:06 AM   #41
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I cannot say for sure, because I don't know how the 2012 iMac will handle CL11 memory at this early point in time. But, I would say that I would not recommend using that memory at all, even if it runs ok. You have basically bought the cheapest and thinnest tyres for your brand new BMW M3.
Are there any potential risks with using this memory anyway?
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Old Dec 15, 2012, 07:10 AM   #42
burninggarlic
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Quote:
Originally Posted by theSeb View Post
If your workflow demands more than 16 GBs of RAM, then having 24 GBs of underclocked RAM will be better than 16 GBs "full speed" RAM. For example I have found in the 2011 Mini with the HD 3000 I can get a couple of extra FPS in games and in GPU benchmarks when I switched from 1333 MHz RAM to 1600 MHz RAM. It's because the integrated graphics processor uses your system RAM and the faster RAM will help it do things quicker, but that use case is not really applicable to the iMac, which has a discrete GPU. Another use case that makes a noticeable difference is when you're zipping and unzipping large archives with WinRar, but how often do you that per day?

Your question is actually best answered by the anandtech review

http://www.anandtech.com/show/6372/m...with-gskill/14
Thank you!

I also got some info from my friends. One says I can install windows and reset it with SPD tool. Another says I might possibly change the settings in smbios.

Are they correct?
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Old Dec 15, 2012, 07:18 AM   #43
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Are there any potential risks with using this memory anyway?
From a physical damage point of view, no there are no risks. But it might simply not work or it may have stability issues under certain workloads.

Bear in mind how this stuff is produced, via a process called binning.

http://en.wikipedia.org/wiki/Product_binning

Quote:
Semiconductor manufacturing is an imprecise process, achieving as low as 30% for yields.[2] Defects in manufacturing are not always fatal though, in many cases it is possible to salvage a part by trading off performance characteristics. For example, reducing its clock frequency or disabling non-critical parts that are defective, their performance level can be marked down accordingly and sold at a lower price, fulfilling the needs of lower-end market segments.
This practice occurs throughout the semiconductor industry on products such as CPUs, RAM and GPUs.
So basically at the factory there will be a bunch of people dressed in sci-fi looking white coats walking around with clipboards and testing these components batch by batch. Here are some of the typical conversations that I envisage:

"Ahh, this batch is awesome. It runs stable at 1600 MHz using CL 9. Brilliant, this will go into our 'Super Awesome Extra Fast Destroyer' product line"

"Hmm, these ones are not so great. They can only do 1600 MHz at CL11. Let's whack these into our value products"

Edit: And unfortunately that's exactly what Apple bought. The value line.
----------

Quote:
Originally Posted by burninggarlic View Post
Thank you!

I also got some info from my friends. One says I can install windows and reset it with SPD tool. Another says I might possibly change the settings in smbios.

Are they correct?
Using something like an SPD tool is asking for instability troubles, in my opinion. Bear in mind that a Mac is not like a Windows PC. There is no BIOS to go into and change the speeds of the memory.
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Last edited by theSeb; Dec 15, 2012 at 11:22 AM.
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Old Dec 15, 2012, 07:37 AM   #44
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Bear in mind that a Mac is not like a Windows PC. There is no BIOS to go into and change the speeds of the memory.
What does Windows have to do with BIOS?
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Old Dec 15, 2012, 07:41 AM   #45
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What does Windows have to do with BIOS?
PCs (regardless of what operating system they are running) allow access to the BIOS (or more recently EFI). Macs do not allow access to the EFI. I specifically mentioned Windows because it was in the context of the post that I replied to. What is confusing you?
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Old Dec 15, 2012, 07:52 AM   #46
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PCs (regardless of what operating system they are running) allow access to the BIOS (or more recently EFI). Macs do not allow access to the EFI. I specifically mentioned Windows because it was in the context of the post that I replied to. What is confusing you?
This smbios was what I meant.
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Old Dec 15, 2012, 07:53 AM   #47
Richard Peters
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I cannot say for sure, because I don't know how the 2012 iMac will handle CL11 memory at this early point in time. But, I would say that I would not recommend using that memory at all, even if it runs ok. You have basically bought the cheapest and thinnest tyres for your brand new BMW M3.

----------



It is interesting that Crucial claims CL11 is compatible with a Mac. As I just posted, I cannot say for sure how well it will run in a 2012 iMac. It may run just fine, but you cannot mix it with the stock RAM and expect all sticks to run at 1600 MHz
Ah! I have the Crucial ram waiting to go in my iMac when it arrives. Would I be better off with something like this instead then?
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Old Dec 15, 2012, 07:58 AM   #48
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Ah! I have the Crucial ram waiting to go in my iMac when it arrives. Would I be better off with something like this instead then?
If you read the thread from the start, you'll see it was a vengeance kit mixed with the stock apple ram that highlighted this issue.
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Old Dec 15, 2012, 07:58 AM   #49
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Mixing memories with different CAS latencies can cause issues because of RAM timings. This is why you should buy all the RAM you need from one vendor and in one go. Vendors can switch chips or even brands in the future. This includes Apple, so who knows what the January 2013 iMacs will have.

Assigning semiconductor components from a single batch to different products to increase the net yield is done at every level in your new iMAC or any other piece of electronics out there. CPU, GPU, screen, chipset etc.

CL11 RAM is not inferior, it just runs at a slower timing. CL10 or CL11 is not the same difference as 1600 vs 1333MHz! You could even argue that CL10 runs at a way more critical timing and therefore is more likely to cause problems.

And to the original poster: if you google the part number of the memory module that you can see on the photos on the iMac iFixit page, you'll see that iMac stock RAM is actually specced at CL11 @ 1600MHz. Now check the timing tables of your new memory. I'm pretty sure you will see why combining the two different chips together will result in them running at 1300MHz, as that most likely is the only compatible setting between the two different brands.
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Old Dec 15, 2012, 08:04 AM   #50
Richard Peters
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If you read the thread from the start, you'll see it was a vengeance kit mixed with the stock apple ram that highlighted this issue.
Sorry yes, I didn't make myself clear there. I've got 32gb ram sitting here that's CL11, so I was wondering if I should swap that for something that's CL10. Going off on a slight tangent from the original thread topic, apologies
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