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More RAM or less, tri channel RAM?

M

mjsmke

macrumors 6502a
Original poster
I am currently using 12GB (3 x 4GB) in Photoshop. I only max out the RAM when using other apps an/or working with lots of big files. This only happens once every 2 weeks.

I have a spare 2GB stick. Is it worth installing this in the 4th slot? Am i right in thinking i will still benefit from tri channel memory until the first 3 sticks are full?

Or, would i be better off sticking with the current 12GB and using a partition of a RAID0 volume i plan to install?

Thanks in advance
 
i would suggest sticking with your current setup, installing that 2gb stick would ruin your setup.
 
Thank for the replies. I'll stick with what i have. I'm planning on getting an SSD and RAID0 setup soon anyway so that will help.
 
I am actually considering this exact same situation...heh.

The research that I did when I was buying my Mac Pro indicated that the memory controller for the Nehalem's works like you were saying. In a 4-slot configuration the first three slots are treated as triple channel, and the 4th is treated as single channel. This has to do with the bandwidth of the overall memory controller, it simply can't handle two triple channel pipelines at once. So basically if you install 3x4GB sticks and 1x2GB stick then you'll have 3x bandwidth to the 12GB, and 1x bandwidth to the 2GB.

What is not clear to me is how the controller actually allocates storage between the sticks. At first I thought that it would simply fill up the 12GB first, and then move on to the 2...which you'd think would be fine. You'd get excellent performance from your RAM until you filled it up, and then you'd get slightly less performance for that last 2GB. But I haven't actually read anywhere that it works that way. For all I know it could use the 2GB first, in the worst case, or even evenly across the rest of the system. If it does work that way it could hurt performance, but to be honest I am not totally sure.

It's also worth pointing out that in tests done between triple channel and dual channel configurations that triple channel wins...but barely. As in the difference doesn't really even matter. Single would obviously be more of a difference though.

One thing is clear though: disk access is far worse than single channel RAM performance. So overall, if you're maxing out your RAM, I think this configuration could be worth testing out.

So to answer your question, I think I can mostly validate your assumptions...but I am not totally sure of the end result. I actually came here to post today to ask the exact same question, because I am not totally sure. I get my 3x4GB sticks in the mail today, so I may very well try it out later, and if I do i'll try to post my findings. But if there's anyone out there that does actually KNOW whether or not this would be advantageous...please let us know 🙂
 
the advantages of dual/triple channel are so minuscule in real-world use that they're not worth thinking about. if the 2GB is compatible with the DIMMs you're using, then just use the fourth slot. swapping to disk is much worse than the slowest RAM out there.
 
Well I installed my RAM last night and everything seems to be working just fine. I ordered 3x4GB sticks from OWC for my new 2010 Mac Pro 3.2GHz, which came stock with 3x1GB sticks from Apple.

What I did was pull the original sticks, and install the new 3 in the first three slots. Then I installed one of the old 1GB sticks in the 4th slot. I powered it up, got the "Ram Modules installed in the recommended locations" message, and was a happy camper.

Further checking revealed 13GB of RAM in the About This Mac window and in System Profiler.

Then I did some stress testing. I fired up all my daily apps...Safari, Mail, iCal, iTunes, Adium, Transmit, Xcode, and a few others. I started up World of Warcraft for good measure, and left that sitting idle. Then I started Aperture and actually did a little editing work. By now I was down to about 3-4GB of free RAM. I wanted to max it out, so I started Photoshop and started a Photomerge operation to create a panarama. With 20 pictures the panarama finished quickly, but it was enough to max out the RAM.

While it was in this state I tested everything out. All the other programs seemed fine, Aperture performed well. Even World of Warcraft was pushing 200 FPS while all this was going on. When the panarama finished aligning and blending it looked good and was very responsive to zoom in and look around on.

So in conclusion I believe that everything here works as we expected. You most likely get triple channel performance from the 12GB, and single channel from the 1 or 2GB at the end. That being said, this is obviously not a scientific test. I didn't do any memory read/write tests or anything like that. But in a real world usage scenario, I don't see why adding that 4th stick will do you any harm whatsoever.
 
cutterman said:
I use a 4-4-2-2 configuration and it works fine. It is the 8GB (registered) sticks that cant be mixed with 4 and 2GB ones.
Click to expand...

I'm running a 4-4-1-1 config with the 1's being the stock Apple ram that came with the machine, and the 4's being KVR1333D3E9SK2/8G which are ECC unbuffered with thermal sensor.

I went with buying the 8Gb KVR kit for only $165.99 USD, and got 10Gb dual channel. I could have gotten 3x4Gb and get 12Gb triple channel, but that would have cost $320 USD from OWC which is almost 100% more than the cost I spent, but only 20% more memory from what I have. Some people don't like KVR ram because it's not "Guaranteed" but it is the exact same product, but hasn't been individually tested to work in the Mac Pro but still has the same lifetime warranty.

I just tested my RAM last night using memtest (http://www.command-tab.com/2008/01/11/how-to-test-ram-under-mac-os-x/) Ran perfectly after about 2 hours and no errors at all. Seems like the KVR ram I got was perfect! If I find I'm needing more RAM in the future, I can add it as needed pulling the stock Apple ram.
 
Ive still got 3x 2 GB sticks left over from the 12GB upgrade so i'll put one of those in the 4th slot.

Thanks for all the recommendations and info. 🙂
 
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This is excellent news indeed. I'm glad you guys were able to test it out and it works.

Now what do you guys thinking of purchasing one stick of 8 GB of RAM and mixing it with my stock 3x1 GB for a total of 11 GB? think this will work as well?
 
Icaras said:
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This is excellent news indeed. I'm glad you guys were able to test it out and it works.

Now what do you guys thinking of purchasing one stick of 8 GB of RAM and mixing it with my stock 3x1 GB for a total of 11 GB? think this will work as well?
Click to expand...

not if the 8gb is ecc and reg.
 
Icaras said:
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This is excellent news indeed. I'm glad you guys were able to test it out and it works.

Now what do you guys thinking of purchasing one stick of 8 GB of RAM and mixing it with my stock 3x1 GB for a total of 11 GB? think this will work as well?
Click to expand...

8Gb sticks don't work with anything except 8Gb sticks. I'm not sure if only one will work by itself, but 2x8Gb, 3x8Gb and 4x8Gb will work if they are all the same. You can mix 1Gb, 2Gb, and 4Gb sticks together, but if you are planning on using the 1Gb sticks that come from apple, you need to make sure that the ram you mix with it is unbuffered, otherwise they won't work together. When you are mixing non-8Gb sticks, try to do it in pairs so that they will work in dual-channel mode. I'm skeptical about anyone running just one stick that isn't the same, but I guess I could test it out on my rig by doing a 1-1-1-2 config. I'll have to try that out sometime.
 
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Thanks for that. Yea, actually I do recall someone clarifying the deal with 8 GB DIMMs here but i forgot. Yes, please do share if you get a chance to test that config out.
 
I got curious, and ran several different configurations. If I installed a configuration that wasn't optimal, it displayed the following message that showed the correct config, but in all cases, showed the correct amount of RAM in the system.

Below were the tests I ran. When it did not work, it only showed the attached message once the computer started up (good thing I have a SSD otherwise this would have taken much longer). Since all of my ram was unbuffered (all the same) they worked. If I had mixed unbuffered/buffered/registered Ram, the computer would not start up and a light would flash saying that the ram is incompatible together.

Below, the slots are the same as numbered on the processor board, and worked showed that the Ram was installed properly, not worked showed the attached message suggesting the correct configuration.

Slot 1 - Slot 2 - Slot 3 - Slot 4 - worked
1-1-1-0 Yes
0-1-1-1 No
1-1-1-4 No
1-1-4-1 No
1-4-1-1 Yes
4-1-1-1 Yes
4-4-1-1 Yes
1-1-4-4 Yes
1-4-1-4 No
4-1-1-4 No
1-4-4-1 No

I have mine left as 4-4-1-1 which was the recommended configuration. I'm sure that these configurations would be the same for mixing and 1Gb, 2Gb, or 4Gb combinations, but 8Gb sticks don't work with anything other than 8Gb sticks.
 

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The weirdest one to me is why 1-1-1-4 doesn't work, and why it recommends 1-4-1-1. That's like the complete opposite of what I would have expected.
 
Forgive the newbie question, but in my 1st gen Mac Pro (1,1) I have the stock apple 512's in the first two slots, and 1GB in the next 4.
Was going to add either 2x2GB or maybe 2x4GB - wondering whether I should pull the 512s and add the new RAM there, or what.
Reading a little about tri channel, wondering if it applies to my machine.
thanks!
 
c23roo said:
Forgive the newbie question, but in my 1st gen Mac Pro (1,1) I have the stock apple 512's in the first two slots, and 1GB in the next 4.
Was going to add either 2x2GB or maybe 2x4GB - wondering whether I should pull the 512s and add the new RAM there, or what.
Reading a little about tri channel, wondering if it applies to my machine.
thanks!
Click to expand...

No triple channel in anythin other than 2009 and 2010 MP

For MP 1,1 only matched pairs
from Mactracker app:

Maximum RAM: 32 GB (Actual) 16 GB (Apple)

Type of RAM Slots:
8 - 240-pin PC2-5300 (667MHz) DDR2 ECC fully-buffered DIMM (FB-DIMM) (matched pairs)
 
Any of you guys have an idea what could be wrong with my Mac Pro memory config?

I have a Mid-2010 Quad 2.8 Mac Pro which shipped with the original Samsung 3x1 GB PC3-10600 RAM, that is, well, 1333 MHz.

I ordered two Kingston KTA-1066/4G for a total configuration of 10GB (4-4-1-1).

The problem is, that the machine recognizes all of the memory only in 1-1-4-4 configuration, but only 8 GB in 4-4-1-1 config, which is the recommended one. So it seems to have only 4-4-0-0. I'd appreciate any help, thanks.

EDIT: IT WORKS, no more help needed
 
Last edited:
Just installed one of my spare 2GB sticks in the 4th slot.

Now have 4-4-4-2. Everything is running fine. I'll let you know how it performs over the next few days.
 
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