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Memory configuration Question...

B

Brianone20

macrumors newbie
Original poster
Jan 13, 2011
7
0
Hello, I am a brand new member on this forum. I have been utilizing it for years and I usually find my answer very quickly. However, I have searched and found discussion regarding my issue, but nothing directly spoke to the question I have.

If there is a simple link someone can provide to a similar discussion I would be grateful.

My question is about RAM in the mac pro. I have a 8 core, 3.0 machine that has 8GB of RAM installed. The configuration is set up as 1GB modules in 8 slots.

Can I buy/install 4, 4GB modules and remove 4, 1GB modules? If so, what would the correct configuration be? From what I've read, keeping the same size together is the way to go?

So, 4,4,4,4 and 1,1,1,1 ? Or should they be staggered like 4,4,1,1 and 4,4,1,1 for a total of 20GB?

OR is this entirely a bad idea? Should I start over and go 2,2,2,2 and 2,2,2,2
for a total of 16GB.

Just not sure about the logistics of what these boards like and if there are bottle necks I'm at risk of here.

Any help is greatly appreciated and I know many others would benefit from a discussion on this matter.
 
Hi Brianone20,

As long as you keep matched pairs together, any configuration will work, but the generally recommended configuration for what you're talking about would be 4,4,1,1 in each drawer. And yes, if there is any chance you want to add more in the future, go with the 4GB sticks rather than the 2GB.

That said, I have seen charts of performance that show that having all of one type of memory in all 8 slots gives a *small* performance boost - so 8GB, 16GB, and 32GB are generally considered the sweet spots, but that is going to be a very small thing compared to the jump from 8GB to 20GB.

Here's a more detailed report from barefeats:

http://www.barefeats.com/harper3.html
 
Last edited:
Besides if you do it wrong, you'll get a notification once you've booted up telling you it's wrong.
 
Actually, if you look at those charts from Barefeats, and also from OWC, there are several ways that you can install memory that the computer will boot up, but performance will take a big hit. The big ones all involve leaving one tray empty while loading up another, but smaller hits come in many forms. I'm not sure, but I think the only configuration that will actually keep the machine from booting up is not installing matched pairs.
 
Stephen23 said:
Actually, if you look at those charts from Barefeats, and also from OWC, there are several ways that you can install memory that the computer will boot up, but performance will take a big hit. The big ones all involve leaving one tray empty while loading up another, but smaller hits come in many forms. I'm not sure, but I think the only configuration that will actually keep the machine from booting up is not installing matched pairs.
Click to expand...

Huh? With FBDIMMs you will get less latency (=faster) by putting DIMMs in slots 1 and 2 on each riser.

For example,
2 2
2 2

will be faster than

2 2 2 2

or

1 1 1 1
1 1 1 1

@OP

4 4 1 1
4 4 1 1

Is the correct configuration if you need 20 gigs of RAM. If you are not getting page outs (check the activity monitor at the end of the day), I would remove the 1gb sticks and see if it's faster.

If you do indeed require 20gbs, 4 gigs of extra RAM negates the speed "bonus" you would get from using matched RAM / not using slots 3 and 4.
 
gullysnowcat,

the post you responded to was regarding configurations that would not allow the machine to boot up, or would cause a performance hit - hence your confusion. If you'd looked at the entire thread, you would have seen that the OP's original question was already answered properly above.
 
Stephen23 said:
gullysnowcat,

the post you responded to was regarding configurations that would not allow the machine to boot up, or would cause a performance hit - hence your confusion. If you'd looked at the entire thread, you would have seen that the OP's original question was already answered properly above.
Click to expand...

Yep sorry for the misunderstanding. *Hug*:D
 
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alphaod said:
Besides if you do it wrong, you'll get a notification once you've booted up telling you it's wrong.
Click to expand...

If you get it right you also get a message telling you everything is fine ! ^^
 
Try varying the layout.

I noticed on geekbench scores for Mac Pro the most obvious configs don't give the fastest memory use scores, I would experiment with the layout and Geekbench each config to see which it likes best.

Set 1: 4,4 1,1 (1st Riser) 4,4 1,1 (2nd Riser)

Set 2: 1,1 4,4 (1st Riser) 1,1 4,4 (2nd Riser)

Set 3: 4,4 4,4 (1st Riser) 1,1 1,1 (2nd Riser)

Set 4: 1,1,1,1 (1st Riser) 4,4 4,4 (2nd Riser)

If you could post the test results here too I would be very grateful.
Note: You will have to have a full fat 64-bit version of Geekbench to get accurate figures and switching the OS to 64-bit native boot may affect the results too.
 
OK, I will mess with this and post results. But, it may be a while because I need this machine full time right now... Sorry, I appreciate all the help and I will get to this as soon as possible.

For now I am going to go with 4411 and 4411.
 
I've got a similar issue. My original configuration is Riser 1 - 2, 2, X, X. Riser 2 - 2, 2, X, X. I wanted to increase the ram so I ordered two sticks of 4 each. Per everything I could find I added them to Riser 1 as a pair so my configuration is now Riser 1 - 2,2,4,4, and Riser 2 is 2,2,X,X. The memory works (no error message) but its only recognizing a total of 12 ram. 2 for each. Any thoughts?
 
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