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Mac Pro 3,1 RAM configuration

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Walddo

macrumors newbie
Original poster
Feb 4, 2008
8
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I need some advice on RAM configuration for a Mac Pro 3,1. Does anyone knows if there is any disadvantage in mixing 8GB (4GBx2) of memory with 4GB (1GBx4) for a total of 12GB? The 4GB sticks would be placed on different risers and the remaining 1GB sticks two on each, giving 6GB per riser. Is that advisable?

Thanks in advance.
 
You can't place the 4GB DIMMs on seperate risers. Put them on Riser A and the four 1GB DIMMs on Riser B.
 
I have the MacPro3,1 which is the Early 2008 with FB-DIMMs. They must be installed in matching pairs:

MacPro_Early2008_MemoryDIMM_DIY.pdf

According to Apple, you'll put your two 4GB and two 1GB on riser A and two 1GB on riser B. I would assume Apple knows best unless there's some other reason I don't know about to do it differently.

Walddo said:
I need some advice on RAM configuration for a Mac Pro 3,1. Does anyone knows if there is any disadvantage in mixing 8GB (4GBx2) of memory with 4GB (1GBx4) for a total of 12GB? The 4GB sticks would be placed on different risers and the remaining 1GB sticks two on each, giving 6GB per riser. Is that advisable?

Thanks in advance.
Click to expand...
 
sadd3j said:
I have the MacPro3,1 which is the Early 2008 with FB-DIMMs. They must be installed in matching pairs:

MacPro_Early2008_MemoryDIMM_DIY.pdf

According to Apple, you'll put your two 4GB and two 1GB on riser A and two 1GB on riser B. I would assume Apple knows best unless there's some other reason I don't know about to do it differently.
Click to expand...

Ideally you should have the same amount of memory on each riser, if not able to do so then next you should have as little difference as possible between them.
 
Umbongo said:
Ideally you should have the same amount of memory on each riser, if not able to do so then next you should have as little difference as possible between them.
Click to expand...

How come? I've never read or tried anything to support that, I'd be curious to know the reason. The main thing I think is just to keep the matched pairs in a single riser.

According to OWC, you get the biggest performance differences due to RAM configuration if you have a 2.8 octo, as opposed to just a quad. Basically fill as many slots as you can.

OWC article about different RAM configurations in Early 2008 Mac Pro

MEMORY TESTS, TAKE 2:
"early 2008" Mac Pro 3.2GHz 8-core
 
sadd3j said:
How come? I've never read or tried anything to support that, I'd be curious to know the reason. The main thing I think is just to keep the matched pairs in a single riser.

According to OWC, you get the biggest performance differences due to RAM configuration if you have a 2.8 octo, as opposed to just a quad. Basically fill as many slots as you can.

OWC article about different RAM configurations in Early 2008 Mac Pro

MEMORY TESTS, TAKE 2:
"early 2008" Mac Pro 3.2GHz 8-core
Click to expand...

If you are accessing 10GB from one riser and 2GB from another that is not balanced. It is all about balance to recieve the greatest performance. Although Apple do not talk about it it is covered in FB-DIMM related articles and documentation.

Although this chart doesn't cover 4GB DIMMs the princibles of 2GB and 512MB DIMMS found in 6C should be applied to this situation.
 
Thanks for all your responses.

Would I be better of purchasing 8GB of RAM in 2GB sticks thus filling all slots? I asked for the first option because next year I will probably replace all 1GB and the 4GB sticks would give me the path to 32GB when due time, but if the performance impact of this approach in the mean time is noticeable I wouldn't mind going for the 2GB: 16GB total is enough for me for a while.
 
Walddo said:
Thanks for all your responses.

Would I be better of purchasing 8GB of RAM in 2GB sticks thus filling all slots? I asked for the first option because next year I will probably replace all 1GB and the 4GB sticks would give me the path to 32GB when due time, but if the performance impact of this approach in the mean time is noticeable I wouldn't mind going for the 2GB: 16GB total is enough for me for a while.
Click to expand...

I'd go for the 2GB DIMMs. 2x2GB (slot 1&2) and 2x1GB on each riser :)
 
hay i have a macpro 3.1 8-core, 10 gb of ram (2x1gb & 4x2GB), works fine as long as your using matched pairs.
while an un-optimised ram placement will not give ideal speed's it will be faster than running out of ram.
(the OWC chart shows it's less important on a 4 core)

id grab the 2GB sticks as they where cheeper for me (8Gb of ram in 2GB sticks was cheeper) so i assume cheeper for you then if you need at a later date you can replace the 1GB sticks (wont matter if you replace with 2GB or 4GB sticks at that point).

id relay not even think about hitting 34GB of ram on a macpro 3.1 it'll cost less to buy a macpro 4/5 and the ram and be much faster, if you actually do need 32 GB of ram you will also need the faster computer.
this is fun to http://macperformanceguide.com/Mac-Monitoring-memory.html

edit-
it will work with 4x1Gb & 2x4gb of ram, it just will not be at optimal speed but it will be faster than having to little ram. if the 4Gb sticks are cheeper than the 2GB sticks id think about it but the 2GB sticks will be faster.

this shows that un-optimal ram placement make's vary little speed difference in photoshop Cs5 http://macperformanceguide.com/Reviews-MacProWestmere-MemoryBandwidth.html (on a macpro 2010 but i dont think it will change a lot)
 
Last edited:
emjayen84 said:
So, I could install two new 4GB units on separate risers, with two extra 2GB units that I already have, on each riser and it would work?
Click to expand...

Not sure I follow.

If you mean the layout below, then yes.

Riser 1: 4GB, 4GB, 2GB, 2GB
Riser 2: 4GB, 4GB, 2GB, 2GB
 
Your original choice of RAM config is fine, as OWC report in previous posts the only further optimisation would be all slots filled with identical modules.
8 x 1GB or 8 x 2GB would be the fastest and probably the most cost effective formation. I went 8 x 2GB when Memory America had an offer on.
 
Umbongo said:
Not sure I follow.

If you mean the layout below, then yes.

Riser 1: 4GB, 4GB, 2GB, 2GB
Riser 2: 4GB, 4GB, 2GB, 2GB
Click to expand...

edit: Actually, I only have TWO 4GB cards, and TWO 2GB cards, so this won't work?:

Riser 1: 4GB, 2GB
Riser 2: 4GB, 2GB

How would you recommend doing it with what I have?
 
emjayen84 said:
edit: Actually, I only have TWO 4GB cards, and TWO 2GB cards, so this won't work?:

Riser 1: 4GB, 2GB
Riser 2: 4GB, 2GB

How would you recommend doing it with what I have?
Click to expand...

Riser 1: 4GB, 4GB
Riser 2: 2GB, 2GB

That's fine. You have to match pairs if you have more than 2 DIMMs (cards). Although you don't have the same memory capacity on each riser that's low down the list of things that cause performance issues. Many people ran that configuration, or 2GB, 2GB / 1GB 1GB when they upgraded.
 
1 GB being read as 512 MB

In my Mac Pro 3,1, I have 10 GB of Ram installed as follows:
Riser A: 2 x 1GB (in 3/4) / 2 x 2 GB (in 1/2)
Riser B: 4 x 1 GB

On most restarts, the system profiler reads the 1GB sticks on Riser B (1/2) as 512MB for total of 9 GB RAM, and other times as 1 GB, for a total of 10 GB RAM.

Is there a better configuration so they are always read as 1GB?
 
joedds said:
In my Mac Pro 3,1, I have 10 GB of Ram installed as follows:
Riser A: 2 x 1GB (in 3/4) / 2 x 2 GB (in 1/2)
Riser B: 4 x 1 GB

On most restarts, the system profiler reads the 1GB sticks on Riser B (1/2) as 512MB for total of 9 GB RAM, and other times as 1 GB, for a total of 10 GB RAM.

Is there a better configuration so they are always read as 1GB?
Click to expand...

I would be sure to try reseating all the RAM sticks.
Swap the pair in B, 1/2 with A, 3/4
If the read problem follows the sticks, then those sticks should be replaced.
If the read problem stays with the same position (B, 1/2) then try swapping the risers (they are interchangeable), and watch if the same problem continues with the same riser card (now in the upper position)
Double-check that each pair of your RAM sticks have identical specs from the same manufacturer. Each pair should be matched in type and vendor (manufacturer). Different pairs can vary, as long as each pair is matched.
 
What the..?

Do any of you experts know why my MacPro3,1 (early 2008) isn't reading 4 out of the 8GB I installed in it today? The tower came with 2GB, I added 2x1GB sticks a couple years ago, and today, installed 4X2GB sticks, and it now only reads 8GB? I also see one solid red light (DIMM 3) on one of my RAM cards - Could this be caused by the difference in memory capacity Umbongo was talking about? Here's a picture of my profiler: http://imgur.com/4be7EqZ
(attachments aren't working, so I posted a link)

Thanks,
Matt
 
Last edited:
emjayen84 said:
Do any of you experts know why my MacPro3,1 (early 2008) isn't reading 4 out of the 8GB I installed in it today? The tower came with 2GB, I added 2x1GB sticks a couple years ago, and today, installed 4X2GB sticks, and it now only reads 8GB? I also see one solid red light (DIMM 3) on one of my RAM cards - ...
Click to expand...

The red light next to a memory slot means that there is a problem with the RAM card in that slot.
Your system profiler shows that no RAM is reading in the upper riser, slots 3 and 4. If the light is near slot 3, in the upper riser, then likely it's one memory stick that is not seated properly.
Try swapping the pair of 2GB cards between the upper (A) and lower (B) risers.
Be particularly careful (and firm) with seating. It's quite easy to have memory cards that are not seated properly in the slots. In addition, if one of a pair is not seated, then neither will work.
If swapping the pairs doesn't help (and the bad pair swaps to riser (B) ), then you likely have a bad stick. New memory usually will have warranty.
Hopefully, the seating will get all your memory working.
 
DeltaMac said:
The red light next to a memory slot means that there is a problem with the RAM card in that slot.
Your system profiler shows that no RAM is reading in the upper riser, slots 3 and 4. If the light is near slot 3, in the upper riser, then likely it's one memory stick that is not seated properly.
Try swapping the pair of 2GB cards between the upper (A) and lower (B) risers.
Be particularly careful (and firm) with seating. It's quite easy to have memory cards that are not seated properly in the slots. In addition, if one of a pair is not seated, then neither will work.
If swapping the pairs doesn't help (and the bad pair swaps to riser (B) ), then you likely have a bad stick. New memory usually will have warranty.
Hopefully, the seating will get all your memory working.
Click to expand...


Thanks for the reply. I swapped RAM cards places on riser A (DIMM3 & 4 slots) and now it's only DIMM 4 that has a solid red light, so it seems atleast that one stick is bad? If both were bad, would both of their respective lights be on? Is it the same as if one card were seated wrong, making both slots register as nothing? (only 8GB instead of 12GB?) Either way, the 2X2GB sticks came as a package.
 
It is likely a bad FB-DIMM, but you could try cleaning the contacts with isopropyl alcohol. Use a cotton swab dipped in 91% isopropyl alcohol solution to clean the gold plated contacts.

If this does not correct the issue the module has failed. Some memory has lifetime warranty and you can RMA it with the seller. I have had two pairs of memory replaced on my Mac Pro via OWC's warranty free of charge.
 
cosmos said:
It is likely a bad FB-DIMM, but you could try cleaning the contacts with isopropyl alcohol. Use a cotton swab dipped in 91% isopropyl alcohol solution to clean the gold plated contacts.

If this does not correct the issue the module has failed. Some memory has lifetime warranty and you can RMA it with the seller. I have had two pairs of memory replaced on my Mac Pro via OWC's warranty free of charge.
Click to expand...

Thanks
 
Last edited:
emjayen84 said:
My question is though, is it just one of the cards that is bad, since only one makes whichever slot it is in's, light turn red? And if it is only one that is bad, is that why my computer only says 8GB, instead of 12GB, because it makes the pair of slots (DIMM 3 & 4) read as no RAM (both 2GB sticks) being installed in them?
Click to expand...

The RAM must be installed in banks. If you have a failure of one module, it will remove both modules from the mix. If the memory is under a lifetime warranty, most vendors will replace both modules. At least OWC replaces them in pairs.
 
cosmos said:
The RAM must be installed in banks. If you have a failure of one module, it will remove both modules from the mix. If the memory is under a lifetime warranty, most vendors will replace both modules. At least OWC replaces them in pairs.
Click to expand...

So does Transcend! :cool:
 
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