Octad 2008 Memory Placement on Risers

[waitingallday]

After reading Apple dox and lots of postings, I am still confused on how to get the appropriate amount of memory and combine it with riser placement for best bandwidth. I would to buy 4G modules and end up with at least 10 Gb instead of the current stock 2 Gb.

So…I ordered 8Gb and am now confused…

Ideally, can I simply move both 1Gb x 2 to the lower riser and install the 4Gb x 2 in the upper riser and have the best bandwidth? Should I purchase/match 8Gb more and put those in the lower riser and toss the stock 2Gb? Am I not going to notice any of this anyways and just be happy I'm feeding my 2 Virtual Machines more memory?

 

[dcpmark]

Just did the same thing: after reading the User Guide, I moved the 1GB DIMM to the top card, and put the 4GB DIMMs in slots 1&2 of the bottom card. The result was 10GBs in matched pairs.

 

[waitingallday]

I though it would work, but I guess my question was more specific towards the number of memory modules, their “rank”, and their proper installation since all of these will affect the memory bandwidth (speed) on the 2008 Mac Pro. In the end, it's clear that not having the right 'mix' will slow down bandwidth throughput. See here and here for speed tests.

I've read the notion that you should ideally have the same amount of memory on each riser and, if not able to do so, then next you should have as little difference as possible between them.

Does anyone else know the 'right' way to deal with so there is minimal (or no) slowdown in bandwidth:

• Choice 1: (2 x 4Gb) + (2 x 1Gb) = 10Gb total & keep stock memory
• Choice 2: (2 x 4Gb) = 8Gb total & toss stock memory
• Choice 3: (2 x 4Gb) + (2 x 4Gb) = 16Gb total & keep stock memory & buy matching for each riser

I know that choice 3 is ideal, but it costs the most. Any thoughts about Choice 1 or 2?

P.S. I wish this chart would show 4Gb modules, but it doesn't.

 

[bigbird]

The RAM chart you link to is the wrong chart for the 2008 MP. You have linked to the 2007 MP memory chart. Why? Because it shows 512K memory modules. The 512 MB modules only came with the 2007 MP.
For your 10GB of RAM (4 X 2) + (2 X 1), put the 2GB modules in risers A & B, slots 1 & 2. Then put a 1GB module in risers A & B, slot 3. Leave slot 4 of both risers empty.

 

[gugucom]

The memory chart is applicable because it is still a dual channel system. You only have to translate the principle to different module sizes.

Option 1 is better than 2 because it creates the bigger capacity without violating the rules. I would not follow big birds proposal. He also seems to have read your capacities wrong and assumes you have 4 x 2GB modules.

 

[waitingallday]

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Much thanks!

 

[dcpmark]

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Much thanks!

Thank YOU for being up this topic.....I had no idea that I might be running an inefficient memory setup. I'm actually going to exchange the memory I just got from OWC and get a better configuration (either 8 x 1GB sticks or 8 x 2Gb sticks).

In the meantime, I guess I should switch mine to 1GB+4GB on each card, right?

UPDATE: I guess not. That configuration reports as only 8MB, and the Mac Pro is reporting that the slots occupied by the 1GB DIMMSs are empty.

 

[Maxian]

I have on a 8x2.8 late 2008 Mac Pro the following memory setup:

Riser A: 4x2 Gb

Riser B: Dimm 1&2 - 1x2 Gb
Dimm 3&4 - 2x2 Gb

for a total of 14Gb.

Do you guys think its ok or would it be better to toss out the 1Gb modules and make them all 2Gb size ?

 

[gugucom]

I have on a 8x2.8 late 2008 Mac Pro the following memory setup:

Riser A: 4x2 Gb

Riser B: Dimm 1&2 - 1x2 Gb
Dimm 3&4 - 2x2 Gb

for a total of 14Gb.

Do you guys think its ok or would it be better to toss out the 1Gb modules and make them all 2Gb size ?

I would swap the 1 GB and 2 GB DIMMs on riser B. The lower slots should have the higher capacity. No point to waist the 1 GB DIMMs and reduce your capacity. But if you have the funds to make them all 2 GB it would probably make the machine a little faster and add capacity.

 

[rtrt]

1

 

[Umbongo]

have to admit to being confused in trying to apply the 'rules' to my situation

have the original 2 x 1G, expanded to 10G with 4 x 2G a while back and an additional 2 x 4G soon = 18G. its a mp2008

the owc/bf links say that it's best to have matching pairs btwn risers a and b - suggesting i split the 2Gs across the risers.

In the pic linked above - if i look at the 9G example - am assuming it applies, as dividing all of my modules by 2 gives 9G. So 1G = 512M, 2G = 1G and 4G = 2G. Pic then shows all of the 2G (1G actually in pic) on the same riser.

Also in that pic i'm not sure which is slots 1 & 2 and which are 3 & 4 - seems reasonable to assume count from top down ie top = 1 and bottom = 4?

Appreciate pic is for the mp2007 but understand from gugucoms comment that it still applies.

anyone care to comment and tell me the best route to go and why

9A is applicable for you. They are arranged like that so that the largest capacity DIMMs are in the first (lowest latency) slots and that each riser has a similar amount of memory for balance. The performance differences between many optimal and non-optimal arrangements are unlikely to have any real impact on most creative professionals, but no harm in having them arranged correctly.

 

[gugucom]

Unless my memory fails me the slots in the risers are counting from 1 to four with the lowest being named 1.

The rules say you need to install DIMMs in pairs on the risers which means slot 1 and 2 and also slot 3 and 4 should have the same DIMMs.

The biggest DIMMs should go into the lowest slots.

Risers should be filled symmetrically if possible. So if you have four of the biggest DIMMs you should fill A1, A2, B1, B2 with them.

If you still have two more of the same capacity you first fill A3 and A4 and fill B3 and B4 poetntially with smaller DIMMs if you have them.

 

[rtrt]

1

 

[gugucom]

I guess Umbong's fit would be better because the Risers would have a better balance of capacity. But one can derive those things by looking at the linked pic.

 

[rtrt]

1