Some questions about triple channel memory.

[eyeangle]

I want to upgrade the RAM of my Mac Pro 5,1 3.33Ghz. On everymac.com it says this about the memory:

*Four memory slots are provided on the "slide out" processor tray. Note that this model supports triple channel memory addressing and performance is improved by installing memory in groups of three. - Max 48GB

Does that mean that 3 x 4GB is better than 4 x 4GB. And 3 x 8GB better than 4 x 8GB? Why the 4 slots then and not three?

I want to eventually get to 48GB (3 x 16GB) so I think I'll start with 1 x 16GB. Are there any negatives to having 1 Dimm of 16GB when it says it's best to keep them in groups of three?

 

[m4v3r1ck]

Al there is to know about adding RAM...

http://support.apple.com/kb/ht4433

 

[deconstruct60]

Does that mean that 3 x 4GB is better than 4 x 4GB. And 3 x 8GB better than 4 x 8GB? Why the 4 slots then and not three?

There are 4 because what is incrementally "better" depends upon your workload needs.

If your workload consistently needs < 24GB of active RAM, then 3 x8 is better. It is clocked/access faster so you will get higher memory bandwidth. (10% or lower increase depending upon how heavy your app workload is stressing the memory subsystem. )

If your workload consistently needs > 24GB of active RAM ( so that virtual memory paging is relatively active ), then the incrementally slower memory is still orders of magnitude faster than disk IO. Turning off the active memory paging is a bigger benefit if workload's memory footprint stops < 32GB.

Groups of 3 is better for most and is cheaper than "recommending" that folks move up in RAM density in groups of 4. Adding a 4th allows for a trade-off on a bit more capacity with not substantial increase in space utilization. [ Technically each of the 3 can be 'doubled up' to 6 but Mac Pro design doesn't have room for that. ]

I want to eventually get to 48GB (3 x 16GB) so I think I'll start with 1 x 16GB. Are there any negatives to having 1 Dimm of 16GB when it says it's best to keep them in groups of three?

If you don't mind throwing bandwidth down the drain, fine. It isn't a huge amount but won't be getting top multiple core performance out of the machine.

If your apps need less than 16GB and aggressively flush all data it works with to disk it may be a decent trade off. Your apps will be tightly coupled to disk IO throughput anyway so the RAM bandwidth tossing will get "lost" in that overhead.

If workload really does have very high requirements for 48GB, then going to 16GB rather than 24GB is probably not a good idea. With that kind of elevated RAM capacity need, going from 4 x 4GB to 1 x 16GB is going backwards. Not enough capacity and even slower than it was.

If a debate between 4 x 8GB and 2 x 16 then strength a bit on budget and getting 2 x 16GB until can round up money to complete the 3 x 16GB is probably a better move. You also can't mix unbuffered and Registered DIMMs. If don't want to deal with trade-in / swap costs on the transition to 16GB DIMMs then two is better than one.

 

[Raventhornn]

I want to upgrade the RAM of my Mac Pro 5,1 3.33Ghz. On everymac.com it says this about the memory:

*Four memory slots are provided on the "slide out" processor tray. Note that this model supports triple channel memory addressing and performance is improved by installing memory in groups of three. - Max 48GB

Does that mean that 3 x 4GB is better than 4 x 4GB. And 3 x 8GB better than 4 x 8GB? Why the 4 slots then and not three?

I want to eventually get to 48GB (3 x 16GB) so I think I'll start with 1 x 16GB. Are there any negatives to having 1 Dimm of 16GB when it says it's best to keep them in groups of three?

eyeangle, this can be a very slippery slope, because it really starts diving into microprocessor architecture very fast. I will attempt to keep this high level - ok?

Triple channel means that the system writes in an interleaving model [i.e. spread amongst the modules in an alternating pattern], which basically means it writes smaller bits of data to DIMM0, then DIMM1, then DIMM2 - this lowers memory latency - simply put it spreads the load across all three memory modules to make it faster. Populating the 4th DIMM slot introduces additional latency because now there are not just 3 modules for it to spread it's access across evenly.

This is a very simplified expression of what is going on.

From a purely tech specs it will be slower, however will you notice it, probably not, unless you are doing some very computational heavy activities [like 3-d renders].

Hope that helps explain it.

Raventhornn

 

[Studio K]

If you need to use the fourth slot, then you should. The speed penalty will likely not be noticable and will be offset by the presence of the extra ram capacity.

If you can get all of the ram you need in a set of three, then that would be 'optimal'.

The important thing is that you have enough ram available.

 

[eyeangle]

Hi everyone,

Thanks for your help.

I'm confused on the amount of RAM my computer can support. (MacPro5,1 mid2010 3.33GHz) In some of the articles, I've read that it can accept 48GB of RAM, in others articles, that it caps out at 32 GB, in another 16GB.

16GB - Crucial system scanner and http://www.everymac.com/systems/app...ro-six-core-3.33-mid-2010-westmere-specs.html
32GB - http://support.apple.com/kb/SP589
48GB - http://www.everymac.com/systems/app...ro-six-core-3.33-mid-2010-westmere-specs.html

Does anyone know what the maximum is? everymac.com says apple officially support 16GB for this model...

I ended up purchasing 3x8GB from OWC .... may have to return it...

 

[eyeangle]

This is why I'm confused from everymac.com

---> *Apple officially supports 16 GB of RAM in this model. However, as first noted by site sponsor Other World Computing, this model actually can support 48 GB of RAM.
... and on top of that the crucial system scanner also says max 16GB

Okay I understand about the 48GB part, but where on the apple site does it say officially supports 16GB? In their document I found: http://support.apple.com/kb/SP589 it says this model supports 32GB.

 

[DeltaMac]

...
I'm confused on the amount of RAM my computer can support. (MacPro5,1 mid2010 3.33GHz) In some of the articles, I've read that it can accept 48GB of RAM, in others articles, that it caps out at 32 GB, in another 16GB.
...
Does anyone know what the maximum is? everymac.com says apple officially support 16GB for this model...

I ended up purchasing 3x8GB from OWC .... may have to return it...

Yes, the maximum is very confusing - I'll try to simplify (hope I get it right!)
Apple says the max chip in each slot is 8 GB, but others have tested 16 GB chips.
If you have 4 total slots, then Apple max is 32 GB, but with 16 GB chips, you cannot use all 4 slots, so max really is 48 GB.
If you have 8 slots, then 8 GB chips give you 64 GB total, however if you want to use 16 GB chips you are "limited" to 3 in each bank, for a total of 96 GB maximum - unless you are running OS X 10.9 or higher, which can read ALL the slots, and you can fill up with 16 GB chips, for a total of 128 GB

 

[eyeangle]

Thanks for that, I understand that part but why do some sites say that this model has as maximum of 16GB?

 

[eyeangle]

Is this because at the time of posting the results above, 8GB dimms had not been tested yet or there weren't any 8GB dimms of this speed so apple just said the maximum was 4x4GB chips? Or have these sites just simply got it wrong?

 

[DeltaMac]

... why do some sites say that this model has as maximum of 16GB?

AFAIK - Apple did not configure that model with more than 16 GB. The Apple support page for upgrading memory no longer uses that figure, but says 32 GB max - which is also not accurate. The 16 GB figure just doesn't give you all the info that you need, without some more study.

Anyway, I answer your question with another question (which I normally avoid): Does your Mac Pro work with the 24 GB that you ordered?
If it is within the specs required for your Mac Pro, then, yes it will. You will see measurable performance with 3 chips higher than 4 x 8 GB (32 GB) because the memory bus supports try-channel RAM. Real world use - you would unlikely see noticeable difference, which would likely balance out because of the extra memory available.
16 GB cards are a higher density chip, and won't intermix with other sizes, and, on a 4-slot system, can have a maximum of 3 16 GB cards installed - hence, the maximum of 48 GB

When I look at (Crucial.com) the single 3.33 GHz, 6-core processor, mid-2010 MacPro shows a maximum of 32 GB - not 16 GB?

 

[eyeangle]

Thanks DeltaMac that clears things up.

Yes crucial.com does say 32GB for this model but if I use the system scanner from the same site it comes up as 16GB as you can see in the picture above.

The 24GB I ordered should arrive next week.

 

[eyeangle]

I actually received the memory today in the mail and slotted it in. It works perfectly. It was pretty good timing because the ram arrived when an Apple technician was at my house fitting my mac pro with a new logic board. I was having problems with Disk bay 1 not reading hard drives so they sent a techy out here to fix it within a day (gotta love warranty). Anyway as he was fitting the logic board I was installing the ram and he said, "You know, 4 dimms are better than 3 because it works in pairs." I couldn't be bothered going into the whole discussion we've had about about triple channel memory so I just took it as a comment. But it begs the questions, who do you believe in this case?

I went back to everymac.com and looked up my model and this time I couldn't find where it says,
*Four memory slots are provided on the "slide out" processor tray. Note that this model supports triple channel memory addressing and performance is improved by installing memory in groups of three.

Could I have been mistaken? Turns out I was! This comment comes from the 2012 Mac Pros so I'd click the wrong model... unless they've changed it recently.

Anyway, everymac.com says about this model,
3 GB of RAM is installed as three 1 GB modules and 6 GB of RAM is installed as three 2 GB modules. One slot is free.

So maybe after all this model really is triple channel memory as well. I don't know if I will fork out the extra $99.79 for another 8GB dimm, just for my Apple OCD.

EDIT:
I've contacted OWC and they said this:
Your computer is a triple channel computer. I can't begin to discuss what you would go for on this one as I have no information on how you would be using this computer. But there is one rule of thumb to fall back on. More memory trumps memory addressing.