Best memory option for 2010 Mac Pro?

[Neeznoodle]

I am getting ready to upgrade from my 2008 Mac Pro to a refurbished 2010 Mac Pro. It will have 3.2GHz Quad-Core Intel Xeon "Nehalem" (4-Cores; 8-Threads), which is perfect for my needs, but I'm unsure about what memory to use. Here are my choices:

16GB (4x 4GB) of 1333MHz DDR3 ECC
24GB (3x 8GB) of 1333MHz DDR3 ECC
32GB (4x 8GB) of 1333MHz DDR3 ECC

I would be fine with the 16GB, but it's in the back of my mind that some configurations are better than others (I don't know why). So, I would like to know what some of you have to say about this. And, please keep in mind that I'm technically ignorant, meaning if you tell me something like "three dimms are best", I won't have a clue what you mean.

 

[h9826790]

IMO, 3x8 should be a better option (if 16G is good enough for you). And if you need more later on, you may just get an extra stick to make it 4x8.

 

[IowaLynn]

I am getting ready to upgrade from my 2008 Mac Pro to a refurbished 2010 Mac Pro. It will have 3.2GHz Quad-Core Intel Xeon "Nehalem" (4-Cores; 8-Threads), which is perfect for my needs, but I'm unsure about what memory to use. Here are my choices:

16GB (4x 4GB) of 1333MHz DDR3 ECC
24GB (3x 8GB) of 1333MHz DDR3 ECC
32GB (4x 8GB) of 1333MHz DDR3 ECC

I would be fine with the 16GB, but it's in the back of my mind that some configurations are better than others (I don't know why). So, I would like to know what some of you have to say about this. And, please keep in mind that I'm technically ignorant, meaning if you tell me something like "three dimms are best", I won't have a clue what you mean.

24GB use to be "sweet spot" and likely still is, and even if 16 seems and sounds like 'enough' giving some for caching volumes, system, apps and of course data - and in-memory cache (virtual memory scratch).

Hopefully a nice shiny new SSD device is in your future

 

[Neeznoodle]

Thank you, both of you, for your input. And, yes, my 2010 will include an SSD. It should be a great computer that will last me many years, just as my 2008 did.

 

[Inutopia]

Just get as much as you need. Fill all the slots if you want, the difference wont be much. If it helps I run with 8x4Gb and everything works very well.

 

[flowrider]

As stated above, 24GB. But, no one has stated the reason. The CPU utilizes three memory channels and for optimum performance slots 1 thru 3 should be filled with equal sized and speed (best if it's identical) RAM. Slots 3 and 4 are electrically tied together and populating slot 4 slows things down a bit. Not much, and something you may not even notice, but there is a slight performance hit. Best to leave slot 4 MT. My memory supplier since 1986 has been:

http://www.datamemorysystems.com/ap...-2ghz-mc560ll/a-cto-mid-2010-memory-upgrades/

BTW, the 2010 3.2MHz Mac Pro utilizes the W3565 CPU and the Max RAM speed of that chip is 1066MHz. 1333MHz RAM will certainly work, but will not run at full speed with the stock CPU.

http://cpuboss.com/cpu/Intel-Xeon-W3565

https://support.apple.com/kb/SP589?locale=en_US

Lou

 

[Demigod Mac]

3x16GB (48GB) is also an option.

http://www.datamemorysystems.com/dm61-765/

 

[Neeznoodle]

As stated above, 24GB. But, no one has stated the reason. The CPU utilizes three memory channels and for optimum performance slots 1 thru 3 should be filled with equal sized and speed (best if it's identical) RAM. Slots 3 and 4 are electrically tied together and populating slot 4 slows things down a bit. Not much, and something you may not even notice, but there is a slight performance hit. Best to leave slot 4 MT.

Thank you so much for explaining this! I placed my order last night and it will have 24GB. I'm starting to feel like a kid on Christmas Eve!

 

[warrenl]

Although it will run on 1066MHz, for more or less the same price you should get 1333MHz, as it future proofs you investment if you want to do an upgrade to a six core CPU

 

[Arron Rouse]

As stated above, 24GB. But, no one has stated the reason. The CPU utilizes three memory channels and for optimum performance slots 1 thru 3 should be filled with equal sized and speed (best if it's identical) RAM. Slots 3 and 4 are electrically tied together and populating slot 4 slows things down a bit. Not much, and something you may not even notice, but there is a slight performance hit.

I'd know about this since the release of Nehalem. Now revelation has finally hit. If you're using three slots, 100% of your RAM is running at 100% bandwidth. If you're using 4 slots, 50% of your RAM is running at 50% bandwidth. That means you're only going to get 75% bandwidth if you're using a lot of RAM. Which explains the benchmarks being a bit scattered performance-wise.

The upshot is counter-intuitive: if you use a lot of memory, you're better off using 3 slots. Sometimes it takes me a while to put two and two together.

 

[h9826790]

if you use a lot of memory, you're better off using 3 slots.

I think it should be the other way around. If we use a lot of RAM, we should install as much RAM as possible, because if we run out of RAM, there will be a huge performance hit. On the other hand, if we only use little memory, then only use 3 slots to fully utilise the triple channel configuration will make your machine run a bit faster (but not noticeable in most real world application).

I believe that your conclusion is based on a wrong assumption - There is no performance hit if we run out of RAM.

 

[Arron Rouse]

I think it should be the other way around. If we use a lot of RAM, we should install as much RAM as possible, because if we run out of RAM, there will be a huge performance hit. [...] There is no performance if we run out of RAM.

I got some time and went hunting. Flowrider was a little off the mark. The RAM doesn't share a channel, it interleaves. It works like this:

• All of the RAM slots run at the same speed whether you've got a single or dual processor machine
  
• 1033MHz RAM sticks will give you 8.5GB/s each and 1333MHz RAM sticks will give you about 11GB/s each
• However, the first 3 slots for each processor are interleaved

So the bandwidth you get with, for example, 1333MHz 8GB RAM sticks:

• Slot 1 only populated -- 8GB at 11GB/s
• Slots 1 & 2 populated -- 16GB at 22GB/s
• Slots 1, 2 & 3 populated -- 24GB at 33GB/s
• Slots 1, 2, 3 & 4 populated -- 24GB at 33GB/s and 8GB at 11GB/s

So it turns out that it may depend on what software you're using as to whether it makes sense to populate Slot 4. For applications that use a lot of static data such as big images in PhotoShop, using Slot 4 is a good idea. As h9826790 says, running out of RAM would be bad.

Conversely, I use a lot of VMs which need reliable memory bandwidth or their performance can be crushed. In that case, it's possible that Slot 4 should be empty. But only possible. After all, 24GB at 33GB/s and 8GB at 11GB/s is still better than 24GB at 33GB/s by itself. However, my experience (without any kind of formal testing) seems to point to lower performance with VMs if Slot 4 is populated.

One of the things that worries me about using Slot 4 is that the CPU fills the fast RAM first. Which in theory means that static data you've loaded, e.g. large textures that only get read once in a render, could be sat in the fast zone pushing all the stuff that needs performance into the slow zone.

Then there's the fact that, as h9826790 implies, slow RAM is probably still better than being pushed out to a swap file.

All in all, I suspect that the best performance will be something that depends on the type of workload.

 

[flowrider]

^^^^Where did you go hunting? Slots 3 & 4 are electrically connected, with slot 3 having the third channel path to the CPU. If you don't populate slot 3, and do populate slot 4, the RAM installed in slot 4 will not show. Slots 3&4 (7&8) are in fact shared and electrically connected.

http://apple.stackexchange.com/ques...-slots-in-dual-channel-mode-or-6-ram-slots-in

As far as interleaved RAM goes, if memory serves me correctly, Interleaved RAM was used on the 2007 and 2008 (1,1 - 2,1 and 3,1) Mac Pro. The 4,1 and 5,1 uses CPUs with three discreet RAM channels electronically connected to the slots on the MoBo.

Lou

 

[Arron Rouse]

^^^^Anandtech was the main source but I did look at quite a few sites.

http://www.anandtech.com/show/2658/5

The main quote was:
In the four-slot configuration the first three slots correspond to the first three channels, the fourth slot is simply sharing one of the memory channels. The downside to this approach is that your memory bandwidth drops to single-channel performance as you start filling up your memory. For example, if you have 4 x 1GB sticks, the first 3GB of memory will be interleaved between the three memory channels and you'll get 25.6GB/s of bandwidth to data stored in the first 3GB. The final 1GB however won't be interleaved and you'll only get 8.5GB/s of bandwidth to it.

 

[flowrider]

^^^^That was written back in 2008 and not Mac related. The configurations in that article are different than what we have in a Mac Pro and they do state what they were writing was theoretical. I'm not smart enough to know if it's Mac applicable or not.

Lou

 

[Arron Rouse]

^^^^ The article is about Nehalem which was the architecture used in the 2009 Mac Pro. The 2010 Mac Pro uses Westmere -- a die-shrink of Nehalem. The PC and Mac motherboard layouts are different but that's only the layout. So the article isn't exactly on the money but is applicable.

I do owe you an apology, though. That fourth slot does share a channel exactly as you said.

Thinking it through, that means my last bullet was a little misleading.

• Slots 1, 2, 3 & 4 populated -- 24GB at 33GB/s and 8GB at 11GB/s

The thing is, for each memory read/write, you only get one or the other.

 

[ActionableMango]

As far as interleaved RAM goes, if memory serves me correctly, Interleaved RAM was used on the 2007 and 2008 (1,1 - 2,1 and 3,1) Mac Pro. The 4,1 and 5,1 uses CPUs with three discreet RAM channels electronically connected to the slots on the MoBo.

The LGA1366/IntelX58 platform can operate in interleaved mode across two or three controllers. I assume there is nothing special about the Mac Pro 2009-2012 that prevents this from happening.