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Best amount of RAM in a Nehalem Mac Pro?

J

jjahshik32

macrumors 603
Original poster
Sep 4, 2006
5,366
52
I'm torn between 12GB vs. 16GB. If I buy the 8x2GB its so much cheaper but does this mean that triple channel wont be used?

I've read somewhere on these threads (an older thread from googling) that the if the first 3 RAM slots match (in this case 2GB dimms) then it should enable tripple channel + the rest 2 should be used as single. Is this true?

If so then I should just get the 8x2GB configuration.
 
I presume you're talking about the 8-core MP with 8 slots, in which case the best configuration (channel-wise) is to go with 6 memory modules. It gives you the triple channel mode.

Then again, if you really do need the additional 4 GB of RAM, then go with 8x2.
 
jjahshik32 said:
I'm torn between 12GB vs. 16GB. If I buy the 8x2GB its so much cheaper but does this mean that triple channel wont be used?

I've read somewhere on these threads (an older thread from googling) that the if the first 3 RAM slots match (in this case 2GB dimms) then it should enable tripple channel + the rest 2 should be used as single. Is this true?

If so then I should just get the 8x2GB configuration.
Click to expand...

fill it up. you wont know the diff between 16 and 12.
 
I feel 12GB is plenty and I'm the one always complaining about not-enough RAM.

I'd just get the 12GB and later down the line if you need it, you can always at the 2 additional modules.

I don't really know what you mean when you say 8x2GB is cheaper; if it is, then buy that and still just install 6x2GB to see if it suits your needs and if not, install the additional sticks.
 
I just decided on 4x4gb for now for a total of 16GB and in the future I'll add another 4x4gb for a total of 32GB. :D
 
The best amount of RAM for a 2009 Mac Pro is the greater of:
- A multiple of 3 DIMMS (Quad) or 6 DIMMS (Octo)
- What you need to avoid page-outs

It's more important to have enough memory than top performing memory, but it's ideal to have both.
 
I would actually buy it with as little RAM as possible, then upgrade the RAM yourself, this will save a substantial amount of money, as Apple way overcharges for the RAM
 
matthewtoney said:
I just order 12GB (3 X 4GB) from Newegg for mine, but I have the quad-core so I had no choice about it really for going over 8GB. I got it for $339 which seems pretty good to me for the 4GB sticks - I'll post here when it arrives how it works if anyone wants.

http://www.newegg.com/Product/Product.aspx?Item=N82E16820220408
Click to expand...

That's a smokin deal... let me know how it works out... I will likely do the same! :D

EDIT: It doesn't mention a thermal sensor, which I thought is a requirement for the Mac Pro?
 
I always buy my Mac Pro's RAM from transintl.com I think their RAM is of high quality.

Anyway, anyone know if I mix in the 1GB DIMMS in with the 4GB? I think I've read that you cant because after I put in the 4x4GB I'd like to fill in the rest with 1GB.
 
VirtualRain said:
The best amount of RAM for a 2009 Mac Pro is the greater of:
- A multiple of 3 DIMMS (Quad) or 6 DIMMS (Octo)
- What you need to avoid page-outs

It's more important to have enough memory than top performing memory, but it's ideal to have both.
Click to expand...

Page outs is kinda a funny thing I still get them with 32GB of RAM. 32-bit software is more of a problem than a lack of RAM for me. The 64-bit era can't come soon enough.
 
VirtualRain said:
That's a smokin deal... let me know how it works out... I will likely do the same! :D

EDIT: It doesn't mention a thermal sensor, which I thought is a requirement for the Mac Pro?
Click to expand...

My understanding (which could be mistaken) is that at least as of a couple of years ago, using DIMMs without a thermal sensor would work fine, but would cause the Mac Pro to run the fans (not sure which or if all) at full speed all the time. I have no idea whether or not that is still the case, or whether or not those DIMMs I order have a thermal sensor or not (although as you mentioned they don't say anything about it) but I guess I'll find out! :)
 
matthewtoney said:
My understanding (which could be mistaken) is that at least as of a couple of years ago, using DIMMs without a thermal sensor would work fine, but would cause the Mac Pro to run the fans (not sure which or if all) at full speed all the time. I have no idea whether or not that is still the case, or whether or not those DIMMs I order have a thermal sensor or not (although as you mentioned they don't say anything about it) but I guess I'll find out! :)
Click to expand...

Do keep us updated. If they work well (without constant full speed fan), I would purchase the same ones for my quad.
 
New RAM

XandeR803 said:
Do keep us updated. If they work well (without constant full speed fan), I would purchase the same ones for my quad.
Click to expand...

Well I've got them now and they're in my 2009 Mac Pro Quad - they work great and the fan speeds haven't changed at all - don't know whether or not that's because these things really do have a thermal sensor, or just that with the 2009 Mac Pro models perhaps the full-speed-fan stuff doesn't happen anymore. Regardless, I can easily recommend that $339 deal now from Newegg for 3 matched-pair 4GB sticks.
 
jjahshik32 said:
I just decided on 4x4gb for now for a total of 16GB and in the future I'll add another 4x4gb for a total of 32GB. :D
Click to expand...

I'm interested to know how you have your memory arranged.

The best choice is probably having two 4GB DIMMs for each processor as you'd get more perfromance stability that way. About 75% of the performance youd see if both had 3 DIMMs.
 
matthewtoney said:
Well I've got them now and they're in my 2009 Mac Pro Quad - they work great and the fan speeds haven't changed at all - don't know whether or not that's because these things really do have a thermal sensor, or just that with the 2009 Mac Pro models perhaps the full-speed-fan stuff doesn't happen anymore. Regardless, I can easily recommend that $339 deal now from Newegg for 3 matched-pair 4GB sticks.
Click to expand...

Sweet... that's great! :D

dekka007 said:
Newegg out of stock of that set can i use the following memory in my 2009 Quad, Although it will still only run at 1066mhz?

http://www.newegg.com/Product/Product.aspx?Item=N82E16820220423
Click to expand...

Right. Sounds like a good choice as well... except the CAS rating is 9 vs 7 for the others. However, the SPD may be programmed for 1066 CAS7 on these anyway, although CAS8 is more likely. Unfortunately, you won't know until you try if the lower timings will appear. If you try these, please report back with your findings. If you can return them, there's no harm in trying.
 
VirtualRain said:
Right. Sounds like a good choice as well... except the CAS rating is 9 vs 7 for the others. However, the SPD may be programmed for 1066 CAS7 on these anyway, although CAS8 is more likely. Unfortunately, you won't know until you try if the lower timings will appear. If you try these, please report back with your findings. If you can return them, there's no harm in trying.
Click to expand...
Is there a utility for OS X that allows a user to set the CAS timing data in EFI ('09 model of course)?
 
nanofrog said:
Is there a utility for OS X that allows a user to set the CAS timing data in EFI ('09 model of course)?
Click to expand...

No. Not that I'm aware of.

I was supposing that the memory SPD table might be programmed with a range of speeds and CAS timings. For example, memory rated for 1333 at CAS9 may also have an entry in the table for other JEDEC speeds such as 1066 at CAS8, but that assumes the memory passed QC at CAS8 at 1066. No way to know what the SPD is programmed with until you fire it up.

As far as verifying what the CAS is, I'm not even sure there is a utility for OSX that will read the SPD or EFI... is there? If not, then you will have to use CPUZ under Windows to see what's going on.
 
VirtualRain said:
No. Not that I'm aware of.

I was supposing that the memory SPD table might be programmed with a range of speeds and CAS timings. For example, memory rated for 1333 at CAS9 may also have an entry in the table for other JEDEC speeds such as 1066 at CAS8, but that assumes the memory passed QC at CAS8 at 1066. No way to know what the SPD is programmed with until you fire it up.

As far as verifying what the CAS is, I'm not even sure there is a utility for OSX that will read the SPD or EFI... is there? If not, then you will have to use CPUZ under Windows to see what's going on.
Click to expand...
I'm not aware of any utility similar to CPU-Z for OS X, nor was I sure that the system could be manually adjusted or not (SPD table).

A utility would be easier, but so long as a manual means is possible, whom ever figures it out can post the proceedure to assist others that want to do this as well. :) Options are nice. ;)
 
For the vast majority of users, the difference between populating 3 memory slots vs. 4 will not result in a discernible performance difference. Most benchmarks appear to point to a 3-5% RAM performance penalty when you go to 4/8 DIMMs, which is not something anyone really needs to worry about. For those who want that 3-5% RAM performance back while using 4 DIMMs can replace their Quad Xeon with an equivalent Core i7 processor without ECC support. You get back that 3-5% performance when you don't have ECC overhead to deal with.
 
AZREOSpecialist said:
For the vast majority of users, the difference between populating 3 memory slots vs. 4 will not result in a discernible performance difference. Most benchmarks appear to point to a 3-5% RAM performance penalty when you go to 4/8 DIMMs, which is not something anyone really needs to worry about. For those who want that 3-5% RAM performance back while using 4 DIMMs can replace their Quad Xeon with an equivalent Core i7 processor without ECC support. You get back that 3-5% performance when you don't have ECC overhead to deal with.
Click to expand...
Odd way to go about it, but it would work. :p

ECC's overhead isn't much to worry about anyway, and most usage does just fine in dual channel mode, which is what the system falls back to when you populate the 4th DIMM per processor. Unless the system is a server, not really anything to worry about right now. Down the road, maybe, assuming the software catches up before the machine is too old to serve it's current purpose. ;)
 
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