would one 8GB stick of RAM be o.k. for 6-core?

[Umbongo]

I tested the 3.33GHz 6-core with two different memory configs. Then I ran a 64 bit memory stress test.

4x8G = 32G = 10.5 GB/s
3x8G = 24G = 14.3 GB/s (or 36% faster)

However, when I ran After Effects CS5 project render using 12 cores and 1.5G per core, the 32G config took 72 sec, the 24G took 71 sec. In other words, if there is a difference in real world performance, you would need a stopwatch to detect it.

Why? Because few if any real world apps use the full memory bandwidth. I'm still testing. If I find any app that benefits from the 3 stick "triple channel" config, I'll report it here.

I'm interested in seeing some memory speeds for six and eight 8GB DIMMs on a dual processor system if you could do that. Eight 8GB DIMMs should not be able to run at 1333MHz as they are registered rather than unbuffered. While it won't much matter to anyone who needs that much memory, it would be nice to have it recorded from a respected source.

edit: Actually I'm wondering if four 8GB RDIMMs knocks the speed down to 1066MHz too on the single processor system.

 

[GoogleFish]

I am running a Quad 3.2 with 1 stick of 8GB from OWC.

No problems at all.

(In fact when I first booted it up after taking out the 3 1 GB sticks and replacing them with my 1 8GB stick I got a message saying that my RAM was installed in the proper slot.)

The 3 X 1GB sticks will not work with the 8GB? So a 4GB stick will also not work with the stock 1GB sticks?

 

[Umbongo]

The 3 X 1GB sticks will not work with the 8GB? So a 4GB stick will also not work with the stock 1GB sticks?

8GB DIMMs are a different type, they are registered ECC. They won't work with unbuffered ECC. 1, 2 and 4GB DIMMs from Apple, OWC, transintl., Kingston etc for the Mac Pro are unbuffered.

 

[milo]

The 3 X 1GB sticks will not work with the 8GB? So a 4GB stick will also not work with the stock 1GB sticks?

It depends on the specs of the 4 gig stick, seems like some are, some aren't. Check with the vendor.

 

[MacSince1985]

I think it's very risky to buy 8 gig chips with the intention of adding more later. The 8's seem to be extremely particular about what they are used with - if you don't buy all the 8's at the same time, there's a chance they may not play nice together, making one or more of them unusable. Chips bought later may list the same specs but still not be compatible, it happens sometimes.

I believe OWC's lifetime warranty covers that situation and would let you exchange the incompatible chips any time. All you'd pay for is the return shipping.

 

[Xorgo]

Similar question - hoping to eventually get to 48GB using 6x8GB on a 12-core Mac Pro but want to do it in two steps - would it be ok to do 3x8GB on one CPU and move stock RAM 4x2GB on other CPU? thanks for all the info!

 

[davidp158]

incremental RAM upgrades

I am curious about incremental RAM upgrades, too. I have a 6-core on order, and I intend to buy 12GB (4x3GB) of RAM.

Do the 8GB RAM sticks work alongside 4GB RAM sticks? When I can afford to, I was hoping to pull one of the 4GB sticks and using the available 2 RAM slots to add 16GB (2x8). If pairs of the 4GB and 8GB RAM sticks can't be used in the 6-core, I'm tempted to buy a pair of 8GB sticks and hope OWC's future 8GB RAM sticks will play nicely with them.

4x3=12GB RAM ($515 OWC's current price)
8x2=16GB RAM ($739.98 OWC's current price)

BTW, OWC's web page with RAM prices doesn't show an 8x2 configuration for the single processor (4 & 6 core) machines, but they do show an 8x2 configuration for the dual processor (8 & 12 core) machines. Any reason why 8x2 RAM configuration would not work with the 6-core?

http://eshop.macsales.com/shop/memory/Mac-Pro-Memory#1333-memory

Similar question - hoping to eventually get to 48GB using 6x8GB on a 12-core Mac Pro but want to do it in two steps - would it be ok to do 3x8GB on one CPU and move stock RAM 4x2GB on other CPU? thanks for all the info!

 

[milo]

I believe OWC's lifetime warranty covers that situation and would let you exchange the incompatible chips any time. All you'd pay for is the return shipping.

That's good to hear. And a good reason to stick with companies that have that sort of policy. Thanks for the info.

 

[CrazyFingas]

Geez....this is going to make me want to populate my dual processor system 1 8GB at a time all the way up to 48 GB.....the insanity!!

Would this be a good/bad idea?

 

[2contagious]

Would this be a good/bad idea?

Apparently it will work (up to 32GB for single processor configurations, up to 64GB for 8 core and 12 core), but only starting with 1 stick of 8 GB RAM will limit the memory bandwidth ('diglloyd' claimed 1/3 of max. bandwidth. He tested the 6 core with 1, 2, 3 and 4 sticks of 8GB RAM from OWC), so I guess it's possible, but it's better to start off with two sticks of 8GB RAM.

 

[johnnymg]

Apparently it will work (up to 32GB for single processor configurations, up to 64GB for 8 core and 12 core), but only starting with 1 stick of 8 GB RAM will limit the memory bandwidth ('diglloyd' claimed 1/3 of max. bandwidth. He tested the 6 core with 1, 2, 3 and 4 sticks of 8GB RAM from OWC), so I guess it's possible, but it's better to start off with two sticks of 8GB RAM.

He also stated that the 'real-world' difference was negligible.

JohnG

 

[2contagious]

He also stated that the 'real-world' difference was negligible.

JohnG

Wasn't he talking about the difference in performance between 1066 and 1333 MHz sticks?