[CIA]

I have a 8 core 3.2 Mac pro, Currently it has 8GB of ram, (4x2GB). I still have the (removed) additional 2GB (2x1GB) Apple ram that came with the machine. I took the 2x1gb out because with the even number of matched sticks in the 4 slots, the MacPro memory runs in 256bit wide mode. I've been looking all over but can't find any mention if the banks work 8x4 or just 4x4.
If I re-install my 2x1GB apple sticks and bump it up to 10GB will it then drop out of 256 mode again or will the 4x2GB run in 256 while the other pair of 1GB sticks just run in normal 128 mode?
Does everything in the memory riser cards need to be fully matched for it to work in 256bit mode?

(This doesn't make much sense reading over my post, hopefully someone gets what I'm trying to say)


<EDIT> I found this which more or less answered my question </EDIT>

[tooki]

The early 2008 Mac Pros like to have every slot filled, even if the risers aren't matched. Put your memory back in to see an increase in your RAM performance, not a decrease!

[mduell]

Going from 4 to 6 or 8 slots filled increases memory bandwidth marginally, but also increases average memory latency, so the answer for you depends on what your apps are sensitive to. H.264 encoding, for example, I'd expect to be faster with 4 modules than 8 given its sensitivity to memory latency.

[gangster]

http://www.barefeats.com/harper3.html

The engineer they consulted under the "X" Factor section also implied there is a difference with Single (SR) and Dual (DR) Rank modules, with DR being preferred. I looked for memory deals on Newegg and found 4gb modules to be the best value but these are Quad Rank (QR-?) according to the Kingston site, think this is an issue?

http://www.ec.kingston.com/ecom/conf...VR667D2Q8F5/4G

[Simon]

Yep, make sure to fill up your memory slots.

And in the event that latency becomes a real issue for you, sell your MP and get a new MP with a much lower overall mem latency.

[gangster]

So, you are saying that the "QR" is good as long as I fill up the slots...?

Also, you imply, that the latency issue is so bad with FB-DIMMs that i shoudn't even bother to try to improve my last generation mac pro...?

Please explain.

Thanks

[Simon]

Originally Posted by gangster 

Also, you imply, that the latency issue is so bad with FB-DIMMs that i shoudn't even bother to try to improve my last generation mac pro...?

No, you should definitely try to improve it. I'm just saying that if your workflow critically depends on mem latency you should probably consider swapping your MP for a newer model.

If I were you I'd do the actual benchmarking. Take a measure of your typical workflow with and w/o the extra memory. Find out what it means to you. Then decide on how to proceed.

[gangster]

Thanks Simon.

I just ordered the previous generation Mac Pro from B&H Photo for $2399 and am looking to populate the memory beyond 2gb. This link has been awesome because I had no idea how many issues there are between memory "types" within FB-DIMMs. As of now, I have ordered two 4gb Kingston modules that are Quad Rank (QR-?) and I guess I will add them to the existing 2x1gb (SR) modules.

These looked best:

http://www.newegg.com/Product/Produc...82E16820134875

[mduell]

That's not going to work well in a Mac Pro; it doesn't have the oversized heatsinks that the Mac Pros need due to their limited airflow. Pick one of these options.

Buy the memory capacity you need; don't worry about filling all the slots for an extra 0.5GBps memory bandwidth.

[goMac]

Also the Kingston ones you ordered are 667 mhz, which is going to give you a nice speed hit if you install those. You want the 800 mhz variety.

[gangster]

Fortunately, I did not order any memory that i couldn't cancel. I will pick the 800mhz vs. 667mhz speed when i order again Monday. Thanks for the help, I had overlooked the speed issue and focused on size only. As we all know, size doesn't matter!