Triple Channel?

[macman21]

Call me crazy but are we all assuming the Nehalem Mac Pros can operate in triple channel mode based on the memory configurations suggested by Apple? I can't find anywhere on Apple's site or in the user manual that spells out the ability to run in triple channel mode. I know the integrated memory controller can operate in dual or triple channel mode. Being dual only would explain the number of memory slots. Can any owners of the new Mac Pros confirm triple channel operation? Or has anyone seen it documented one way or another by Apple? I'd love to be wrong...

[Tallest Skil]

It can handle any size of DIMM in any combination.

You can put in one, two, or three matched DIMMs, or no matched DIMMs.

[Frozengeek]

It can handle any size of DIMM in any combination.

You can put in one, two, or three matched DIMMs, or no matched DIMMs.

Would be nice to see some Nehalem benchmarks with two, three and four bays filled (or 4, 6, and 8 respectively).

[Daim]

So what will happen if i put in 4x2GB and only 2,5GB or are used in daily work. Will those be accessed in dual channel (slow) or trichannel mode (faster).

Sounds to me like the 6x1GB version will run faster when less memory (ie 2,5GB) is used because it's accessed in trichannel mode.

[Boneoh]

I should be getting my 16 gb ram in today.

I will benchmark first using 12 gb, then try it with 16 gb to see what the deal is.

[macman21]

I should be getting my 16 gb ram in today.

I will benchmark first using 12 gb, then try it with 16 gb to see what the deal is.

Excellent! Thank you.

[Daim]

I really would like to know how Nehalem handles 2x4GB.. like 2xdual channel or 1xtrichannel + 1xsinglechannel?

I wonder why noone asked this because it's the most important thing when deciding between 6x1 and 4x2GB

[JimGoshorn]

I should be getting my 16 gb ram in today.

I will benchmark first using 12 gb, then try it with 16 gb to see what the deal is.

Please do report back because that could be an important issue.

[Umbongo]

I really would like to know how Nehalem handles 2x4GB.. like 2xdual channel or 1xtrichannel + 1xsinglechannel?

I wonder why noone asked this because it's the most important thing when deciding between 6x1 and 4x2GB

Well it depends how you place them. Apple reccomends you go for two dual channel. You get the choice with 8 memory slots on the dual socket Mac Pros.

[macman21]

http://barefeats.com/nehal04.html

It looks like 12GB is better than 16GB, at least under the circumstances of Bare Feats' benchmark. This suggests the Mac Pro is forced into dual channel mode with all slots filled.

[VirtualRain]

Intel's own Core i7 motherboard uses the exact same memory configuration as the quad-core Mac Pro. You can read about the details in Section 1.5 of this technical overview...

http://download.intel.com/support/motherboards/desktop/dx58so/sb/e51290001us.pdf

There's likely plenty of memory benchmarks available for this board as well (but I don't have time to track them down).

http://www.intel.com/Assets/Image/prodlarge/dx58so_lg.jpg

The way it works is that memory installed in the first three slots (blue slots on the Intel motherboard) run in tri-channel mode with data interleaved across all three DIMMS. If a fourth DIMM is installed, it's obviously accessed in single channel mode since there's no other DIMM's to interleve the data across. However, it doesn't affect the interleaving taking place on the other 3 DIMMs.

Think of multi-channel interleaved memory as a RAID0 array of hard drives. To carry this analogy to the memory on the quad mac pro, you have three channels in RAID0 with an extra disk on it's own.

More info here... http://www.intel.com/support/motherboards/desktop/sb/CS-011965.htm

If Apple f'd this up, I'd be very surprised.