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#265459 - 07/05/09 08:26 PM Re: Computer Build [Re: Ken.C]
Zimm Offline
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 Originally Posted By: kcarlile
Actually, as I understand it, as long as you have a minimum of 3 dimms, you're using 3 channel. I'm not sure how Intel's doing it, but there we are.


Right. So how do you get a 2GB, 4BG, or 8GB Dell setup unless they are using mismatched DIMMS (1 + 1 + 2)? I really only wanted about 8, but much easier to count to 13 by 3's than to 8 or 10. But I'm new to this...
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#265491 - 07/05/09 11:49 PM Re: Computer Build [Re: Zimm]
Ken.C Offline
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The 2 GB is undoubtedly 2 channel, but the 4 GB is potentially 1+1+1+1, and since it's minimum 3, Bob's your uncle.
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#265531 - 07/06/09 11:39 AM Re: Computer Build [Re: Ken.C]
Zimm Offline
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You lost me - and Bob - how do you get 1+1+1+1 in a 3 channel config? 1+1, then 1 and then 1? I didn't think you could mix and match like that. If so, I could pull out a 2GB DIMM and put in a 4, and have 4+2 and 2+2 and 2+2? Never heard of that, but I've only built one i7 system so I'm certainly no expert. But there are several articles that explain my understanding better than I can.
 Quote:
The three possible answers would be to use a cooling solution other than Supermicro’s, low-profile DDR3 memory modules, or simply three memory slots rather than six to populate the board’s triple channel configuration. Naturally, that'd be a problem for anyone looking to go over 12 GB, and even then, we're told that the the ICs needed for 4 GB modules are prohibitively expensive right now. It'd be hard to justify a move to 12 GB across three slots or 24 GB across six.

From the Tom's Hardware review at:SuperMicro X58 Review
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#265534 - 07/06/09 11:59 AM Re: Computer Build [Re: Zimm]
Ken.C Offline
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It's confusing, but Intel says you can have an uneven distribution and still use triple channel, as long as a minimum of 3 are populated. I'm not sure if they have to be the same size.

Also, I would take Tom's with a very, very large grain of salt...


Edited by kcarlile (07/06/09 12:00 PM)
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#265536 - 07/06/09 12:20 PM Re: Computer Build [Re: Ken.C]
ClubNeon Offline
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I'm not sure what happens in the case where one bank is full with 3 DIMMs, and the other isn't. I don't see how it would enable triple-channel memory access to all DIMMs in that case. Perhaps it does 3x to the first bank and single or dual to the second.

The motherboard manual says for best performance to populate all DIMM slots with same sized memory modules. That's what I'd say too.
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#265537 - 07/06/09 12:22 PM Re: Computer Build [Re: ClubNeon]
Ken.C Offline
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Well, there's 3 banks, to start with, 1 in each bank does triple channel. Add an additional 1 to a bank, and it apparently still does triple channel. My Gigabyte manual attests to this, and I've read it elsewhere as well--I believe in the review of the UD3P as well as reviews of the new Mac Pros.
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#265542 - 07/06/09 01:40 PM Re: Computer Build [Re: Ken.C]
Zimm Offline
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Registered: 12/08/08
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Loc: New Orleans
 Originally Posted By: kcarlile
It's confusing, but Intel says you can have an uneven distribution and still use triple channel, as long as a minimum of 3 are populated. I'm not sure if they have to be the same size.

Also, I would take Tom's with a very, very large grain of salt...


Interesting. Thankfully not something I have to worry about for some time.
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#265544 - 07/06/09 02:08 PM Re: Computer Build [Re: Zimm]
ClubNeon Offline
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From Intel's site:

* Triple channel mode is enabled when identical matched memory modules are installed in each of the three memory channels (blue connectors).
* If only two of the blue memory connectors are populated with matched DIMMs, dual channel memory is enabled.


Their example board has 4 DIMM slots. If all 4 are filled it operates in dual-channel interleaved.

It really does seem that a multiple of 3 matched DIMMs is needed to enable triple channel. An even number of matched DIMMs puts it in dual channel mode, anything else and it falls back single channel.

Don't confuse banks and channels. A bank is a grouped set of memory slots. On dual or triple channel boards a bank will have 2 or 3 slots respectively. Additionally, a mutiprocessor board will have nodes which are made of one or more banks. Each node is local to one processor.
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#265545 - 07/06/09 02:35 PM Re: Computer Build [Re: ClubNeon]
Ken.C Offline
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Gigabyte EX58-UD3R manual, page 16 indicates that 4 dimms does work with 3 channel. Very odd.
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#265546 - 07/06/09 02:48 PM Re: Computer Build [Re: Ken.C]
ClubNeon Offline
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I see what Gigabyte did. They put two DIMM slots on one channel, and the other two on their own. There will be some addressing contention between the modules on the shared channel if all four are installed. So there may be a slight loss in over-all throughput over using only 3 DIMMs. That trade-off needs to be weighed against the benefit of having more RAM available. Also it should be noted that the max bandwidth of 3 channel DDR3 isn't usually reached by normal workloads (i.e. non-benchmark programs), so the small loss probably won't be noticed.

Supermicro on the other hand built their board with 2 banks each having 3 channels. No shared channels within one bank.
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