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Single-sided vs Double-sided and 64Mx16 vs 32Mx8

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August 8, 2004 12:37:16 AM

I'm working on an upgrade to an Athlon 64 by way of an MSI K8T Neo motherboard. I bought a Corsair PC3200 512MB stick (model VS512MB400) to go with it. The motherboard manual shows a table with preferences for single-sided versus double-sided memory and the specific DIMM-slots on the M/B where they should be placed. I haven't seen anything on my RAM indicating that they are single- or double-sided, though the DIMM physically has ICs on both sides of the module. I seem to remember reading that people often say double-sided when they mean dual-bank. If that's the case, I may have a problem. My M/B manual states that when all three slots are filled with PC3200, all of the RAM should be single-sided. Corsair doesn't show specs for this on Value Select memory, but the XMS series always seems to be dual-bank, so maybe it's true of the Value Select series, too. If so, what problems can I expect in the future when I upgrade to fill all three slots with double-sided memory? Will I have speed problems? Stability problems? A non-booting system? I don't even know for certain that double-sided and dual-bank mean the same thing. Help.

Also, while I'm asking questions about obscure RAM specs, what, if anything, is the real-world difference between 32Mx8 DIMMs (such as the Corsair CMX512-3200) and 64Mx16 DIMMs (such as the VS512MB400)? I remember about a decade ago, regarding 72-pin SIMMs, companies would offer 3-chip versions and 8-chip versions, but it was never clear to me which was better or why, or if the two types were compatible. Maybe someone can clarify.
August 9, 2004 2:18:10 PM

Double-sided means having chips on both sides of the simm.

I don't know what that means in reference to you having problems or not. AFAIK, some may have problems, some may not, but I have no specific info. (not to say someone more experienced than me won't have specific info)

Unless things have changed (as in, my more technical info comes from the time prior to 72-pin simms, when they were really single chips you inserted into sockets...) The only difference between the different chip densities is the number of actual transistors on the chip, and the matrix method used by the controller or on-simm circuitry to access it.

There may be a difference at the motherboard level, but I don't think so.

Dual bank is a term I don't have a definite def. for, although I think it used to be used to define the ability of a mobo to interleave memory access for performance... Hopefully someone can confirm/deny that and give us both an education...

Mike.
August 9, 2004 5:39:25 PM

- VS512MB400 is two-rank (double-sided) dimm.

- Running 3 unbuffered two-rank dimms with this processor would not be suggested because of performance and/or system functionality reasons.
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August 10, 2004 6:58:40 PM

Memory modules on both sides or one side makes no difference. Your motherboard actually sees RAM in "banks", basically areas of RAM to write to. Dual-banked means the RAM actually takes up 2 banks. This is important because sometimes a mobo with 3 DIMM slots only has 5 banks. So one of the DIMMS has to be single-banked, or the mobo won't be able to see the whole DIMM (the DIMM is programmed to have half it's capacity in each bank, so 1/2 the RAM is unaccessable in the 6th bank, which the mobo doesn't have). However, memory specs aren't always accurate. You should do some research and see what people have actually ben able to run on your board.

"It's too late now anyway. That song is stuck in my head and the only way to get rid of it is to blow it out. With a bullet!! - Carl
August 11, 2004 6:00:09 AM

In response to fishmahn's last comment about dual-bank, I think you're right that dual-bank refers to an interleaved on-DIMM configuration that allows a performance enhancment similar to the way RAID 0 (striping) provides extra performance for hard drives. The motherboard (M/B) does have to support it (most do), but it shouldn't be confused with dual-channel support, which is a M/B feature that interleaves access between two different memory modules. Dual-channel is now available in the latest 939-pin Athlon M/Bs, but not on the 764-pin versions.

With more research, it appears that the terms double-sided, dual-bank, and double-rank are all used interchangably in the real world, regardless of what their original meanings might have been. It also appears that double-rank versus single-rank is an important specification for memory to be used in Athlon 64 systems. I found a THG article page at http://www.tomshardware.com/motherboard/20040602/memory... that shows the exact same chart as my M/B manual for the MSI K8T Neo. I mentioned this in my original post and this chart was what made me begin to dig into this topic. Also, I noticed that some single-rank DIMMs are available for purchase, so there really is a decision to make as a consumer. Another bothersome thing worth mentioning is that the retail store where I bought the M/B claims that it supports 3GB. The M/B says 2GB max. The THG chart suggests that it would support 3GB, but not at PC3200 speeds. Can anyone explain what's up with this? Do 1GB single-rank DIMMs exist yet? I'm trying to avoid the situation where I have to pull old RAM out of my system when I upgrade some time down the road.
August 11, 2004 6:15:57 AM

Oh, and here's the real kicker. On the page in the MSI M/B manual preceding the notorious chart, MSI states, "Memory modules can be installed on the slots in any order. You can install either single- or double-sided modules to meet your own needs." The chart that follows is titled, "Recommended Memory Combination List." So if I can install them in any order and with any type, then why do I need configuration recommendations? So that's why I start to wonder if performance issues come into play here.

Attention all memory experts, please report to the front of the building...
August 11, 2004 2:50:35 PM

- All of the 1GB dimms that i'm aware of are double-rank.

- If a 3-dimm double-rank dimm configuration can be done successfully, i would guess that it would be best to set the command rate to 2T (available for CG or later revision of Athlon64) and decrease the memory clock.
August 12, 2004 12:24:43 AM

My MSI Master2 manual has the same thing in it but the table had the titles (dual channel - 128 bits) and (single channel - 64 bits)... which i would think is talking about dual channel ram and don dual sided ram.. though yours could be different i guess
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