Filling all three DIMMs slows down mem performance?

dscline

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Feb 14, 2000
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I've read in the past (can't find it right now) that going from memory in two dimms to three causes increased latency, and therefore slower memory performance. I have a Abit BE6-II BX MB, and have two 128M modules, one in slot 1, and one in slot 2. With the memory prices so low now, I'm tempted to get another 128M stick. Can anyone confirm that there actually is a memory performance hit when filling all three dimm slots?
 

Buddha Bart

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Oct 11, 1999
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can't say i've heard of any specific references to this.

On the other hand, it is known to possibly cause horrible instability. Especially if the sticks are different brands/timings. Not always, but often.

bart
 

dkozloski

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Oct 9, 1999
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Are we back to the old discussion of how much memory can be cached? Windows uses memory from the top down so if you install more memory than the cache can address, everything slows down because you're using uncached memory.
 

dscline

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Feb 14, 2000
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dkozloski, I don't think that's the issue here. I really wish I could find the original post that I saw this in. The way I intrepretted what I read was that it had nothing to do with the operating system or how it accessed the data in the memory, but more the way the chipset connects to the individual memory banks. It sounded like what was being said was for the chipset to access two more banks of memory (one more dimm slot) it had to slow down the timing to access all six banks vs. just four bannks (or 3 slots vs. 2). I haven't been able to find it yet, just trying to substantiate it (or disqualify it). Anyone ever heard anything like this, or have any knowledge about it?
 

PCResources

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Oct 4, 2000
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If you do not have a socket 7 Intel TX board, you will not have this problem, the problem there was that the (on board, not on chip) cache would not cache anything above 64MB.

There is simply no such problems with any chips having on-chip caches, they can adress as much memory as the CPU will allow.

So don't worry about it, you will not have any problems using that third slot.

And windows doesn't use memory "from the top and down" it doesnt access memory in any particular way, it just asks the chipset for the space needed, and recieves it.

Patrick Palm

Am speaking for PC Resources
 

thorin

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Oct 9, 1999
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If this were the case the price premium between 2x218Mb of RAM and 1x256Mb of RAM would be huge. Also consider who this would have affected server memory and performance when all that was available was 128Mb and 256Mb DIMMs (In a server that has .5Gb or 1Gb or more of memory when you can only build from 128Mb DIMMs there is any room for memory performance degradation).

You won't notice a difference if you add a third DIMM.

Thorin
 

dscline

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Feb 14, 2000
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FYI, I posted this same question in the forums at Tom's hardware. There is a user there named ZenOps that describes a situation that sounds like what I was reading before. For anyone interested, you can see that thread here
 

rahvin

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Oct 10, 1999
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<<You won't notice a difference if you add a third DIMM.>>

Of course you mean a BAD difference, right? ;)
 

thorin

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Oct 9, 1999
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Heh....no I really meant no difference at all. Your memory will not increase, you will see no benefit or degradation in the least.

Yes of course I meant no BAD difference.

Thorin
 

thorin

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Oct 9, 1999
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-----From Tom's:-----

Rambus's memory is extremely sensitive to this issue. The more sticks on the channel, the higher the latency.

With SDRAM this really shouldn't be an issue. An extra stick will change the electrical requirements in those slots.. so it is possible it will screw things up.. But not probible. The miniscule extra latency shouldn't be seen by the MB.
----------

Exactly. Only it isn't that the changes shouldn't be seen by the MB it's that they CAN NOT be large enough for the MB to see without causing major operational problems. Like the original problem that plagued the i820 chipset and delayed it's release, when Intel had to scale back the number of RDRAM slots you could include on a MB because the latency was to great for the Bus and CPU.

Thorin
 

PCAddict

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Nov 19, 1999
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Back in the old 300A/BH6 days, I remember reading that some BH6 motherboards acted kinda funky if you filled all of the slots. Mine has always worked fine with 384MB.

That's the only example I am aware of, other than the old Intel TX chipset issue that was covered already.