Question about Dual Channel memory mode

[The Outsider]

On my mb there are four ram slots and I've got two currently populated
with 2x 512mb sticks of Samsung ram and it is running in Dual Channel
mode.The questions is that if I want to keep it running in DC mode and
populate the other two slots does the ram have to be the same as what
is already installed or can the timings be different? I was planning
on getting another two 512mb sticks of Samsung ram but what I see
available at my supplier has different timings than my current Samsung
ram.

 

[Jim]

Using different timings in the other DC pair shouldn't affect your ability
to run DC. I recently had 2 x 512mb of Kingston HyperX PC32000 (KHX3200AK2,
2-3-2-6-1) installed in DC mode. I then added 2 x 512mb of HyperX PC4000
(KHX4000K2, 3-4-4-8-1). Didn't affect DC at all, the system continued to
function in DC mode as before.

If you think about it logically, there's no reason to expect otherwise.
Your motherboard will ALWAYS setup the timings to the LESSER of the DC
pairs. And since most memory can still run effectively with slower timings
(within reason), the net effect is, BOTH DC pairs *are* running at the same
timings!, regardless of whether each pair has the POTENTIAL to run at
different timings. IOW, the very nature of how memory is configured
virtually guarantees you'll NOT have a problem.

The real problem is when WITHIN a DC pair you have different timings. The
memory controller in that pair typically has less tolerance for such
differences. Actually, I've heard of cases where even within a given DC
pair, one stick was *slightly* different from the other, and yet DC was
enabled. I believe the need for IDENTICALNESS (is this a word?) is a little
exaggerated. But to avoid headaches, it certainly makes sense to use
IDENTICAL sticks whenever possible. But once you're talking across DC
pairs, at least my experience has been, it doesn't matter. In the case of
my HyperX PC3200 + PC4000, my system simply setup my motherboard to PC3200,
2-3-2-6-1, and all was fine, DC nirvana.

HTH

Jim

 

[dawg]

Will any motherboards run in DC with 4 DIMMs?At 200FSB? I think you have to
sacrifice FSB to 166 to run 4 DIMs.

 

[Ann]

Will any motherboards run in DC with 4 DIMMs?At 200FSB? I think you have to
sacrifice FSB to 166 to run 4 DIMs.

Some motherboards definitely drop down to 166 when 4 sticks are used
but I don't know if they all do. The OP should read the motherboard
handbook to see what happens in his case.

Ann

 

[The Outsider]

Using different timings in the other DC pair shouldn't affect your ability
to run DC. I recently had 2 x 512mb of Kingston HyperX PC32000 (KHX3200AK2,
2-3-2-6-1) installed in DC mode. I then added 2 x 512mb of HyperX PC4000
(KHX4000K2, 3-4-4-8-1). Didn't affect DC at all, the system continued to
function in DC mode as before.

If you think about it logically, there's no reason to expect otherwise.
Your motherboard will ALWAYS setup the timings to the LESSER of the DC
pairs. And since most memory can still run effectively with slower timings
(within reason), the net effect is, BOTH DC pairs *are* running at the same
timings!, regardless of whether each pair has the POTENTIAL to run at
different timings. IOW, the very nature of how memory is configured
virtually guarantees you'll NOT have a problem.

The real problem is when WITHIN a DC pair you have different timings. The
memory controller in that pair typically has less tolerance for such
differences. Actually, I've heard of cases where even within a given DC
pair, one stick was *slightly* different from the other, and yet DC was
enabled. I believe the need for IDENTICALNESS (is this a word?) is a little
exaggerated. But to avoid headaches, it certainly makes sense to use
IDENTICAL sticks whenever possible. But once you're talking across DC
pairs, at least my experience has been, it doesn't matter. In the case of
my HyperX PC3200 + PC4000, my system simply setup my motherboard to PC3200,
2-3-2-6-1, and all was fine, DC nirvana.

HTH

OK, thanks. It was my motherboards manual that got me thinking it
might not work as it said all four channels had to be populated by the
same ram. Or maybe I didn't read it clearly and it meant each two
slots had to be the same. Guess I'll bump up my ram to 2gb and try it
out.

 

[The Outsider]

Will any motherboards run in DC with 4 DIMMs?At 200FSB? I think you have to
sacrifice FSB to 166 to run 4 DIMs.

You sure about that? My mb manual doesn't say that is the situation.
If I have to drop from 200mhz to 166mhz I'll just stay with my current
1gb.

 

[The Outsider]

Some motherboards definitely drop down to 166 when 4 sticks are used
but I don't know if they all do. The OP should read the motherboard
handbook to see what happens in his case.

Ann

It doesn't mention it but I will look again to make sure.

 

[Jim]

Let's be clear here. As others have alluded to, yes, there can be other
issues wrt installing 2 vs. 4 DIMMs. Some older, first generation DDR
motherboards often had all kinds of restrictions. For example, your manual
might have indicated that the use of 2 DIMMs supports 400MHZ, but if you
installed 3 DIMMs, this dropped to 333MHz, and 4 DIMMs even worse, 256MHz.
In some cases, there were even restrictions on which slots you could use.
This was irrespective of dual channel. Heck, many of these early mobo's
didn't even support DC. The early days of DDR support were fraught with
many more compatibility issues than the prior SDR generation of memory, and
thus manifested in motherboards of that era.

So while people are making a legitimate point in their concern, it has
NOTHING to due with your specific question regarding DC. As always, you the
user have to consider ALL the issues regarding compatibility before making a
decision. This is assumed. All I was addressing was the specific issue of
DC support across DC controllers, that's all. As far as I know and have
experienced personally, differences ACROSS DC channels never caused a
problem, not with DC anyway. Beyond that specific issue, yes, it's always
possible there are other restrictions/issues having nothing to do w/ DC.

If you have a relatively current generation motherboard (I have an Abit AI7,
which is over two years old at this point, 4 DIMMs is not an issue, runs
400MHz no problem), it seems highly unlikely to be an issue. But as always,
check your user manual and note any precautions and act accordingly.

Jim