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rcarlos243
09-13-2015, 02:11 AM
Download CPU-Z: http://www.cpuid.com/softwares/cpu-z.html


Under CPU-Z click SPD.

There should only be 2 module occupying the slots. If there is 3 modules you need to remove or add 1 DIMM to make it run in true Dual Channel mode.


My FPS went from spiky and stuttery to buttery smooth on my OC'ed panel.

InfernoStorm
09-13-2015, 03:11 AM
Wow that's pretty cool, thanks for sharing!

challenger1
09-13-2015, 07:23 AM
Mine already had 2 and 4 slots used. Dang!

Edweird
09-13-2015, 08:31 AM
Generally speaking, Intel FLEX tends to take care of mismatches - I don't see any difference between 2x8 (16) and 2x8 + 1x4 (20).

But if it works for you, great. CPU-Z reports dual channel either way and benchmarks seem to reflect no real difference. Were your modules all the same?

Usually, FLEX takes the bottom part - in this case the lower 4 GB of all 3 modules - and runs that in dual channel, the rest runs at single channel. This is what is known as asynchronous dual channel (sadly our laptops don't support triple or quad channel) and to my knowledge it is better than single channel but worse than pure dual channel. However, 3 8GB modules in async dual channel seems to always be better than just 2 8GB modules on full dual channel - or at least that's what I'm getting from reading around.

To me it sounds like one of your modules was defective.

rcarlos243
09-13-2015, 09:57 AM
I am more than 100% sure the DIMMs are not defective and it is not the first laptop I have that exhibits the same performance characteristics when 3 DIMMS are present on the system.

CPU-Z do report it is running at DUAL Channel with 3 DIMMS but it is not actually running in Dual Channel Mode.

You can verify it by running AIDA64 Cache and memory benchmark and compare the result with True Dual Channel mode (with 2x dimm or 4x dimm).

Nader
09-13-2015, 10:54 AM
I don't quite understand what you mean. Do I need to go to SPD tab?

Nader
09-13-2015, 10:57 AM
If you mean Ram I have 2 Slots occupied and 2 slots un occupied.
You suggest adding Ram to one Slot or Removing 1 (if I have 3)?

rcarlos243
09-13-2015, 11:04 AM
If you mean Ram I have 2 Slots occupied and 2 slots un occupied.
You suggest adding Ram to one Slot or Removing 1 (if I have 3)?

If there is 3 physical memory out of 4 slots, true dual channel mode will not work and you will suffer from FPS dps and poor consistency.

To run true dual channel mode you need to have either 2 physical memory out of 4 slots OR 4 physical memory out of 4 slots.

If you have 3 physical memory and want to run true dual channel by removing 1 physical memory, make sure the remaining 2 are on the same slots (either both at the bottom cover or behind the keyboard).

Nader
09-13-2015, 11:23 AM
Well that seemed to be the problem with people having more than 16 GB Of Ram (I have slot 2 and slot 4 occupied so I don't think I need to do any thing on my part).

could you tell us the improvement you had through this and what fps you were getting and now you have?

Edweird
09-13-2015, 12:31 PM
That's not supposed to happen. Various websites claim that if this happens it's due to lanky synchronicity between the RAM and CPU. In a normal case scenario, you shouldn't be seeing any of these issues. I've gained a few FPS by going from 8/4 to 8/8/4 with the 2 8 gig modules in the corresponding slots.

I'll have a detailed look through what does what, but like I said, FLEX is supposed to distribute the memory into sections and force asynchronous dual channel, which is why CPU-Z reports it as such. Not the whole memory is running in dual channel then but if any issues arise it would be because of lack of compatibility or crap interaction.

EDIT: Okay, I ran AIDA64 memory benchmarks. I use standard Hynix memory.
8/8/4
Read: 23463MB/s
Write: 24958MB/s
Copy: 23009MB/s
Latency: 71.1ns

8/8
Read: 24051MB/s
Write: 25092MB/s
Copy: 23200MB/s
Latency: 72.9ns

Okay...that doesn't tell me much. If anything, I gained a couple hundred MB from the memory controller being offloaded and the dual channel covering the full 16GB (the +600MB/s to read speeds is nice but impossible to notice). There's nothing here to show that 2 is much better than 3 for me, at least not in the way you describe. Latency even went up...

Then again, the i7-4710HQ + GTX980M combo beats the **** out of any game you throw at it (except maybe Star Citizen on Very High) so it's kinda hard to determine any performance differences.

To put things into perspective, here's the scores for a single 8GB module:
Read: 12405
Write: 12551
Copy: 12304
Latency: 67.7

So, the difference is minimal and I'll underline again, if there's issues, they're gonna be because of lack of synchronization. Sadly, I can't confirm your theory either way since I don't have your issue.

Still, it's nice to see that dual channel actually DOES make things literally twice as fast.

aeolisio
09-14-2015, 03:51 AM
Download CPU-Z: http://www.cpuid.com/softwares/cpu-z.html


Under CPU-Z click SPD.

There should only be 2 module occupying the slots. If there is 3 modules you need to remove or add 1 DIMM to make it run in true Dual Channel mode.


My FPS went from spiky and stuttery to buttery smooth on my OC'ed panel.
Thats not how a g751 or intel flex memory works. Like Edweird said you can have odd numbers of stick it will run in flex mode which is dual channel for the pair and the 3rd stick will run in single channel mode. That does not affect the dual channel speed but any noticeable amount. I am guessing you had mismatched ram or a defective stick or maybe you didnt use a repeatable test.
https://en.wikipedia.org/wiki/Multi-channel_memory_architecture
http://www.intel.com/support/motherboards/desktop/sb/CS-011965.htm
Please be careful of spreading the wrong information. What if 20 users who didnt bother to research followed your advice and removed their third stick only to figure out months later that you were very wrong after they had sold that stick because they assumed you had actually done the research.