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Hello, I have a performance problem:
I have 4 same memory modules of:
8GB DDR3L 1600 CL11 1.35v Dual-Rank
with the i7-6700 processor.
In my B150 motherboard (Asrock B150M Pro4S/D3) if I use 2 Modules in Dual-Channel mode I get the expected performance, but not with all 4.
With 2 Modules (16GB) in dual channel "winsat mem" built-in windows 10 memory benchmark utility reports:
~22000MB/s
If I use all 4 modules (32GB) in dual channel mode "winsat mem" reports:
~15000MB/s
And just for comparison with 1 module in Single Channel mode:
~12000MB/s~
The performance difference is visible in various applications, not just that benchmark.
Is this a CPU limitation or a motherboard problem?
The processor documentation says that the skylake cpus has a total of only 4 memory rank controllers. Is this the reason for the performance degradation? All 4 modules have 8 ranks total.
Thanks.
NOTE: There are no stability/reliability problems in both cases, this is just a performance issue.
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Hello DSInt ,
Make sure you are using same memories with same speed, when using different speed DIMMs; the slowest memory timing is used. Also, I suggest you to contact your motherboard manufacturer to find out if your motherboard supports this configuration.
I can see at the AsRock website that only supports Dual Channel DDR3/DDR3L Memory Technology, but I recommend confirming this information with them.
Regards,
Ivan.
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Hello again,
As I already mentioned all 4 DIMMs are exactly the same. When only 2 of the 4 are installed in different channels (in any combination of the 4 parts) I get the expected performance.
I don't understand your comment about my motherboard supporting Dual Channel DDR3/DDR3L Memory Technology, also I have informed Asrock about the problem but they haven't replied yet.
Can you confirm if the 6th Gen core family processors only has 4 rank controllers? The documentation (datasheet) is not clear:
First it says in the System Memory Interface section:
"number of ranks per channel are SKU dependent", but I can't find anywhere the differences in SKUs.
And later in the DRAM Clock Generation section:
"Every supported rank has a differential clock pair. There are a total of four clock pairs driven directly by the processor to DRAM."
By comparison the 5th gen core datasheets clearly says:
"Up to 64 simultaneous open pages, 32 per channel (assuming 8 ranks of 8 bank devices)"
and
"The IMC supports a maximum of two DDR3/DDR3L DIMMs per channel; thus, allowing up to four device ranks per channel." which means 8 ranks total.
If that is the case, it can explain the performance degradation with 8 ranks total (as in my case), because of the slow rank switching.
Thanks.
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What I mean about Dual-channel, Triple-channel mode etc, you can see it here:
http://www.intel.com/content/www/us/en/support/boards-and-kits/000005657.html http://www.intel.com/content/www/us/en/support/boards-and-kits/000005657.html
When you have four RAMs installed, you will be doing Quad-channel mode.
Please check the DataSheet page 22 it explains the system memory organization modes:
http://www.intel.com/content/www/us/en/processors/core/desktop-6th-gen-core-family-datasheet-vol-1.html http://www.intel.com/content/www/us/en/processors/core/desktop-6th-gen-core-family-datasheet-vol-1.html
Regards,
Ivan.
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