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I have motherboard with 6 memory slots, 3 green, 3 black, grouped in 3 pairs black+green. There are two setting in BIOS which are seem to me as related to this:

Channel Interleave Setting
This function is allows you to select the Channel Interleave Setting. The
options are 1 way, 2 way, 3 way, 4 way, 5 way and 6 way.

Rank Interleave Setting
This function is allows you to select the Rank Interleave Setting. The options
are 1 way, 2 way and 4 way.

Can you please explain how these settings are work?

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3 Answers 3

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Channel Interleave:

Higher values divide memory blocks and spread contiguous portions of data across interleaved channels, thereby increasing potential read bandwidth as requests for data can be made to all interleaved channels in an overlapped manner. For benchmarking purposes when using three memory modules, a 4-way interleave may surpass the scoring performance of setting 6-way interleave depending on the benchmark and operating system used (32-bit vs. 64-bit). We did find however that a 6-way interleave was capable of a higher overall BCLK for Super PI 32M than using a 4-way interleave setting (unless of course you run single- or dual-channel and appropriate channel interleaving thus decreasing load upon the memory controller).

Rank Interleave:

Interleaves physical ranks of memory so that a rank can be accessed while another is being refreshed. Performance gains again depend on the benchmark in question. For 24/7 systems using triple-channel memory configurations there is no advantage to setting this value below 4 while Channel Interleave should be left at 6 for best overall system performance.

Since you have 6 memory modules you want to use 6-way and 4-way for the respective values.

Source

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To have a bit more of a practical answer. I ran into this using a dual CPU server board with 18 ram slots. Its an older server (2010) I got really cheap with a total of 72GB RAM (triple slot channels DDR3).

When I installed Windows Server it said I only have 24GB usable? (but 72 installed?)

In the BIOS (default settings)

  • Channel Interleave = 6
  • Rank Interleave = 4

So I changed everything to:

  • Channel Interleave = 1
  • Rank Interleave = 1

All the memory showed up as usable but it was very slow. The logon process was much slower and the UI was laggy.

Then tinkered with it like this

  • Channel Interleave = 6
  • Rank Interleave = 1

Usable RAM = 72GB

The logon process was fast, the UI was quick and it was running normally.

Channel Interleave (From reading about it and looking in the manual it seems like) is the how many channels it should run at. Since I have Triple Channel Slots and I want it to run in Dual-Channel Paired DDR3 I need to keep it at Chanel Interleave 6. 6 dived by 3 = 2 - So the North Bridge has two channels per stick. Very strange way of presenting that.

Rank Interleave as I understand it, in layman terms is like "Mirroring or caching" the RAM Zones. So when its set to 1 I have accesses to all RAM but I/O access is the normal speed per channel. When we start to increase this it starts to use other RAM ranks (one side of a RAM stick is called a rank and can be accessed by 1 channel by the dual channel configuration (and in a tripple channel slot configuration thats why you need it to be 6 so its 2 channels per stick, 1 channel per rank) So "I think" the RANKS are mirrored onto other physical RANKS increasing the I/O. Essentially if I have 800Mhz Dual Channel and I increase this, I am dropping the physical usable RAM down but increasing I/O by a factor of some sorts. Setting this to 4 splits all 18 ranks by 4 (4.5 ranks which is 2 1/4 physical stick ACTS as ONE Stick (and since you cant divide a stick into a quarter I think it just goes with 2 - hence why I see half the amount of RAM) This essentially can turn 800Mhz RAM into "1600Mhz" in the North Bridge, more than doubling the IO speed at the cost of usable RAM.

So the quote in the answer above saying it has no advantage setting below 4, well for me I prefer more RAM for virtual machines.

Maybe on Gaming boards that is different ?? But on the server board I tested it and it runs that little bit faster on the default settings, but since this is going to be a very low used

  • NAS (FreeNAS especially prefers more RAM over speed of RAM - So I can just give it 32GB and enjoy massive speed improvements on SAMBA compared to my 4GB current system)
  • Router (hardly needs anything much but since I got all the extra I can just squid cache into RAM!)
  • Virtual Machine playground (mostly going to be Ubuntu Server... which is fast on a Raspberry Pi)
  • To show off.. because I never owned this much RAM and nobody is gonna ask how at how many rank interleaves it is running at.

This is just my understanding - if you read this and I am totally wrong please let me know. I did try and read various sources and try various things my self - and I just used my common sense to work this out

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You could try shoving four of your 6 new memory modules into paired slots and changing the channel interleave to 4 way, but this may compromise system stability. I thoroughly recommend getting the right tools for the job (6x triple-channel DDR3-1600) and leaving the bios settings on auto for interleaving. If you wish to overclock, the primary timings should be altered - by small amounts.

Hope this helps. :-D

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    He already has 6 DDR-1333 memory modules. This also does not explain what these settings are used for or what the values should be.
    – Ramhound
    Commented Jun 12, 2013 at 15:59

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