performance - Memory Runs at Flex Memory Mode

08
2014-07
  • sammyg

    I had 4 GB RAM installed, running in dual channel mode.

    RAM: Corsair TWIN2X4096-6400C5DHX (CM2X2048-6400C5DHX)
Motherboard: Gigabyte GA-EP45-UD3R

Channel 0: DIMM1, DIMM2
Channel 1: DIMM3, DIMM4

DIMM 1: 2 GB, CM2X2048-6400C5DHX
DIMM 2: --
DIMM 3: 2 GB, CM2X2048-6400C5DHX
DIMM 4: --

    I added 2 GB more in DIMM 2. So now I have 6 GB in total.

    So this is the current configuration:

    DIMM 1: 2 GB, CM2X2048-6400C5DHX, channel 0
DIMM 2: 2 GB, CM2X2048-6400C5DHX, channel 0
DIMM 3: 2 GB, CM2X2048-6400C5DHX, channel 1
DIMM 4: --

    But now when I boot up, BIOS reports as running in "Flex" mode.

    a

    Why is that? The module I added is of the same brand and part number as the other ones that were already installed. From what I have read on the web, the "flex" mode only appears if you mix and match different module sizes, or different brand and part numbers.

    In fact, here is a quote from the motherboard manual about it:

    When memory modules of different capacity and chips are installed, a message which says memory is operating in Flex Memory Mode will appear during the POST. Intel® Flex Memory Technology offers greater flexibility to upgrade by allowing different memory sizes to be populated and remain in Dual Channel mode/performance.

    Here is a screenshot of a RAM report.

    b

    How do I tell if at least the original two RAM modules are running in dual channel? What do I look for?

    I notice that the module in slot 2 has a week/year parameter. While the original two do not. I don't think the date is accurate. But could this indicate that they are not same modules, internally? Like different revisions maybe?

    Why are there two different JEDEC frequencies? One is at 270 MHz and the other is at 400 MHz, why is that?

    This is what the DIMM slots look like:

    c

    Similar color means disimilar channel, and disimilar color means similar channel (in lack of a better way of expressing this idea). So yellow and yellow means channel 0 and 1, which makes up a dual channel. Similarly, red and red means channel 0 and 1. Colors are not an indication of channel (same color does not mean same channel), but a way to help install memory in dual channel mode. (Then you add the third wheel to the mix, like I did, and you're in this weird "flex" mode.)

    • Answers
  • Frank Thomas

    Your system is in flex mode because your channels are not of the same capacity. Since you have three chips but a dual-channel board/CPU flex is the best you can do. You must have an equal capacity on both channels to run full dual channel.

    in your case, it it probably best that way. the additional ram is likely worth the small degradation in speed from the flex channel interleaving. When you get the opertunity, drop another stick in to even it out.

    See more info about Ram channels and Flex mode here: http://www.intel.com/support/motherboards/desktop/sb/CS-011965.htm


    • Related Question

    intel core i7 - Triple vs. Dual Channel with 6 sticks of memory
  • WaldenL

    Assuming a Core i7 with a x58 chipset (IOW, triple-channel is supported)... I'm trying to decide if I need to buy triple channel memory kits. The MB has 6 slots, and I will populate them all. So I've got two options:

    1) Buy 2 triple-channel kits (3x2g sticks) identical kits

    2) Buy 3 dual-channel kits (2x2g sticks) identical kits

    Either way I have 6 identical sticks and 12Gig. And if the difference between dual and triple memory is in the controller, then I don't see the difference. Since I'm loading all 6 slots either way won't I end up with triple-channel access?

    Everything I've seen on the net talks about 2 sticks vs. 3 sticks, and obviously 2 sticks can't do triple channel. However, with 6 sticks I should be ok regardless of how I buy them, yes?

    FWIW, 12G purchased as 2 triple-channel kits will be ~$500, but 12G purchased as 3 dual-chanel kits would be $270. Big difference. Especially if I end up with triple-channel either way.


    • Related Answers
  • William Hilsum

    At one point, at wholesale, memory makers were changing designs by the week (well, month, but it felt very quick!), so if you bought in bulk from a supplier, even buying smallish quantities such as 10 sticks, you could get three or four different designs - it was a nightmare as dual channel (back then) didn't always work as some designs were to different (but the majority did work - you just had to find the right combination).

    Dual channel kits simply bypassed this as they "guarantee" compatibility.

    However, things seem to have settled down, and if you buy from the same company at one time, you usually do get the same sticks.

    If I was you, just buy whatever it takes to get the amount of memory you want the cheapest way - so go for the 3 dual channel kits, or even see if you can buy the memory as individual sticks as I have not run in to problems for the past few years.

  • MDMarra

    It's just marketing. If they are identical model numbers, the only difference is the packaging.