Sniper 8gb and 4gb sticks NOT COMPATIBLE

[markw5252]

System:
windows 7 64bit pro
motherboard: MSI z68ma-ed55 (latest BIOS update - 1/9/13)
cpu: i7 2700k
ram:
G.SKILL Sniper Series 8GB (2 x 4GB) 1866 (PC3 14900) Desktop Memory Model F3-14900CL9D-8GBSR @ CL9-10-9-28 1.5v
&
G.SKILL Sniper Series 16GB (2 x 8GB) 1866 (PC3 14900) Desktop Memory Model F3-1866C9D-16GSR @ CL9-10-9-28 1.5v

The 2x8gb is the upgrade... I figured it'd all work fine because it's the same thing, just 8gb instead of 4gb. Apparently, that is not the case.
I can run either set on my mobo and it starts up, but I CANNOT run both sets at once.. It'll just sit with monitors on standby. (Before I updated BIOS, it would loop reboot)

I HAVE tried many different combinations-- setting DRAM settings manually, clearing CMOS, upgrading BIOS, but these two different sticks are NOT compatible on my system. any ideas??

[Tradesman]

ANY time you mix sets of sticks it can be problematic, even if they are the same exact model #. This is especially true with sticks 1600 and up, and mixing different densities (4GB/8GB or 2GB/4GB, etc) can be worse....Big thing here is XMP won't work, it's programmed by the packaged set and while the base timings are the same (9-10-9-28) the advanced timings will be different ...

With all the nay-saying out of the way, let's see what we can try and do to get them running (we might or might not, MSI hasn't put much into their Z68s) - you have the latest BIOS which is good, so let's start with the 8GB sticks in slots 1-3 from the CPU then manually ensure the base timings are right (the 9-10-9-28) and put them in manually (all 4 timings), make sure CR (Command Rate is 2T or 2N, start with the DRAM voltage at 1.57, set the MC (memory controller) voltage believe it's VCCIO or CPUVTT to 1.15, set VCCSA to 1.2, and don't know if you already have an OC on the CPU yet, but go ahead and set it to 39 or 40. Save and shutdown. Start back up and go into BIOS now go to the DRAM advanced timings and jot down what those are for future reference, in particular the
tWR, tRFC, tRRD, tWTR, tRTP, tCWL and tFAW, which are the ones we'll prob have to make adjustments to. Shutdown, add the 4 GB sticks and give it a try and let me know what it does, I'll be around for a at least a couple more hours

[markw5252]

OK, I set bios to defaults, set CPU ratio to 40, set dram frequency to 1866mhz, set dram timing mode to link, c9-10-9-28-2t manually, CPU core voltage auto, CPU I/o voltage 1.15, dram voltage 1.5655, system agent voltage 1.185. Everything else is defaults, still unresponsive when I add the 4 GB sticks. Also blue screens on windows startup.

[Tradesman]

Can you post up the advanced timings, and we'll see if we can tune it in

[markw5252]

yesh, for the 8gb sticks:
tRFC 243
tWR 14
tWTR 7
tRRD 5
tRTP 7
tFAW 24
tWCL 8
tCKE 5
tRTL 38

tRRDR 1
tRRDD 3
tWWDR 3
tWWDD 3
tRWDRDD 3

and this is what it shows for the 4gb sticks:
tRFC 155
tWR 15
tWTR 8
tRRD 6
tRTP 8
tFAW 29

[Techmeister]

It's worth noting that many RAM suppliers designate the RAM max advertised stable frequency based on the number of DIMMs being used when (2) or more DIMMs are in a kit rated at higher than 1333 MHz. This means that using more than one 2x/3x/4x kit that is rated for 1866 MHz., is not guaranteed to run @ 1866 MHz. Two of these kits may run fine at 1600 MHz. or more often at 1333 MHz.

The greater the number of DIMMs used and the higher the RAM quantity, the more difficult it is for the IMC to run error free. When you buy a matched set of 4-8-16-32 GB. RAM, these individual RAM kits have been confirmed by the RAM supplier to be capable of the advertised frequency for that specific kit. When you mix RAM kits even of the same rated frequency, all bets are off and all you can do is try for the highest frequency that the mixed set will run at, which often is below the rated frequency for the individual RAM kits - as noted by Tradesman.

FYI - Some BIOS also limit the RAM frequency to 1333 MHz. or lower when all DIMM slots are filled. With conflicting SPD boot data from mixed RAM kits, most BIOS will default to the lowest SPD frequency and latencies - if it boots at all.

[Tradesman]

markw5252

Let's try 9-10-9-31, 2T, tWR 15, tWTR 9, tRRD 7, tRTP 8, tRRD 7, tRTP 9, tFAW 28, tWTR 26, tRC 42 leave CPU I/o and system agent voltage as is, raise DRAM voltage to 1.6 (for now) and raise your vCore (CPU) voltage 0.03