The AMD FX CPUs are rated by AMD to run up to 1866 DRAM at 1 DIMM per channel and up to 1600 with four DIMMs. This can be deceptive at both the upper and lower ends of their spectrum. I've seen and run a number of the upper-level CPUs with higher-frequency DRAM and seen many of the lower tier FXs that couldn't run the 1866 DRAM. This was one reason I chose 2400 DRAM as the test point. I fully expected to have to run the bulk of the testing at 2133, as I have seen very few FX CPUs that could handle 2400 DRAM, especially fully populated at 32GB. Pleased that I appear to have hit the lottery with my 8370, I believe that the Asus Crosshair V Formula Z may be another factor in the test system's exceptional stability. Higher priced than other AM3+ motherboards, I feel it's money well-spent.
Mixing Sets Of DRAM
Mixing sets of DRAM can be problematic, and this occurred with both the AMD Radeon DRAM and the ADATA sets. (Again, each sent two 2x8GB individual sets of DRAM, the first two 'sets' I tested with). Generally, the approaches taken to try and get mixed DRAM to play nicely can consist of timings and/or voltage adjustments. In the case of the AMD DRAM, it booted up fine and ran under the AMP settings until I tried to run Prime95, which promptly crashed. Raising the CPU/NB voltage (which runs the memory controller) by a slight + 0.06 increase stabilized the system. The ADATA sets didn't want to boot at all, but after a similar increase to the CPU/NB (+0.05), it booted and ran. Again, Prime95 was the nemesis, resulting in a crash. With this group of DIMMs, I raised the DRAM voltage to 1.7, and the CPU/NB another + 0.04, to achieve stability at 1.31. (Looking onward to the Intel build, I have little doubt that an actual four-stick packaged set of DRAM would have run without the additional adjustments.)
Without going into a bunch of boring details, I also tried mixing two sticks each from a variety of combinations of the DRAM available, with mixed results. I managed to get some to work together with voltage adjustments, two with timings adjustments, some with a combination of the two — and some combos just wouldn't work at all. In at least one case I tried with two Corsair sticks and two Team sticks, and they just wouldn't play at all — period! I then tried with the two remaining Corsair sticks and the same two Team sticks. That combination did play nicely. So it really goes to show that mixing DRAM is really a crapshoot; you never know if mixing sets/sticks of DRAM will play together.
Failure To Boot
Two of the sets wouldn't boot under DOCP at 2400 with all four sticks installed. I took another common tack with those sets and raised the CPU multiplier to 21.5 (raising the base frequency of the CPU from 4.0 to 4.3). Additionally, when this slight OC was applied to the ADATA DRAM, it allowed the DRAM voltage to be lowered back to 1.65, though the CPU/NB voltage still had to be maintained at a lowered level of 1.26.
Failure Under Stress
There were three cases of this in Prime95, and all three were solved with slight CPU voltage increases. So, it wasn't really caused by DRAM faults.
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Since the dawn of computer memory: Faster data rates=More access latency.Reply
It's great to see you getting the chance to do some articles on here, Tradesman1 Jim :)Reply
Interesting. I'll be coming back here several times over the next several months, as I save up for & consider options for a new computer. Good to know 2x 2 stick kits arn't nessicarily equal to a 4 stick kit, and annoying since I don't see many 4 stick kits in local online stores.Reply
Also good to know frequency has such a measurable impact on compression, I probably don't need fancy high freq ram but now I'm going to be more annoyed my budget won't allow it.
Thanks for the ponderous read! :)
This was such an eye opening read. Until now I though different ram frequencies really didn't amount to much. By those times in multitasking ? Wow.Reply
Thanks Tman. Looks like you really worked your butt off in this testing.Reply
Nope. Latency stays roughly the same while clock cycles speed up. DDR3-1333 CAS 6 and DDR3-2666 CAS 12 have the same latency in nanoseconds, the number of cycles doubles while each cycle occurs in half the time.15517997 said:Since the dawn of computer memory: Faster data rates=More access latency.
Pretty good review, made for a fun read. I'm still amazed at the ram incompatibility when mixing different sets. I know it exists, it's not the first time people have experienced this. I've mixed various ram just on a roll of the dice and I guess I've been lucky. The brand mixing was random. When upgrading one system from ddr2 to ddr3 I threw 2x2gb of patriot in with 2x2gb of geil evo one without issue. When upgrading one of these systems and adding ram, I added 2x4gb of team zeus at 1600mhz with 2x4gb of geil evo corsa at 1333mhz and just let the motherboard configure it and match to the lower speeds/settings. No issues with either.Reply
1.65V sticks on Z87/97 boards? I think the upper limit Intel mentioned in their white paper for Ivy and Haswell was something around 1.55 - 1.575V for DRAM voltage.Reply
Do what you want with your hardware guys, but I ll stay clear of these voltages.
I have 2 questions for future articles.Reply
1 - Why do memory control sugest no higher voltage then 1.65V yet my DRAM says it can handle up to 2.4V and why would they make a DRAM capable of handling 2.4V if no memory control can push safely over 1.65V? ( I'm runing on Kingston Beast 32GB 2400MHz )
2 - Why is there some DRAMs that are not compatible with some motherboards, what makes it compatible or not?
I would hate to risk shortening the life of an expensive Intel CPU by running more than 1.6V through its IMC. You raised it to 1.7??Reply