RAM CAS timing

[Brian Stirling]

Having lower CAS timing is better for performance but more expensive -- no surprise there, but how much real world improvement would one get going from 15-15-15-35 to 14-14-14-34 for something like the G.SKILL Ripjaws V Series 32GB (8GBx4 PC4-25600)? What about OCing?

System in question is based on an Asus x99-Pro/USB 3.1 motherboard using an Intel Core i7-5820K 6-core CPU with Corsair Hydro Series H100i GTX water cooler running Win10. My intention is to mildly OC to gain a bit of performance improvement without pushing reliability or noise.


Brian

 

[Carfax83]

Having lower CAS timing is better for performance but more expensive -- no surprise there, but how much real world improvement would one get going from 15-15-15-35 to 14-14-14-34 for something like the G.SKILL Ripjaws V Series 32GB (8GBx4 PC4-25600)? What about OCing?

System in question is based on an Asus x99-Pro/USB 3.1 motherboard using an Intel Core i7-5820K 6-core CPU with Corsair Hydro Series H100i GTX water cooler running Win10. My intention is to mildly OC to gain a bit of performance improvement without pushing reliability or noise.


Brian

Something like that would only show up in synthetic benchmarks. Haswell-E has a massive L3 cache plus a quad channel interface which makes fast memory practically useless truth be told. And no consumer application comes close to utilizing the bandwidth available anyway.

I speak as someone who has asked himself a similar question about two months back when I upgraded to a 5930K setup.

I went with 32GB G.Skill TridentZ DDR4 3200 CL16, but my PC hasn't benefitted from the high frequency memory at all. In fact, it wouldn't even run stable at DDR4-3200, and I had to downclock the RAM to DDR4 2666.. I did get it on sale though, so it's not all bad

However, running high frequency memory or very aggressive latencies on Haswell-E with large DIMMs can be pretty difficult, depending on how good the memory controller is in your individual CPU..

Like I said, mine won't run at DDR4 3200, without increasing the system agent voltage to an unsafe level. But DDR4 2666 is more than fast enough for Haswell-E.

In fact, you might find that DDR4 2666 CL14 is faster than DDR4 3200 CL16!

I have my RAM timings at 14-15-15-31 with 1T timing and it's rock solid stable. I've tried to put it at 14-14-14-32 and it was unstable..

But like I said, such a minor timing change would only show up in synthetic benchmarks so it's not a big deal..

 

[Dasa2]

14-14-14 vs 15-15-15 is small think of it like 0-25mhz cpu oc at a rough guess
only programs overflowing the l3 cache will benefit
games and z7ip are programs that will overflow it but not many games are cpu limited

below i have selected images from programs showing the largest gains if you check the links you will see that the programs are responding differently some see very little improvement from some changes

https://translate.googleusercontent...8.html&usg=ALkJrhgIBJc05UPrhDbSxvHI9DgS9Z5iCg

https://translate.googleusercontent...6.html&usg=ALkJrhh4l3RwXFMM-hvaJ3gzkjeiWuNWkg

https://translate.googleusercontent...7.html&usg=ALkJrhhE7SJVHNG7S-tTt0bvOHMUG3NByg

Channels 4\3\2

https://translate.googleusercontent...4.html&usg=ALkJrhiDNrJRHxJO850XfysIXJ0DPU6-Kg
this one is something to do with ram multipliers\dividers affect on performance with x99

 

[tweakboy]

No real world performance,,,, gl

 

[Brian Stirling]

So, if I understand this correctly, the Haswell CPU has enough cache to pretty much make RAM speed irrelevant -- is that right? If so, then any decent DDR4 RAM at even the slowest speeds of, say, 2400 would be imperceptibly slower than the same box running at 3200 with the same CAS timings. So, what's with the push for faster RAM if it's largely a non-issue?


Brian

 

[Dasa2]

its enough cache for some programs
but nowhere near enough for others

 

[Carfax83]

So, if I understand this correctly, the Haswell CPU has enough cache to pretty much make RAM speed irrelevant -- is that right?

Irrelevant is a too strong. Insignificant is a better description I think. Some programs do like the fast memory, like compression software for instance, as Dasa2's graph illustrates. But as for games, the difference is slight to nonexistent unless you're comparing a wide margin, ie DDR4 2133 to DDR4 3200..

If so, then any decent DDR4 RAM at even the slowest speeds of, say, 2400 would be imperceptibly slower than the same box running at 3200 with the same CAS timings. So, what's with the push for faster RAM if it's largely a non-issue?

Because many hardware enthusiasts want to have the fastest hardware regardless. And there are a lot of people out there that benchmark professionally. It's people like those that don't mind shelling out extra for faster memory, as it does make a difference in synthetic benches..

Plus faster memory can make a difference for dual channel rigs, since they have less bandwidth and less cache..

If you're a Haswell-E gamer though, I would say DDR4 2666 is more than good enough. That's the fastest speed memory you can use without changing the bclk strap I think, and still retain the use of adaptive voltage.

And keep in mind that you might not be able to run very high frequency RAM as the IMC on your CPU may not be able to handle it.....especially if you are using high density DIMMs like 8GB and greater..

 

[Brian Stirling]

No, I'm not a gamer at all -- my need is for video editing and I mean 4K video editing. Although there's overlap in the needs of gamers and video editing there are challenges with video editing not seen with gamers.


Brian

 

[BTRY B 529th FA BN]

tRFC makes a difference in my experience.