CAS Latency

[Peelingspud]

What would the performance difference between a CAS latency of 15 v 22 ?

I have an Asus Strix ROG Z270E motherboard and the current ram installed is Kingston HyperX Fury 2x8GB Dual channel (16GB total ) part number HX426C15FBK2/16 DDR4- 2666 CL15 and I am upgrading it to Crucial Pro 32GB Kit (2x16GB) DDR4-3200 • CL=22 • Non-ECC • UDIMM CP2K16G4DFRA32A as Crucial shows that memory is compatible with my system.
I have ordered the one Crucial kit for now to see if it works okay before getting another kit.

I was thinking it would not be a good idea to mix the current ram with the new ram as it's a different manufacturer and different size memory.

[Omega]

It depends, CAS is counted in clock cycles, so the impact on performance will also depend on memory clock speed.

22CL is pretty bad for a 3200Mhz kit. Are you sure you can't get another kit with CL 15/16? When I look at my local retailers the cheapest 3200Mhz kit is CL 16. All other kits in this price range are comparable with CL 16/17/18.

[_I_]

just find a kit that faster with lower timings than your current ram, and it will run at the slower speeds and higher timings

[nullable]

https://www.xbitlabs.com/ram-speed-calculator/

So for example
3200mhz DDR4 at CAS22 = 13.75ns
vs
2666Mhz DDR4 at CAS15 = 11.25ns

Which means the lower mhz RAM is actually faster due to its lower timings.

3200mhz DDR4 as CAS15 = 9.375ns, which is naturally faster than slower RAM at similar timings. But it's a lot faster than CAS22 DDR4 3200mhz. Which is why it's important to look at both, and not just go for the higher mhz RAM automatically. There may not be a difference

So for example in the case of

DDR4 3200mhz CAS18
DDR4 2666mhz CAS15 both end up with a 11.25ns. Not really gonna matter which one you pick performance-wise in most cases.

Overall you probably won't notice a difference most of the time, unless your use cases are highly sensitive to RAM performance.

[Peelingspud]

Thanks for the reply Nullable
That Crucial kit I posted is all I could find that is compatible, I cancelled the order for it as I am not sure if it's worth it.
So far I haven't found anything with a CL15 latency or similar for my system.
Reason I wanted more ram is I use that computer for recording and using samplers can use a lot of memory so more than my current 16GB would be nice.

[_I_]

3000 cl15 is really common
along with 3200 cl16
its harder to find ddr4 kits that are lower timings than those

[Peelingspud]

引用自 _I_：

3000 cl15 is really common
along with 3200 cl16
its harder to find ddr4 kits that are lower timings than those

Well I haven't found anything compatible with my system so far in Canada

[Omega]

引用自 Peelingspud：

引用自 _I_：

3000 cl15 is really common
along with 3200 cl16
its harder to find ddr4 kits that are lower timings than those

Well I haven't found anything compatible with my system so far in Canada

How do you mean compatible? Any DDR4 DIMM will work.

[_I_]

you can often swap speed for timings
lower freq may be able to drop cl by a tick or two

or just replace all ram in the system and enable xmp for the new ram

[Peelingspud]

So the big question is will that Crucial ram be ok , will I notice the difference ?
Amazon.ca won't let me cancel the order even though it hasn't shipped so looks like I will either go through the hassle of returning the ram or use it.

[_I_]

do your best to return it, and get something better

if you cant, use it, slow ram is better than not enough ram

[nullable]

引用自 Peelingspud：

So the big question is will that Crucial ram be ok , will I notice the difference ?
Amazon.ca won't let me cancel the order even though it hasn't shipped so looks like I will either go through the hassle of returning the ram or use it.

It'll work. My position is going to be that having enough RAM, even if it's not optimal or a little bit slower is preferable to not having enough RAM.

You probably wouldn't be able to tell as a user, the results would only be visible in benchmarks. And again, if you added it to your existing memory it would run at the "slower" speeds. And I'm betting that it'll run just fine at 2666 CL15 or worst you run it all at a bit higher CL16 or something.

It's not the end of the world. It won't cripple your PC. In most cases it's a semi-marginal detail. And there's plenty of RAM benchmarky articles covering these topics that highlight the differences. You're not running highend RAM anyway, adding more mid-rangey RAM isn't going to hurt you really.

And your system can run pretty much any DDR4 on the market. RAM is governed by standards (see JEDEC), and aside from extreme edge cases, the nice thing about strict standards is it virtually guarantees compatibility.

[A&A]

引用自 Peelingspud：

So the big question is will that Crucial ram be ok , will I notice the difference ?
Amazon.ca won't let me cancel the order even though it hasn't shipped so looks like I will either go through the hassle of returning the ram or use it.

Most RAM sticks in the market are using memory banks from Samsung, Hynix or Micron. The manufacturers do the rest, such as making printed circuit boards, heatsinks, etc.

[Peelingspud]

引用自 nullable：

It'll work. My position is going to be that having enough RAM, even if it's not optimal or a little bit slower is preferable to not having enough RAM.

You probably wouldn't be able to tell as a user, the results would only be visible in benchmarks. And again, if you added it to your existing memory it would run at the "slower" speeds. And I'm betting that it'll run just fine at 2666 CL15 or worst you run it all at a bit higher CL16 or something.

It's not the end of the world. It won't cripple your PC. In most cases it's a fairly marginal detail. And there's plenty of RAM benchmarky articles covering these topics that highlight the differences.

I'm a tad confused at your reply, I'm old so gimme a break Lol .
That Crucial ram I ordered is CL22, So what happens if I add it to my existing CL15 ram ?
I wasn't planning on adding it to my existing ram in case there was a conflict, and was just going to pull that ram and just use the new ram.

Btw, thanks for your replies.

[nullable]

引用自 Peelingspud：

引用自 nullable：

It'll work. My position is going to be that having enough RAM, even if it's not optimal or a little bit slower is preferable to not having enough RAM.

You probably wouldn't be able to tell as a user, the results would only be visible in benchmarks. And again, if you added it to your existing memory it would run at the "slower" speeds. And I'm betting that it'll run just fine at 2666 CL15 or worst you run it all at a bit higher CL16 or something.

It's not the end of the world. It won't cripple your PC. In most cases it's a fairly marginal detail. And there's plenty of RAM benchmarky articles covering these topics that highlight the differences.

I'm a tad confused at your reply, I'm old so gimme a break Lol .
That Crucial ram I ordered is CL22, So what happens if I add it to my existing CL15 ram ?

Generally when you add different speed RAM together all the RAM will be set to run at the slowest stick's speed. So mixing 2666 CL15 and 3200 CL22 would result in it trying to run at 2666 CL15. i suppose it's possible if the 3200mhz CL22 couldn't run at 2666 CL15 the system may slow everything down to 2400mhz CL-something, although I'm guessing a bit on that last detail. I've mixed plenty of RAM in my life, but maybe not to such extremes.

引用自 Peelingspud：

I wasn't planning on adding it to my existing ram in case there was a conflict, and was just going to pull that ram and just use the new ram.

Btw, thanks for your replies.

Well the great thing is you could try it with the existing RAM and see what the results are. It won't harm anything if you did discover issues, and you'd always have the option to remove the old RAM. Just depends on how curious you are I suppose.

[Peelingspud]

引用自 nullable：

Generally when you add different speed RAM together all the RAM will be set to run at the slowest stick's speed. So mixing 2666 CL15 and 3200 CL22 would result in it trying to run at 2666 CL15. i suppose it's possible if the 3200mhz CL22 couldn't run at 2666 CL15 the system may slow everything down to 2400mhz CL-something, although I'm guessing a bit on that last detail. I've mixed plenty of RAM in my life, but maybe not to such extremes.

I guess my biggest decision is will the new Crucial ram work okay just by itself without using the old memory, and will I notice any speed difference.

I'd like to get another Crucial stick to occupy all 4 slots to give me the maximum 64GB the board will take