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.

[nullable]

Първоначално публикувано от Peelingspud:

Първоначално публикувано от 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 don't think you're notice a difference in normal use. The 3200mhz CL22 RAM is effectively slower than your 2666 CL15. But slow in the scales we're talking about, a couple of nano seconds. I'd wager I could replace your RAM with random sticks every day and you wouldn't notice most of the time.

Although you could always try it out and see for yourself. Although if you're really concerned I'd opt for higher performing DDR4 CL14-16 3200mhz RAM. Even if the differences are generally small, as an enthusiast I can't help but opt for something a bit better given a choice.

If you really want guaranteed performance improvements no matter how small, return the 3200mhz CL22 and get 3200mhz with a lower CL.

[Peelingspud]

Първоначално публикувано от nullable:

Първоначално публикувано от Peelingspud:

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 don't think you're notice a difference in normal use. The 3200mhz CL22 RAM is effectively slower than your 2666 CL15. But slow in the scales we're talking about, a couple of nano seconds. I'd wager I could replace your RAM with random sticks every day and you wouldn't notice most of the time.

Although you could always try it out and see for yourself. Although if you're really concerned I'd opt for higher performing DDR4 CL14-16 3200mhz RAM. Even if the differences are generally small, as an enthusiast I can't help but opt for something a bit better given a choice.

If you really want guaranteed performance improvements no matter how small, return the 3200mhz CL22 and get 3200mhz with a lower CL.

Okay, thank you for all your relies, very useful info, much appreciated !

[Peelingspud]

Първоначално публикувано от nullable:

If you really want guaranteed performance improvements no matter how small, return the 3200mhz CL22 and get 3200mhz with a lower CL.

Well I've been looking for 2 hrs for compatible ram and can't find anything for my system so I guess I will try the Crucial ram when it arrives and see how it works with my games.

[Bad 💀 Motha]

Go with Corsair or GSkill DDR4 3200 at CAS 15 or 16

2x 16GB

Don't mix with the old RAM.

Sell the old RAM or put into another machine.

2x 8gb DDR4 2666 would be better suited in an older AMD Ryzen system or perhaps an older locked Intel i3/i5/i7 system such as 8th, 9th or 10th gen

[WarBucks]

Motherboard manufacturers usually have a list of "compatible" ram they tested when they released the board. But they never go back and test sticks that come out later.

Thats the reason say an older laptop with 2 slots for ddr4 might say "max 32GB". when in fact its good into 64GB.

When the laptop came out 32GB sticks werent available yet for the OEM to test with.

im sure its the same for your motherboard

edit: thats not to say all ram will work to its full potential. just that anything new should be functionally backward compatible

[_I_]

mobo qvl list is useless
the mobo mfg does not have the time or all the dimms to test every possible combo

[Peelingspud]

UPDATE: I finally ended up getting this ram, Kingston Fury Beast-3200MHz-Memory-KF432C16BB1-16

It says it's cl16 but when I ran cpu-z it shows as cl17, runs at 2400mhz but that's to be expected being as an i7-770K will only run at that speed without overclocking.
When I tried enabling xmp in the BIOS ( it shows 2 profiles ) the computer wouldn't boot, have no idea why.
I think I could overclock the memory to up the speed but not entirely comfortable doing that as I have never done that.
No doubt someone will say I could have done better and cheaper than the $60CAD I paid for 4 16GB modules (total of $240 ) but I knew this ram would work after checking with my local supplier that I bought the computer parts from originally.
Thanks for all the useful info you guys posted.

[_I_]

at lower freq it can run lower timings
3200/16 = 200
at 2400 it should be able to do closer to 12

it will easily run at the speed of your orig ram

[nullable]

Well yes the default speed without XMP enabled would be lower than the marketed speed on the RAM. You get that speed through XMP. It's interesting that it wouldn't boot with XMP enabled. Do you have options for different versions of XMP?

Alternatively, if you never updated the BIOS on your motherboard there's a chance (unless you're already on the latest) that a BIOS update may address compatibility issues, stability issues (XMP) or bugs. It might be worth a peek.

Upside is Intel systems are less sensitive to RAM speed so you're not really crippled running at lower speeds. But squeezing a smidge more performance out of the system is better than a poke in the eye if you can manage it.

[_I_]

if you re mixing ram you cannot use xmp, unless all dimms have compatible profiles

[Peelingspud]

Първоначално публикувано от _I_:

if you re mixing ram you cannot use xmp, unless all dimms have compatible profiles

I got 4 dimms of the same ram like I posted.

[Peelingspud]

Първоначално публикувано от nullable:

Well yes the default speed without XMP enabled would be lower than the marketed speed on the RAM. You get that speed through XMP. It's interesting that it wouldn't boot with XMP enabled. Do you have options for different versions of XMP?

Have no idea and don't know what version I have, I'll check. I do know that my old ram (2x8GB sticks ) showed as running at 2666 which I thought was weird as it wasn't overclocked and XMP was disabled, but the new ram shows 2400MHz

Първоначално публикувано от nullable:

Alternatively, if you never updated the BIOS on your motherboard there's a chance (unless you're already on the latest) that a BIOS update may address compatibility issues, stability issues (XMP) or bugs. It might be worth a peek.

I believe I updated the BIOS when I first got the machine around 2016-17 but I will check that.

Първоначално публикувано от nullable:

Upside is Intel systems are less sensitive to RAM speed so you're not really crippled running at lower speeds. But squeezing a smidge more performance out of the system is better than a poke in the eye if you can manage it.

I'll see how the new ram goes once I've checked the programs I use.
The main reason I upgraded is that I have a recording studio and more ram is always better for my DAW for that purpose, and for stability it's always recommended to not overclock.

Thanks for the useful info nullable, much appreciated !

[Peelingspud]

Първоначално публикувано от _I_:

at lower freq it can run lower timings
3200/16 = 200
at 2400 it should be able to do closer to 12

Sorry but I don't understand what you are saying here.

[r.linder]

Първоначално публикувано от Peelingspud:

Първоначално публикувано от _I_:

at lower freq it can run lower timings
3200/16 = 200
at 2400 it should be able to do closer to 12

Sorry but I don't understand what you are saying here.

With higher DRAM frequency, it's easier for the RAM to run lower timings.

CAS Latency itself doesn't matter as a stat, the subtimings do more than the primary timings.

https://www.youtube.com/watch?v=pgb8N23tsfA

[nullable]

There is an argument that if the first number is bad, the sub timings aren't going to be amazing either. And sure the sub timings for something that's CL16 could be different between two different models of RAM and one could be better than the other. So I would look at the sub timings too, personally, but generally I'd also wager the sub timings on something like 3200mhz DDR4 CL16 are going to be better than the sub timings on 3200mhz DDR4 CL22.

Overall I'm not that fussed about it, CL is just another data point long with speed, that can tell you a bit about the expected performance. Sometimes you might care more for your finely tuned custom built machine, so the details are important. And you might not care so much for your random aging prebuilt, because you don't care about the RAM in it now, and RAM is gonna be good enough.

There's a spectrum of concern I'd say.