[SOLVED] DDR4: MHz vs CL

[eternalabys]

Hey, I'm looking to buy a kit of 16GB DDR4 3200MHz CL16 RAM or a kit of 16GB DDR4 3000MHz CL15 RAM, CPU will be a 2600X and because it likes lots of high speed RAM I was wondering which of the 2 kits would work best, so, should i get the kit with the tighter timings and OC the kit to 3200Mhz or should I just get the kit with looser timings but better clocks. (Mind you the kits are from the same brand: Crucial.)

If you are wondering what kits these are, they are the:

Crucial Ballistix Sport LT BLS2K8G4D30AESBK 3000MHz 16 GB CL15

and:

Crucial Ballistix Sport LT BLS2K8G4D32AESBK 16 GB CL16

(P.S The CL16 Kit costs a little bit cheaper which is also the reason apart curiosity for this thread.)

Thank you for your time.

 

[richiestang_78]

For gaming there really wont be much of a difference if any at all. I would still buy the lowest CL and Highest speed in your price range though if the difference is minimal

I would also suggest 3200mhz or higher for a Ryzen.

 

[alceryes]

I have had better luck getting faster (Mhz) RAM, upping the voltage a bit, and lowering the timings, than getting RAM with tighter timings and trying to get it to run at faster (Mhz) speeds.
YMMV, of course, but I would go with the 3200Mhz and slightly overvolt and lower the timings manually, if the choice were mine.

 

[eternalabys]

I've decided on using the 3200Mhz kit as it got even cheaper and after reading your comments.

Thanks for the input

 

[Karadjgne]

Ryzens do not like odd Cas numbers, so the 3000 C15 will most likely default to 3000 C16 instead.

 

[eternalabys]

What do you mean by "odd numbers"? Just in case the CAS latency of said CL15 RAM is 15-15-15-36. Would it still got to CL15 if I put on an XMP profile or manually OC them?

 

[TJ Hooker]

"Odd" as in not not even. E.g. 1, 3, 5, etc.

CL is stated in terms of clock cycles. 3200 MHz CL16 is actually equivalent to 3000 MHz CL15. Both have a real CAS latency of 10 ns. The 3200 MHz has higher bandwidth and the same latency, get that one.

 

[Karadjgne]

Ryzen uses ram speeds to set its Infinity Fabric. That's the speeds of communication between cores. Ram also has a Command Rate, you'll generally see it as 1T or more commonly 2T on the timings. Ryzens have a mode, Geardown (GDM) that allows the RAM to use a clock that’s one half the true DRAM frequency for the purposes of latching (storing a value) on the memory’s command or address buses. This conservative latching can potentially allow for higher clockspeeds, broader compatibility, and better stability. It does this by telling bios to ignore the set Command rate, and treats the ram as if it was 1T. This is a benefit to both the IF and the user for the most part. GDM is enabled by default in most bios. Part of GDM is that in order to do so, it sets ram in Even Cas numbers, 14 or 16 etc, since it cannot cut an odd number in half. With GDM enabled, that 15-15-15-36 would by default be changed to 16-15-15-36.

For OC'rs who will be overclocking past 2667MHz and attempting to force a 1T, it's better to disable GDM.

Issues getting XMP to work can sometimes be solved by disable GDM (if applicable) as that's a confusion trying to OC with bios ignoring set Command rate while being forced by XMP in bios to accept a 1T value.

 

[eternalabys]

Well, the CPU I'm getting is just a R5 2600. and that can only handle ram of 2933 MHz, So I thought getting lower MHz and lower CL would be better.

 

[TJ Hooker]

2933 MHz is what it's officially rated for; you can run faster, it's just technically an overclock at that point. Consider that there are currently no CPUs in existence officially rated for >3200 MHz, and yet there are tons of memory kits rates for faster speeds, up to like 5000 MHz.

You should be fine with 3200 MHz CL16. If you're concerned about compatibility then get a kit that's on your motherboard QVL list.

 

[DMAN999]

The maximim speed of your RAM will depend on your Motherboard and BIOS.
I have a 16 GB G.Skill TridentZ RGB CL 16 3200 kit on an Asus ROG Strix B450-F with a Ryzen 5 2600 that I was able to OC to 3400 MHZ with tighter timings.