[SOLVED] DDR5: Does CAS of faster RAM change at JADEC 4800

[pilotsh]

I can't seem to work this out or find an answer. Let's say one doesn't run XMP/EXPO (it voids warranty), and is happy to run at JADEC 4800 (ie does not engage XMP/EXPO in BIOS). Now let's compare three sets (each of two sticks) of DDR5 memory, say CL36 5200, CL36 5600 and CL40 5600.
Can anybody please explain to me (so I can learn why) which memory of the three sets would perform best or tie, if any, given overclocking (XMP/EXPO) is not selected - ie they run at JADEC 4800?

ie Will:
the 5200 set win, or
the two CL36 sets win (tie), or
all three sets perform the same, or
something else?

 

[kerberos_20]

they will run same with jedec clock/timings

 

[pilotsh]

they will run same with jedec clock/timings

So the CL36 kits will have no advantage over the CL40 kit? And if not, why not? (this is the part I don't understand.... because the CAS on two of them is "better", even when run at 4800, no?) ie don't the CL36 5200 and CL36 5600 kits run like "CL36 4800" and the CL40 5600 kit run like "CL40 4800"?

 

[kerberos_20]

So the CL36 kits will have no advantage over the CL40 kit? And if not, why not? (this is the part I don't understand.... because the CAS on two of them is "better", even when run at 4800, no?) ie don't the CL36 5200 and CL36 5600 kits run like "CL36 4800" and the CL40 5600 kit run like "CL40 4800"?

that is overclocked CAS, jedec CAS will be for all of them same, 40

 

[pilotsh]

that is overclocked CAS, jedec CAS will be for all of them same, 40

Ah, so even CAS is locked at JADEC, I just thought it was the speed at 4800. Excellent, thank you.

 

[kerberos_20]

Ah, so even CAS is locked at JADEC, I just thought it was the speed at 4800. Excellent, thank you.

ye its both clock and timings, jedec timings may have some small variations based on speed binning, but its nothing drastic

enabling XMP/EXPO raises voltage which allows higher clock and lower latencies
tbh rams have lifetime warranties...so that limiting factor is memory controller overclocking, you can enable XMP/EXPO and stay within CPU supported memory clock if youre worried that CPU (memory controller) will burn due to ram overclocking...nobody runs JEDEC...maybe on laptops, but thats because of lowering power
btw JEDEC is up to 6400MHz with plans to support up to 7200 in future

 

[kerberos_20]

here is example of XMP stick

this one shows XMP 6000 with CL36, but with jedec at 4800 CL can be 40 or 42
JEDED 6000 has CL 48 /54 which isnt shown here, but can be found in jedec papers and mainboard would set jedec timing once you rise clock without enabling XMP/EXPO

 

[pilotsh]

btw JEDEC is up to 6400MHz with plans to support up to 7200 in future

Ok, so I’ve done more research and now can see that. For example CL 40 40 40 5600 is also Jedec spec. So, running Jedec, requires activating XMP/EXPO, but AMD appears to say doing that will void warranty.
(from AMD website, my bolding)

1. Overclocking and/or undervolting AMD processors and memory, including without limitation, altering clock frequencies / multipliers or memory timing / voltage, to operate outside of AMD’s published specifications will void any applicable AMD product warranty, even when enabled via AMD hardware and/or software. This may also void warranties offered by the system manufacturer or retailer.

The key in this whole disclaimer is “operate outside of AMD’s published specifications”. So, where is AMD’s published specifications for RAM? (Is AMD referring to outside Jedec, like CL36 5600, for example?)

 

[pilotsh]

So, where is AMD’s published specifications for RAM?

I found my own answer, only 8 kits are approved so far!
https://www.amd.com/en/products/ryzen-compatible-memory-ryzen-7000-series-processor

 

[Kona45primo]

I would assume the warranty is in terms of the ability to run at XMP speed but necessarily to void the warranty on a CPU or motherboard.

Does anyone have any personal experience that any manufacturer will void a warranty because memory was used with XMP?

Case in point: https://www.pcworld.com/article/394...g-are-ok-even-if-they-void-your-warranty.html

2 lower CL could be considered +200mhz(ish) in a general sense. The benefit of lower CL is that certain CPU memory controllers may have a hard limit of how much frequency they can run, and or memory suppliers may have a limit on how fast they can increase ram MHZ/MT/S lower CL can help to increase performance beyond lower binned higher CL chips.

Lower CL chips may also be able to run faster secondary & tertiary timings which can further increase performance beyond just the single CL # listed. But that's enthusiast territory as it can take a lot of time to confirm what's the optimum stable frequency due to inevitable manufacturing variances in the CPU, Motherboard and Memory sticks.

 

[pilotsh]

If the RAM kit was on both the QVL list for the motherboard and CPU, warranty would hold (I find it extremely unlikely that the consumer affairs would rule against the consumer in that case, as it is an specified, approved, published and part). At least under Australian Consumer Law.