Is latency going to be a problem on DDR5 modules?

[g67575]

I worked out the total latency on a fairly typical DDR5 4800mhz Crucial RAM module, with a CAS latency of 40. It's worked out as follows:
40 / 2400 (rated Mhz divided by 2), x 1000 = 16.6ns.

This is a fair bit more than my DDR4000 CL 19 kit, with a total latency of 9.5ns.

What this tells me me, is that a DDR5 4800mhz module would need a CAS Latency of 22, for a reduced latency of 9.16ns.

Alternatively, a DDR5 8000mhz module would need a CAS latency of 40 to achieve a slightly higher latency of 10.0 ns.

Are lower CAS latency modules a remote possibility in the next couple of years?

 

[g67575]

Everyone knows you should wait 3-5 years before buying into a new generation

That would count you out of Zen 4 then, which is very likely DDR5 only.

 

[g67575]

6600 CL36 already confirmed for this year

That's interesting, so total latency of 10.9ns. Not too far off most DDR4 modules.

The problem is, you will pay a lot for the luxury of higher bandwidth modules and OK latency.

It looks like most of the catchup will be in increasing the total bandwidth, assuming they don't need to raise the CAS latency above 36. In terms of overall performance, that would also yield the best results.

Link here:
https://www.techpowerup.com/288082/...fastest-ddr5-6600-cl36-trident-z5-memory-kits

 

[g67575]

So, 7600mhz DDR5, CL 36 would have a total latency of 9.4ns, so this is roughly the spec they need to reach to overtake the performance of most DDR4 modules, in my opinion.

Also, there's the memory controller gears to worry about on Alder Lake too.

Geil is apparently working on DDR5-6400 modules with a CL of 32, which equates to 10ns. Link here:
http://www.geil.com.tw/news/?id=41

 

[g67575]

@Grim5 - A bit obvious that most DDR5 modules have higher bandwidth, given the higher frequencies. Do you mean it increases the bandwidth more than you'd expect with even higher frequency DDR4?

 

[g67575]

I think gamers will probably want improved bandwidth and similar latency to DDR4, but it won't necessarily be an affordable option for most.

The Geil DDR5-6400 CL32 kit looks decent, if it does see the light of day.

I'm trying to pick out some decent RAM for my dad, he seems to think DDR5 will just be better than the previous tech.

 

[g67575]

(38 / 2600) divided by 1000 = 14.6 nanoseconds of latency.

Eventually I think the high frequency RAM will offer low latency, but it will take a while.

 

[g67575]

And why is this thread in the CPU section and not in the Memory section?

I don't know, its pure chaos and insanity isn't it?

 

[g67575]

I think overclocking will only be worth it if you can increase the frequency, without changing the base CAS Latency.