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?

 

[Psycho Sonny]

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

 

[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.

 

[PiKe]

Isn't it less of a problem because there are 2*32bit vs a single 64bit bus on DDR4?

 

[Psycho Sonny]

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

Don't really care. Cost of ddr5 will come down from £300 to £150 at some point.

CPUs, motherboards, etc will mature too over time and so will the new gen tech and so will prices.

I made sure I had top spec now so I don't need to buy overpriced next gen stuff.

I remember buying ddr4 when it came out paid £200 for some ram and then a few years later I'm paying £75 for much better ram.

Pointless buying into new tech early

 

[Perfect_Chaos]

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

5 years would be way too long, you'd be buying right before DDR6.

6600 CL36 already confirmed for this year, 6-12 months should see a quick increase again in timings/speed.

 

[Psycho Sonny]

5 years would be way too long, you'd be buying right before DDR6.

6600 CL36 already confirmed for this year, 6-12 months should see a quick increase again in timings/speed.

I said 3-5 not 5.

I have a 5600x and very good ddr4 so I don't see any upgrade being worthwhile for me for 5 years.

However those on older systems will want to upgrade on around 3 years once it's matured and price is half what it is now.

 

[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

 

[Grim5]

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

Is latency the only things that matter for games? Then drr3 should be better than DDR4 for games

If bandwidth is important then DDR5 is already beating DDR4 easily in bandwidth throughout - bandwidth test results in Aida64 show throughout being 90gb/s on current kits

 

[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?

 

[Poneros]

Have to see benchmarks first, and how much tuning can be done with DDR5.

 

[Grim5]

@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?

No I just want to know how you can estimate gaming performance from paper Ddr5 specs

your analysis seemed to place high importance on latency, but then DDr3 should be the best since its latency is even better

 

[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.

 

[jigger]

Probably. You’d have to look at Ring bus and Mesh performance compared to latency/bandwidth. We don’t know the NUMA arrangement on Intel’s system and that will be another variable.

My hunch is yes and no.

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.

4x sticks of single rank Samsung B-Die at 1.6v on a super skookum X570S FTW.
ASUS ROG X570 Crosshair VIII Extreme with a Ryzen 5800X for maximum performance. Glorious motherboard master race.

A 5700G is probably the ideal chip for a super low latency platform. I’ve got one that will run the IF at 2200, so that would allow for a potential pairing with 4400mhz cas 14~ on a single die CPU.

Drop a Ryzen 5700G in a ASUS ROG X570 Crosshair VIII Extreme or EVGA X 570 Dark motherboard with some 8 pack binned B-Die and a RX 6900XTXH and it might make gamers heads explode.

 

[Aretak]

Is latency the only things that matter for games? Then drr3 should be better than DDR4 for games

If bandwidth is important then DDR5 is already beating DDR4 easily in bandwidth throughout - bandwidth test results in Aida64 show throughout being 90gb/s on current kits

Both matter. You can easily see from testing of current DDR4 that both higher speeds and tightened timings help gaming performance. Some games care a lot more about system memory than others though, and you'll see by far the biggest benefit when you're CPU-bound.

https://kingfaris.co.uk/blog/intel-ram-oc-impact

There's no point pumping a ton of extra bandwidth if it means your timings go to crap. The XMP timings of many really fast DDR4 kits are awful and will provide lower real world performance than a slower, but highly tuned kit (but of course a faster kit that's also tuned will be even better). Buildzoid did a video about this just recently:

Early DDR5 likely won't be any upgrade at all over a highly-tuned kit of DDR4. It may even be worse. Over time it will pull ahead as speeds get faster, timings get tighter and people learn how to tune the things that XMP doesn't cover. Comparing the very first, low-end DDR5 to the best DDR4 on the market is pointless. Early DDR4 was absolute garbage. It took a couple of years for quality ICs like Samsung B-Die and Micron Rev. E to arrive, be recognised and really show the potential of the technology.

 

[alexkyriak]

So for someone who hasn’t really ever considered RAM in detail ever before (ie, me!) can anyone explain how ddr5 works?

It’s got double bandwidth, and high speed, but the timings are slower. So how does one figure out how good it’ll be? take this RAM as an example:

https://www.overclockers.co.uk/cors...UfpHdSDhljA-1635586734-0-gqNtZGzNAtCjcnBszQ79

GDDR5 5200mhz 38 38 38 84

I realise probably need to wait for tests and reviews, but I’m not sure I fully understand the timings/speed/bandwidth relationship.

Is it basically the case that as DDR5 matures those timings will drop?

 

[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.

 

[jigger]

It’s not only the RAM that needs to be considered. It’s how everything is wired to the chip. Or in this case chips, and how those chips are wired to each other.

If core 0 on ring 1 needs access memory and the part of the chip that the memory is liked to, is on the mesh side then the data has to hop around and out of its ring, into the mesh (if direct access if available) around the mesh and then to the memory. So maybe 8 hops before the memory can do its thing.

All we know so far is the big cores are a ring bus and arranged in clusters of 4, and the Atom cores are a mesh and arranged in clusters of 8. The glue or IMO glues that link everything are unknown. Without knowing how those 16 cores packaged it’s hard to understand what effect memory performance will have on the overall processing speed.

 

[Joxeon]

Can just get a standard kit and overclock it yourself, if you watch a lot of buildzoids vids he said that even the standard ddr4 2400mhz kits will hit 4000+ once you put enough voltage through it and it'll probably be the same for DDR5.

The standard kits operate at 1.1v and the latest 6400 kits use 1.25 so if you stick 1.45 through the ram I'd imagine 8000+ would be very doable even on the base kits.