# DDR4 CAS Latency



## RazrLeaf (Aug 22, 2014)

Any ideas how high/low CAS Latency on 2133 CL15 DDR4 will be?  I was looking at a some information on Wikipedia, and was wondering how DDR4 would compare.


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## Frick (Aug 22, 2014)

CL15 = CAS latency 15.

As always, it will not be worth it at first (I assume, cadaveca will correct me if I'm wrong (I see you!)) but eventually it will.


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## cadaveca (Aug 22, 2014)

Frick said:


> CL15 = CAS latency 15.
> 
> As always, it will not be worth it at first (I assume, cadaveca will correct me if I'm wrong (I see you!)) but eventually it will.


All things in due time...


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## EarthDog (Aug 22, 2014)

Due time... That is for those under NDA... oh wait... so am I... 

Being more serious, one of the big take aways from DDR4 is their low voltage. You will see (check out the Gskill press release) 1.2v and CL15 at 2133 and CL16 1.35v at obnoxious 3200MHz speeds versus the 1.65v+ it takes to get there now (granted with lower latency in a lot of cases). 

Bandwidth isn't an issue anyway so, unless they offer something more, it, like quad channel in most cases, is pretty MEH.


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## RazrLeaf (Aug 22, 2014)

Well, I asked my question in a foolish way.
Will the latency in ns be the same as they are for respective DDR3 modules given the same clock speed and CL?


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## LaytonJnr (Aug 22, 2014)

RazrLeaf said:


> Well, I asked my question in a foolish way.
> Will the latency in ns be the same as they are for respective DDR3 modules given the same clock speed and CL?



What you are referring to there is known as RAM 'access time', or more casually as RAM 'speed' or 'performance', which is basically the time it takes in nanoseconds for the RAM to locate a single piece of information and make it available to the processor (a very rough definition). Latency is a reference to CAS timings, which refers to the delay between the memory controller telling the RAM to 'find' the information, and the information being made available.

The general way to work out RAM access time is: ( CL / Frequency ) * 1000.

So, for 2133MHz CL15 DDR4 memory, ( 15 / 2133 ) * 1000 = 7.03ns

And for 1600MHz CL9 DDR3 memory, ( 9 / 1600 ) * 1000 = 5.63ns

So actually, DDR3 memory is faster in terms of access time between these two examples (as AFAIK 2133MHz is meant to be the standard DDR4 RAM frequency). As many people have already said, DDR4 RAM probably will eventually have better access time than DDR3 in due time.

Layton


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## cadaveca (Aug 22, 2014)

LaytonJnr said:


> What you are referring to there is known as RAM 'access time', or more casually as RAM 'speed' or 'performance', which is basically the time it takes in nanoseconds for the RAM to locate a single piece of information and make it available to the processor (a very rough definition). Latency is a reference to CAS timings, which refers to the delay between the memory controller telling the RAM to 'find' the information, and the information being made available.
> 
> The general way to work out RAM access time is: ( CL / Frequency ) * 1000.
> 
> ...


That's a good way to look at it, although, truly, yyou'd be better off comparing 1066 MHz or 1333 MHz DDR3 vs. 2133 DDR4, since these are "base speeds" each technology will have launched at. Comparing DDR3 1600 would be comparable to a higher DDR4 speed than 2133 MHz... perhaps DDR4-2666 or DDR4-3000 might be the more accurate compare.

If you are simply comparing what's available now, it would be more prudent, IMHO to maybe compare DDR3-2400 to DDR4-3000 or DDR4-3200. Or you could go by price... I'm not sure where the truly accurate comparison is at this point.

And no, EarthDog, I do not have an NDA on DDR4. However, I do feel that all info must be provided in proper context, and that context does have some limitations for me at this time.


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## RazrLeaf (Aug 22, 2014)

I just wanted to know of they used the same units/measurements when reporting specs.  That was most helpful (and educational). Thanks.


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## EarthDog (Aug 22, 2014)

Yes.

They didn't switch the barometer(how they measure) in the middle of the game... That is like saying they measure an automobile's horsepower by using baseballs, LOL!


Dave, I meant the platform, not DDR4 specifically.


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## cadaveca (Aug 22, 2014)

EarthDog said:


> Yes.
> 
> They didn't switch the barometer(how they measure) in the middle of the game... That is like saying they measure an automobile's horsepower by using baseballs, LOL!
> 
> ...


NO Intel NDA either...


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## LaytonJnr (Aug 22, 2014)

cadaveca said:


> That's a good way to look at it, although, truly, yyou'd be better off comparing 1066 MHz or 1333 MHz DDR3 vs. 2133 DDR4, since these are "base speeds" each technology will have launched at. Comparing DDR3 1600 would be comparable to a higher DDR4 speed than 2133 MHz... perhaps DDR4-2666 or DDR4-3000 might be the more accurate compare.
> 
> If you are simply comparing what's available now, it would be more prudent, IMHO to maybe compare DDR3-2400 to DDR4-3000 or DDR4-3200. Or you could go by price... I'm not sure where the truly accurate comparison is at this point.
> 
> And no, EarthDog, I do not have an NDA on DDR4. However, I do feel that all info must be provided in proper context, and that context does have some limitations for me at this time.



I did a little bit of digging, and the base level for DDR3 on launch was 1066MHz CL7 and 1333MHz CL8, and the base level for DDR4 is claimed to be to the tune of 2133MHz CL13. Time for some more math.

So for DDR3, the RAM access times are 6.57ns and 6.00ns respectively. And for DDR4, the RAM access time is 6.09ns. Hence, the entry level 'access times' of both technologies is comparably similar at the base level at launch.

Layton


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## EarthDog (Aug 22, 2014)

cadaveca said:


> NO Intel NDA either...


I guess TPU is missing the boat... or you are being an ass to me... Id bet on the later.


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## cadaveca (Aug 22, 2014)

EarthDog said:


> I guess TPU is missing the boat... or you are being an ass to me... Id bet on the later.


Nah, I will have my launch-day coverage. I just do not have NDAs for most of what the platform offers. I'm only not reporting anything worthwhile early out of respect for the companies involved.

I just manage to do this for every launch, get what I need without having to sign NDAs, and without having to use ES parts.  Any site should be able to do the same, IMHO. If other sites are signing NDAs, and are restricted to ES parts for launch day reviews...it's THEM, and their readers...that are missing out. 

Or perhaps I have a better relationship with Intel. Who knows. ROFL.


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## EarthDog (Aug 22, 2014)

Looking forward to your 'launch day, no NDA, no ES' coverage!


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## ZenZimZaliben (Aug 22, 2014)

Every new generation of ram does this. The difference in CAS rating is due adjustments in higher/lower bandwidth and manufacturing tolerances. I am totally excited for Haswell-E, X99, DDR4! Been waiting to upgrade and this will be it.

DDR: CAS 2, 3 - Command Rate: 166, 200
DDR2: CAS  4, 6 - Command Rate: 333, 400, 533
DDR3: CAS 5, 11 - Command Rate: 533, 666, 687, 800, 1066, 1200
DDR4: CAS 10, 22 - Command Rate: 1600, 1866, 2133, 2400, 2666, 3200, ???


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## Hilux SSRG (Aug 22, 2014)

LaytonJnr said:


> What you are referring to there is known as RAM 'access time', or more casually as RAM 'speed' or 'performance', which is basically the time it takes in nanoseconds for the RAM to locate a single piece of information and make it available to the processor (a very rough definition). Latency is a reference to CAS timings, which refers to the delay between the memory controller telling the RAM to 'find' the information, and the information being made available.
> 
> The general way to work out RAM access time is: ( CL / Frequency ) * 1000.
> 
> ...



That's an easy way to do quick comparisons, thanks for sharing.


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## X71200 (Aug 22, 2014)

Unless you're comparing shit DDR4 to good DDR3 expect DDR4 to be faster, not slower. It's the bandwidth that matters the most for performance and not CAS latency, as long as speeds and timings go in line. There are already high end DDR4 RAM such as Dominator Platinums made with extremely high frequencies. Here is an example of comparison, as you can see from the pic TridentX 2933 did better than it's 2600 version even though it has higher CAS latency.


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## LAN_deRf_HA (Aug 22, 2014)

That pic isn't really going to sell anyone on speed before cas, in fact the review it comes from would seem to show the opposite. Especially if you want to do well benchmarking.


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## cadaveca (Aug 22, 2014)

LAN_deRf_HA said:


> That pic isn't really going to sell anyone on speed before cas, in fact the review it comes from would seem to show the opposite. Especially if you want to do well benchmarking.



Way to hand-pick the benchmark that shows that single-sided sticks are not as good as dual-sided sticks in all apps to prove an unrelated point.


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## X71200 (Aug 22, 2014)

LAN_deRf_HA said:


> That pic isn't really going to sell anyone on speed before cas, in fact the review it comes from would seem to show the opposite. Especially if you want to do well benchmarking.



How come slower memory comes up with higher R/W results?

And yes, speed does become in front of CAS latency. If it didn't then DDR 400 CL2 would have performed better than DDR2 800 CL4 and DDR2 800 CL4 would have performed worse than DDR3 1600 CL8.



cadaveca said:


> Way to hand-pick the benchmark that shows that single-sided sticks are not as good as dual-sided sticks in all apps to prove an unrelated point.



Care to elaborate?


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## cadaveca (Aug 22, 2014)

X71200 said:


> How come slower memory comes up with higher R/W results? Care to elaborate?




I think you already did. Once you've played with a lot of DDR3, you learn to recognize these things for what they are.


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## LAN_deRf_HA (Aug 23, 2014)

cadaveca said:


> Way to hand-pick the benchmark that shows that single-sided sticks are not as good as dual-sided sticks in all apps to prove an unrelated point.



You're reading too much into it. He made a non-point and I threw it back at him, but since you bring it up that's not really a defense of the crappiness of high speed kits either. Unless you're saying they now have dual sided 2933 and higher kits? I haven't seen any yet.



X71200 said:


> And yes, speed does become in front of CAS latency. If it didn't then DDR 400 CL2 would have performed better than DDR2 800 CL4 and DDR2 800 CL4 would have performed worse than DDR3 1600 CL8.



We're speaking in more practical terms than your example. I'd take a 2400 c9 kit over any of the 2933 kits I've seen, and I'd save a ton of money and have the same or better performance for it. Those bandwidth or bust situations are hard to find.


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## cadaveca (Aug 23, 2014)

LAN_deRf_HA said:


> You're reading too much into it. He made a non-point and I threw it back at him, but since you bring it up that's not really a defense of the crappiness of high speed kits either. Unless you're saying they now have dual sided 2933 and higher kits? I haven't seen any yet.




You don't pay attention to ram like I do. Not that you'd have any reason too... But I'm a ram geek.

so here you go:

http://www.newegg.com/Product/Produ...p=&AID=10446076&PID=6146846&SID=182eb60nw67z2


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## X71200 (Aug 23, 2014)

cadaveca said:


> I think you already did. Once you've played with a lot of DDR3, you learn to recognize these things for what they are.



That's a non-answer.



LAN_deRf_HA said:


> You're reading too much into it. He made a non-point and I threw it back at him, but since you bring it up that's not really a defense of the crappiness of high speed kits either. Unless you're saying they now have dual sided 2933 and higher kits? I haven't seen any yet.
> 
> We're speaking in more practical terms than your example. I'd take a 2400 c9 kit over any of the 2933 kits I've seen, and I'd save a ton of money and have the same or better performance for it. Those bandwidth or bust situations are hard to find.



Non-point as in what? The OP is obviously wondering whether DDR4 will perform better or not in the end. There's no "crappiness" of high speed kits.

A 2933 kit WILL perform better than a 2400 kit regardless of it's higher timings. Period.


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## JoshuaAJones (Sep 6, 2014)

LaytonJnr said:


> What you are referring to there is known as RAM 'access time', or more casually as RAM 'speed' or 'performance', which is basically the time it takes in nanoseconds for the RAM to locate a single piece of information and make it available to the processor (a very rough definition). Latency is a reference to CAS timings, which refers to the delay between the memory controller telling the RAM to 'find' the information, and the information being made available.
> 
> The general way to work out RAM access time is: ( CL / Frequency ) * 1000.
> 
> ...


Your math is accurate for the old SDRAM but for all DDR SDRAM you must multiply by 2000.
Therefore, in your examples:
2133MHz CL15 DDR4 memory, ( 15 / 2133 ) * 2000 = 14.06ns
1600MHz CL9 DDR3 memory, ( 9 / 1600 ) * 2000 = 11.25ns



X71200 said:


> That's a non-answer.
> 
> 
> 
> ...


Actually, 2400-CL9 is faster than 2933-CL12 (the only CL I can find)...
DDR3 2400-CL9 = 7.50ns (~$270US for a 16G Kit)
DDR3 2933-CL12 = 8.18ns (~$700US for a 16G Kit)
DDR4 3000-CL15 = 10.00ns (~$390US for a 16G Kit)

As for now, the only reason to go to DDR4 is for the low power draw (1.2V vs 1.65V).
Give it some time though and we'll see DDR4 prices drop and speeds soar.
Eventually, they'll get up to DDR4 4200-CL15 (7.14ns) using only 1.35V.


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## buildzoid (Sep 7, 2014)

X71200 said:


> That's a non-answer.
> 
> 
> 
> ...


 sorry but no due to how 2933+mhz ICs are designed they are hopeless when it comes to real world performance if this wasn't the case pro overclockers would use them for benchmarking not just ram frequency suicide runs. Dave even reviewed a 2933 kit and it got destroyed in everthing by a 2400 kit. Timings matter and frequency does to but at somepoint the increase in time spent finding and accessing data negates the speed at which the data travels. This is typically the case with ddr3 ram going over 2800mhz.
As for op's question just look at some haswell-e superPi scores compared to haswell superPi scores and you can see that ddr4 2666 14-10-10-28 is pretty much on par with ddr3 2133 8-10-8 and ddr3 2800 9-10-10.


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## EarthDog (Sep 10, 2014)

Make sure you are looking at 32M runs to see the effect on ram. While 1M does respond to faster memory speeds, it is more or less handled all in cache. So 32M will give you a better idea.


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## Mike Rollins (Jul 5, 2015)

JoshuaAJones said:


> Your math is accurate for the old SDRAM but for all DDR SDRAM you must multiply by 2000.
> Therefore, in your examples:
> 2133MHz CL15 DDR4 memory, ( 15 / 2133 ) * 2000 = 14.06ns
> 1600MHz CL9 DDR3 memory, ( 9 / 1600 ) * 2000 = 11.25ns
> ...



I know this post is dated, but I ran across it since I'm researching some new memory to purchase.

The example you used here to calculate the speed, which you said is more accurate and the formula used previously, towards the beginning of the post (using the divisor as the stated speed cut in half and then multiplying by 1000), which you said was inaccurate because it's for old SDRAM. Did you even stop to think more into this formula you said was correct while bashing the other (using the stated memory speed as the divisor and then multiplying it by 2000 instead of 1000)? If you stopped and thought about it for a second, when you increase the divisor by 2x and then increase the multiplier from 1000 to 2000, it would be the exact same formula. That would be like saying instead of the answer being (15/1500)*1000=10ns vs. (15/3000)*2000=10ns.  Just my $0.02.


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## Lagittaja (Dec 28, 2015)

Mike Rollins said:


> I know this post is dated, but I ran across it since I'm researching some new memory to purchase.
> 
> The example you used here to calculate the speed, which you said is more accurate and the formula used previously, towards the beginning of the post (using the divisor as the stated speed cut in half and then multiplying by 1000), which you said was inaccurate because it's for old SDRAM. Did you even stop to think more into this formula you said was correct while bashing the other (using the stated memory speed as the divisor and then multiplying it by 2000 instead of 1000)? If you stopped and thought about it for a second, when you increase the divisor by 2x and then increase the multiplier from 1000 to 2000, it would be the exact same formula. That would be like saying instead of the answer being (15/1500)*1000=10ns vs. (15/3000)*2000=10ns.  Just my $0.02.



I know this post is dated, but I ran across it since I'm researching DDR4...

Actually Laytonjnr's calculations were incorrect and JoshuaAJones's was correct..
Laytonjnr calculated using
(CL / Data rate) * 1000
Which is correct for _SDR_ SDRAM but incorrect for _DDR_ SDRAM.

What we're calculating here (for DDR) can be achieved using for example:
a)
(CL / (Data rate / 2)) * 1000
b)
(CL / IO Bus Clock) * 1000´
c)
(CL / Data rate) * 2000
or whatever variation you can think of.

JoshuaAJones calculated using c which gives the same results as a and b.

(15/(2133/2)*1000 = 14,06ns
(15/1066,5)*1000 = 14,06ns
(15/2133)*2000 = 14,06ns

(15/2133)*1000 = 7,03ns


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## sneekypeet (Dec 28, 2015)

In case you like pictures of how it all correlates... http://www.crucial.com/usa/en/memory-performance-speed-latency


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## Aquinus (Dec 29, 2015)

Just for clarity, there are cases where things big sequential reads offer improved performance because some latencies are omitted because of the kind of change in address that occurred. For example, it takes fewer cycles to go from column to column as opposed to row to row. None of this really matters in the end though because most workloads can buffer memory read/write requests in cache. The biggest win here is *writeback* cache. Where active memory isn't written to immediately but (in terms of modern Intel CPUs,) will get written to L3. The CPU will acknolege a successful memory operation once it has been written to L3 but, in reality it's being queued up to be written to main memory. Meanwhile, between now and then, that data is accessible by all of the cores and attached cores (via QPI on MP systems,) without touching system memory. This caching concept starts to degrade when writing a lot of data to system memory, faster than system memory can be written to but, so long as the IMC has overhead is within that capabilities of the last level of cache accessible to the cores, memory bandwidth and latency means very little and it is in fact the speed of the SRAM cache in the CPU than can have a greater impact on performance.

All in all, memory has a point of diminishing returns, just as cache does because in the end, you can only feed a core so much data and you can only shove so many cores on a die and software can only be made to be so parallel. It's the nature of computers; the bottleneck problem.


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## Mike Rollins (Dec 29, 2015)

Wow! This thread continues to revive itself. Well, since I posted here almost a year ago, I sold my Corsair Vengeance LPX 2800 CL16 DDR4 memory and bought Kingston HyperX 2400 CL12 DDR4 memory, and I must say, it worked out better than the Corsair. But, I think there may have been some incompatibility issues with the Corsair LPX memory and the Asus X99 Deluxe MB, which I still have but it's on the shelf while I work on a new build. 

With the X99 chipset, anything over 2666Mhz you had to increase the BCLK to 125 from 100, actually 127.3 BCLK was the sweet spot. Running a higher BCLK presented other problems, so I downgraded my speed and got a faster latency. Since my rig is torn apart and has been since Sept, I can't comment on how my HyperX memory runs on my new Rampage V Extreme. Who knows, maybe in another year, someone else will post on this thread and say, "What are you talking about? RAM? We're all using 3D Xpoint memory."


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## dr_lucas (Mar 29, 2016)

LaytonJnr said:


> What you are referring to there is known as RAM 'access time', or more casually as RAM 'speed' or 'performance', which is basically the time it takes in nanoseconds for the RAM to locate a single piece of information and make it available to the processor (a very rough definition). Latency is a reference to CAS timings, which refers to the delay between the memory controller telling the RAM to 'find' the information, and the information being made available.
> 
> The general way to work out RAM access time is: ( CL / Frequency ) * 1000.
> 
> ...



Crucial has an interesting article that doesn't really match this calculation:
http://www.crucial.com/usa/en/memory-performance-speed-latency

I am a bit confused...can anyone explain which one is correct?


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## Lagittaja (Mar 30, 2016)

dr_lucas said:


> Crucial has an interesting article that doesn't really match this calculation:
> http://www.crucial.com/usa/en/memory-performance-speed-latency
> 
> I am a bit confused...can anyone explain which one is correct?



Could you even bother to try and read the whole thread first?

And just in case you're lazy, you'll find your answer a few posts above of yours



Lagittaja said:


> I know this post is dated, but I ran across it since I'm researching DDR4...
> 
> Actually Laytonjnr's calculations were incorrect and JoshuaAJones's was correct..
> Laytonjnr calculated using
> ...


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