Relationship Between Latency and Frequency

[Raytsou]

Why does it seem that the higher the frequency of the ram, the higher the latency? Isn't latency the delay between the cpu and the ram? Wouldn't that mean that higher clock speed should lower frequency? This is something I never understood despite considering myself a "techie". Every I look, people just say, "get DDR3-1600 CAS 9, it's good enough."

[Guest]

Ideally you want lower cas and high speed RAM

Its essentially how fast your memory interacts with your CPU

*someone correct me if I'm wrong*

It really only matters if your an Overclocker like me, who try to get 

EVERY
LAST
MARK

out of cinebench 

[vanished]

I'm no expert on memory, but I think it's simply only able to do so many things per second, and so to maintain that limit, you have to trade frequency with latency.  Improving both would push it too far.  (sorry experts if that explanation is painful )

[Raytsou]

Ideally you want lower cas and high speed RAM

Its essentially how fast your memory interacts with your CPU

*someone correct me if I'm wrong*

It really only matters if your an Overclocker like me, who try to get 

EVERY

LAST

MARK

out of cinebench 

I understand that, but I'm asking why does higher frequency ram have higher latency compared to lower frequency ram?

[Raytsou]

I'm no expert on memory, but I think it's simply only able to do so many things per second, and so to maintain that limit, you have to trade frequency with latency.  Improving both would push it too far.  (sorry experts if that explanation is painful )

I don't think that's the case, because if it is, then what is the point of having faster memory?

[Enderman]

I understand that, but I'm asking why does higher speed ram have higher latency compared to lower speed ram?

latency is how long it takes to access the ram

the frequency is how fast it can take in or out data

 

so lower latency is better for lots of small files since it gets to them faster

but higher frequency is better for few large files

 

this is why some programs work better with lower latency while others with higher frequency

higher frequency also heats up the ram more

 

its just the way the circuits in ram work that to keep it stable the latency needs to be increased to support higher frequencies

you need to balance the two otherwise you get instability and memory errors

[vanished]

I don't think that's the case, because if it is, then what is the point of having faster memory?

Well, you can get 1600 CL11, and 1600 CL9, for example.  The latter is better overall, but you could take that 1600 CL11 and down clock it to 1333 for example and probably change timings to CL9

[Raytsou]

Well, you can get 1600 CL11, and 1600 CL9, for example.  The latter is better overall, but you could take that 1600 CL11 and down clock it to 1333 for example and probably change timings to CL9

That wasn't really what I meant. I meant like, why would you choose say, DDR3-2400 CAS10 over DDR-1600 CAS 9, but it's fine, @Enderman explained it just fine.

[Glenwing]

Why does it seem that the higher the frequency of the ram, the higher the latency? Isn't latency the delay between the cpu and the ram? Wouldn't that mean that higher clock speed should lower frequency? This is something I never understood despite considering myself a "techie". Every I look, people just say, "get DDR3-1600 CAS 9, it's good enough."

 

The latency is measured in cycles, rather than time units. So it appears that higher frequency RAM has "higher" latency, but it doesn't in reality. Even if your latency time is exactly the same, higher frequency means more RAM cycles will pass during that amount of time, so the latency number "increases" since it's measured in cycles.

 

DDR3 at 1600MHz is 1600 million cycles per second (1.6 billion). CAS latency of 8 means the latency is 8 cycles. At 1.6 billion per second, each individual cycle takes 0.625ns. 8 cycles of latency would be 5.0ns.

 

DDR3 at 2400MHz CAS 11 is 0.41667ns per cycle, and 11 cycles is 4.58333ns of latency. So as you can see the 2400MHz RAM with CAS latency 11 actually has slightly lower latency than 1600MHz CAS 8 even though the number appears higher.

[jjohnthedon1]

The latency is measured in cycles, rather than time units. So it appears that higher frequency RAM has "higher" latency, but it doesn't in reality. Even if your latency time is exactly the same, higher frequency means more RAM cycles will pass during that amount of time, so the latency number "increases" since it's measured in cycles.

DDR3 at 1600MHz is 1600 million cycles per second (1.6 billion). CAS latency of 8 means the latency is 8 cycles. At 1.6 billion per second, each individual cycle takes 0.625ns. 8 cycles of latency would be 5.0ns.

DDR3 at 2400MHz CAS 11 is 0.41667ns per cycle, and 11 cycles is 4.58333ns of latency. So as you can see the 2400MHz RAM with CAS latency 11 actually has slightly lower latency than 1600MHz CAS 8 even though the number appears higher.

bingo

[PrimeSonic]

When comparing RAM, you can use this quick and dirty method to see which one is actually doing more work.

Take the frequency and divide it by the latency.

The higher the resulting number, the more you're getting out of the RAM module.

Don't try to assign any real meaning to that number since it is a huge simplification, but if you're comparing two modules with different frequencies and latencies, this will let you get a rough idea of which one will do more than the other.

[Raytsou]

The latency is measured in cycles, rather than time units. So it appears that higher frequency RAM has "higher" latency, but it doesn't in reality. Even if your latency time is exactly the same, higher frequency means more RAM cycles will pass during that amount of time, so the latency number "increases" since it's measured in cycles.

 

DDR3 at 1600MHz is 1600 million cycles per second (1.6 billion). CAS latency of 8 means the latency is 8 cycles. At 1.6 billion per second, each individual cycle takes 0.625ns. 8 cycles of latency would be 5.0ns.

 

DDR3 at 2400MHz CAS 11 is 0.41667ns per cycle, and 11 cycles is 4.58333ns of latency. So as you can see the 2400MHz RAM with CAS latency 11 actually has slightly lower latency than 1600MHz CAS 8 even though the number appears higher.

Alright, so how is it counted when I see latency numbers like "9-9-9-24-2N"?

[JustCallMeVlad]

DDR4 4000 Master Race

[App4that]

DDR4 4000 Master Race

Have fun with those spread sheets, I'll stick to games LOL.

[JustCallMeVlad]

Have fun with those spread sheets, I'll stick to games LOL.

I'm sure BF4 will be fantastic with these chips

[App4that]

I'm sure BF4 will be fantastic with these chips

Riiiight LOL.

 

[JustCallMeVlad]

Riiiight LOL.

https://www.youtube.com/watch?v=utWnjA4NzSA

I don't see any Skylake comparisons in that video. It's X99 vs Z97 so keep talking out your ass

[App4that]

I don't see any Skylake comparisons in that video. It's X99 vs Z97.

Because a rebranded 4790K won't change the outcome? You know I'm just kidding right?

[JustCallMeVlad]

Because a rebranded 4790K won't change the outcome? You know I'm just kidding right?

So a 6700K is a rebranded 4790K now? Lol

[App4that]

So a 6700K is a rebranded 4790K now? Lol

No, I'm just having fun. Jumped over to your topic.

[JustCallMeVlad]

No, I'm just having fun. Jumped over to your topic.

Oh so you be trollin... Nicely done sir

[Glenwing]

Alright, so how is it counted when I see latency numbers like "9-9-9-24-2N"?

It's honestly best not to even worry about it, given that it doesn't have any meaningful effect on performance.

[Nena Trinity]

i made guide!

[Blackie Sheen]

I understand that, but I'm asking why does higher frequency ram have higher latency compared to lower frequency ram?

The reason is simple: Stability. In order, for the system to be stable, they must increase the latency when they increase the ram's frequency

[Raytsou]

 

It's honestly best not to even worry about it, given that it doesn't have any meaningful effect on performance.

Well, I want to know because I'm curious, not because I need to.

 

The reason is simple: Stability. In order, for the system to be stable, they must increase the latency when they increase the ram's frequency

That's what I though too until I thought about it. Wouldn't the speed increase of increasing the frequency be cancelled out by the latency increase? You can argue that the frequency increase more than the latency, but it just didn't make sense from an efficiency standpoint.

 

DDR4 4000 Master Race

Have fun with those spread sheets, I'll stick to games LOL.

Please keep this on topic. There's a PM function if you wanna argue over pointless things.