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Cas Latencies Through Time

E

Exitwound

Limp Gawd
Joined
Jun 30, 2004
Messages
164
I can't find a direct answer to this after a while searching both here and the rest of the net, so I'll just ask and see if you can enlighten me.

Why have CAS Latencies increased over the last few generations of memory? It seems that CAS 2 and 3 were common in DDR ram, but now I see a lot of CAS 5 and 6 and 8 timings much more frequently in DDR2 and 3.

Maybe I'm mistaken, but this is why I'm asking.

Thanks!
 
DDR2 and DDR3 each run at significantly higher frequencies compared to the previous generation. The added latency is partially due to changes in the technology and also due to the fact that the memory simply cannot maintain such low latencies with very high speeds.
 
I have also have a couple questions regarding latencies.

1. Would there be any noticeable real life (not benchmarking) performance increase from like 9 9 9 24 to 7 7 7 20?
2. If so, then what areas would it be noticeable in? Multitasking? Gaming? Encoding?
3. Would there be any chance of holding "low" timings like 7 when overclocking an I7 to say 3.6-3.8GHz?

The reason I ask is there are some pretty big price increases that seem purely based off of latencies.

I'm trying to decide on a 6GB DDR3 kit for my I7 build, but I don't want to spend unnecessary money if I'm getting no gain from it.

Thanks
 
1. Not really.
2. NA
3. Yes, since the memory speed is independent of the CPU, your CPU speed will have no effect on latencies.
 
Mike Clements said:
3. Yes, since the memory speed is independent of the CPU, your CPU speed will have no effect on latencies.
Click to expand...

That's not necessarily true. Unless you're dealing with a 965EE, overclocking the CPU will require raising the base clock, which will also raise the minimum speed the RAM will run at, and that can affect the latencies that the memory will be able to run at. However, in practice, any decent set of DDR3 shouldn't have any issues with that.
 
So in terms of ddr2 and ddr3, what cas latencies are most desirable and how much impact do they really have? Any links to comparative articles?
 
The lower the better as long as it works.
However you will only see a performance improvement when the memory latency is already a bottleneck.
 
Zero82z said:
That's not necessarily true. Unless you're dealing with a 965EE, overclocking the CPU will require raising the base clock, which will also raise the minimum speed the RAM will run at, and that can affect the latencies that the memory will be able to run at. However, in practice, any decent set of DDR3 shouldn't have any issues with that.
Click to expand...
This is not correct. Intel unlocked the memory multipliers on the retail 920/940 CPUs. So, you can use different memory dividers with any of the 3 i7 CPUs independently CPU frequency and without changing the BClock..
 
Mike Clements said:
This is not correct. Intel unlocked the memory multipliers on the retail 920/940 CPUs. So, you can use different memory dividers with any of the 3 i7 CPUs independently CPU frequency and without changing the BClock..
Click to expand...

I thought there were still certain dividers that you have to choose from. But anyway, isn't there still a minimum divider you can run?
 
IIRC, it runs 8-14 but it will also depend on the BIOS and the specific MOBO you have. Some are more versatile than others at this time.
 
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