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RAM latency vs frequency in mhz

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#1 ksinley


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Posted 08 August 2015 - 01:22 PM

Ok, I am sure there is some questions relating to this but I cannot find a direct answer to what I am finding.   I am looking at buying  ram, probably 16 Ghz, just waiting on a sale for under $70 and such over time. 


To get to the main point, what would be better, ram with all specs the same except for the frequency in mhz and latency,  1600 Mhz with CAS latency of 9 or 2133 Mhz with CAS latency of 11,


Also if latency is better overall than mhz,  would it be worth the little extra money to get CAS 7 types? 


To narrow down the possible solutions, I am just gonna build a decent gaming type computer, I may or may not game on it but I want it to last for the next 6 - 7 years and still be a decent build.  I wont game much but I may try some out from time to time, I do plan on trying out the witcher 3 but not sure if its good on pc or better with PS4.  I am gonna get a SSD drive too for speed and a decent video card with 4 GB ram in it,  as well as i7 4790k processor when I do build it.  But I will wait until theres sales on them to save some money.




Ok I have found an equation via wikipedia that I think will answer not only mine but a lot of peoples questions based on latency and frequency. 


The formula is:

(CAS / Frequency (in Mhz) x 1000 = X  (in Nanoseconds)


So to compare the 2,


(9 / 1600) x 1000 = 5.625 ns


(11 / 2133) x 1000 = 5.157 ns


So in comparison, the 2133 Mhz would be faster.  But by only about half a nanosecond.


If im wrong please correct me but this is what I think would be better.

Edited by ksinley, 09 August 2015 - 12:41 PM.

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#2 LFos42


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Posted 08 August 2015 - 02:42 PM

I would throw into the mix what the specific brand, and memory specs (reviews on line for issues and specs for compatability), what your motherboard is rated for, and how much you want to overclock. I think I'd jump at the 2133 MHz with the latency of 11, if your system will stay stable for the OC.  I'd check specifically the memory you're buying and how it's rated.  CAS 7 is really nice, if you can get it.  I'm still kicking myself for not getting more memory when I found a nice low latency set (a quad set, instead of a dual set with low latency.)  They OC rock stable for a good set, and can really be pushed.  If it's an older motherboard, and it can't handle 2133, then the lower CAS 1600 definitely.

#3 ksinley

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Posted 09 August 2015 - 11:49 AM

Yea, I was just assuming 2 of the same brand,  assuming the motherboard is rated for both of those.  I dont plan to overclock it.  But I just edited with a formula which I think can greatly answer my question on it.  Since im sure the ultimate lower nanoseconds is what counts with gaming considering you have a good brand.

#4 jonuk76


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Posted 09 August 2015 - 04:00 PM

There's a good table in Wikipedia showing the computed access time in nanoseconds for various CAS latencies at different speeds.  Maybe helpful?



#5 yu gnomi

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Posted 10 August 2015 - 01:25 AM

If you are going to build with an Intel Haswell processor, look at this http://www.anandtech.com/show/7364/memory-scaling-on-haswell


Info is probably valid for Broadwell, but I don't know about Skylake.

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