speed vs cl..

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yasserBasha

yasserBasha

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Mar 23, 2013
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hi guys
So i'm building my new pc and decided to go with FX-8350 for serious OC and heavy gaming and multitasking, but some issue arouse regarding ram :

I basically want to get 16gb (2x8) and i noticed differences between speeds and CL(number)......some told me the less CL the faster the ram and other told me that speed is what matters
so now i have two options of ram :
1- RAM 2133 CL11
2- Ram 1600 CL7

which one should i get
appreciate all of you guys
Thanks in advance
 
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noreaster

noreaster

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May 30, 2012
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Okay, both are important in determining overall performance of RAM. The speed is how many cycles that memory performs in one (1) second (or Hertz (Hz) where 1600MHz means 1,600,000 cycles per second) whereas the CL (CAS Latency) is the number of cycles that memory requires to complete an operation.
To compare the performance I divide the speed by the latency; so in your case you would have:
1- 2133MHz/11CL=193.9Mop/s (mega operations per second (my unofficial unit of performance))
2- 1600MHz/9CL=177.7Mop/s

so in this case the first option would be more favorable. Understand however that the 2133MHz @ CL11 is what the memory is rated for, meaning it should perform at this level with no problems (from the memory at least) but your CPU/Motherboard does not natively support this speed meaning it must "overclock" to reach it. In other words, you have less headroom with the first option to go higher than rated speed but it should perform more stably at that speed than the second option overclocked to 2133MHz @ CL11.

Clear as mud right?
 
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R

raytseng

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May 15, 2012
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There's some complexity that you have to normalize for.

The 2133 RAM rated at 2133 11CL, probably can use a different CL when it's being run slower at 1600.

So if you have the ability to see the SPD settings, then you can see what are it's timing settings at 1600. Likely it will decrease. Then you can compare apples/apples. It's up to you then what speed you want to run the RAM at.

You can also do the math and estimate whether the RAM can meet the reduced CL when the clock is slower, but the SPD settings is more authoritative as the manufacturer's approved settings.

math:
clock times (apologize in advance if I am off by my metric prefix):
2133Mhz =1sec/2133M= 46.8 picosecond per cycle
1600Mhz = 62.5 ps per cycle.

11 clocks at 2133Mhz=515 ps

7 clocks at 1600Mhz=437.5ps
9clocks at 1600Mhz=562ps

So, if the speed ratings represent the fastest possible settings, the order of speed in you RAM is
7CL@1600Mhz
11CL@2133Mhz (but check what is the rating @1600Mhz)
9CL@1600Mhz

 
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