CAS latency?

[littlepigboy5]

What is CAS latency specifically and why do DDR4 Kits for the most part have higher cas latency than ddr3?

[littlepigboy5]

*bump*

[SansVarnic]

What is CAS latency specifically and why do DDR4 Kits for the most part have higher cas latency than ddr3?

 

 

This might you out.

 

http://www.corsair.com/en-us/blog/2014/september/ddr3_vs_ddr4_synthetic

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And this does a fair job as well.

http://www.tomshardware.com/faq/id-2291218/ddr4-ddr3-breakdown.html

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I'm getting ready for bed otherwise I would give you a quick synopsis myself. Good night LTT. ​

Hope that helps.

 

*edit

Make sure to follow your posts. And mark answered if you satisfied with a reply.

[SteveGrabowski0]

What is CAS latency specifically and why do DDR4 Kits for the most part have higher cas latency than ddr3?

 

CAS latency is a confusing stat for memory that doesn't tell a whole lot on its own about what the latency actually is (e.g. the time between when you request a piece of data and it begins transmitting and similar for writing data). It's kind of ridiculous that the number of clock cycles of CAS latency is the stat people judge RAM latency by when the actual time latency is given by CL/CLOCKSPEED. Higher clockspeed RAM usually has a high CL, but the actual latency is usually pretty similar (and sometimes faster) due to the higher clockspeed. E.g., a CAS 9 DDR3-1600 kit has latency (9 cycle)/(800 MHz) = 11.25 nanosecond (recall 1MHz = 10^6 cycle/second) while a CAS 13 DDR3-2400 kit has latency (13 cycle)/(1200 MHz) = 10.83 nanosecond.

 

The latency isn't just the CAS latency though, as CAS only measures the time it takes to get to the correct column in your array of memory. There is also a delay with getting to the correct row of the array, and a couple of other delays. They behave similarly to CAS latency.

[littlepigboy5]

CAS latency is a confusing stat for memory that doesn't tell a whole lot on its own about what the latency actually is (e.g. the time between when you request a piece of data and it begins transmitting and similar for writing data). It's kind of ridiculous that the number of clock cycles of CAS latency is the stat people judge RAM latency by when the actual time latency is given by CL/CLOCKSPEED. Higher clockspeed RAM usually has a high CL, but the actual latency is usually pretty similar (and sometimes faster) due to the higher clockspeed. E.g., a CAS 9 DDR3-1600 kit has latency (9 cycle)/(800 MHz) = 11.25 nanosecond (recall 1MHz = 10^6 cycle/second) while a CAS 13 DDR3-2400 kit has latency (13 cycle)/(1200 MHz) = 10.83 nanosecond.

 

The latency isn't just the CAS latency though, as CAS only measures the time it takes to get to the correct column in your array of memory. There is also a delay with getting to the correct row of the array, and a couple of other delays. They behave similarly to CAS latency.

thanks, really helpful