Does it matter CL9 or CL11 when selecting DDR3?

Question

I have an Asus motherboard, H97-E, with G.SKILL's 2X4GB DDR3-1600 CL-9.

I wish to expand to 16GB, but find this excat type, is quite scarce nowadays. BUT a DDR3-1600, CL-11 can be found in stores near by.

Is it possible to combine CL-9, and CL-11 on same motherboard ?

Is my motherboard capable of running a CL-11 ( assuming mixing is not possible, and using only CL-11 )?

Solution 1

CL = Column Address Strobe Latency, which shows the number of clock cycles that pass from when an instruction is given for a particular column and the moment the data is available. In general, the lower the CAS latency the better within a given memory technology.

So, a CL-9 will be faster than a CL-11, all other things being equal.

Your motherboard's manual https://dlcdnets.asus.com/pub/ASUS/mb/LGA1150/H97M-E/E9092_H97M-E.pdf says not to mix memory modules with different latencies.

How much it slows down if you change to all CL-11 may not be noticed. A Tom's Hardware review showed a 2 % slowdown when CL-11 was tested vs CL-9, and that's before other hardware choices were factored in.

Since, with the 2014 design of your motherboard and its H97 chipset, at most you can run an Intel Core i7-5775C or i7-4790K CPU, so the difference won't be earthshaking, or even perceptible.

Solution 2

Is it possible to combine CL-9, and CL-11 on same motherboard ?

Yes; However, the highest latency module, will determine the latency for all modules installed in your system. This means all modules installed would have a CAS (Column Access Strobe) latency of CL-11. However, ASUS does not recommend you mix modules with different CAS latency, nor does ASUS explicitly indicate your motherboard supports that configuration.

Is my motherboard capable of running a module with a CAS latency of CL-11?

Memory compatibility with a motherboard is not determined by the CAS latency of the module typically.

Reference: CAS latency

Solution 3

K7AAY and Ramhound provided good answers.

Another thing to pay attention - the voltage.

You may check your current RAM voltage and buy new stick(s) that need the same voltage.

Otherwise, from my experience, You'll have problems.

Comments

[guyd]

will be as slow as CL9 ? or less?

[Mast]

CL-11 will be slower than CL-9, but as long as you have faster than CL-16 you probably won't notice much. Lower = better.

[guyd]

How can I tell if it is a must to install memory chips in pairs ( some times it is ), meaning - can I but a third ddr3 8GB or only 2X4GB ?

[K7AAY]

Consult your motherboard's manual, downloaded from dlcdnets.asus.com/pub/ASUS/mb/LGA1150/H97M-E/E9092_H97M-E.pd‌​f to find if they recommend installing memory in pairs, as well as other recommendations (e.g., not mixing single-rank and dual-rank DIMMs).

[guyd]

Wow!! Thank you for this pdf. 1.4.2 bullet #3 - says specifically not to mix CL’s, doesnt it?

[J. Shmoe]

Also, to compare latencies, you need to take the max clock rate into account -- the latency is the number of cycles at that rate, but at a lower clock rate, the same delay uses a lower number of cycles, so for example many CL17 DDR4 2400 can also be used as CL15 DDR4 2133.

[Michael]

@Guy.D: I think they are overly pedantic: I mean, the paragraph continues with “we recommend that you install memory modules of the same version or date code (D/C) from the same vendor.” I’ve had very little issues with all kinds of combinations.

[K7AAY]

The manual for the OP's motherboard dlcdnets.asus.com/pub/ASUS/mb/LGA1150/H97M-E/E9092_H97M-E.pd‌​f , says on page 1-7 not to mix memory with different latencies. Do you have an authoritative source within ASUS which says it is acceptable?

[guyd]

@Michael I hope they are. Since I’ll have to buy it online without any after sale support

[Ramhound]

@K7AAY - No; I don't but the modules should still function; I will admit that ASUS does not explicitly indicate mix latency module configuration is even supported. Just because it's recommended doesn't mean it's not supported.

[guyd]

you are most certainly right. while trying to choose an alternative, I cam across several types ( another brand- Hyper-X), while all parameters where the same, voltage can be 1.25v, 1.35v. 1.5v and so on. For my own need- it is 1.5V