[SOLVED] RAM and CAS Latency

[ravin_29]

I have HP laptop with existing RAM which is 4GB 2666Mhz and here are the CPU-Z screenshots. If I understand correctly, this RAM is running at 1863 Mhz with CAS latency of 13 at the moment. I am interested to replace this stick with a new single 8GB Stick from Crucial. As per specs it has latency 19
So my question is if I replace it with a new stick where specs say CAS 19, will it operate at CAS 19 or will it switch to 13 if supported at 1800Mhz by JEDEC?
Is CAS latency fixed or does it vary by frequency and if so, is there any specific vendor provided documentation that share this info like memory frequency and CAS latency?

 

[SkyNetRising]

If I understand correctly, this RAM is running at 1863 Mhz with CAS latency of 13 at the moment.

Correct.

So my question is if I replace it with a new stick where specs say CAS 19, will it operate at CAS 19 or will it switch to 13 if supported at 1800Mhz by JEDEC?
Is CAS latency fixed or does it vary by frequency and if so, is there any specific vendor provided documentation that share this info like memory frequency and CAS latency?

Depends on SPD table of the module. Also depends on motherboard chipset and BIOS settings.
If BIOS allows setting ram parameters, then you can manipulate these.
If not, then parameters get set automatically. Automatic configuration doesn't always choose best settings. Main consideration there is usually stability (not max performance).

 

[popatim]

Automatic configuration usually uses the timings from the slowest ram so you may end up with 1863 at cl19. It might be better to get a matched pair of sticks to begin with; if your laptop has two ram sockets that is.

 

[ravin_29]

Thanks.
As per Amazon reviews users are commenting that the RAM can also work at CAS 17 at a specific speed, that made me wonder if 19 would automatically switch to 13 at 1800 as it has done for existing 4GB. But that one is from Samsung.
But Crucial is silent about it. Looks like this data is not available anywhere, I only have to try it out.
I guess my laptop has a limit of 1800 because of A6 APU. There's only 1 slot inside. I remove this 4 GB and insert 8.