Memory latency vs bandwidth for laptops

TechMasterMind · June 29, 2022

So I'm looking at getting some memory for my laptop. 2x8gb kits 2x8 kits, but one is quoted as CL15 2666mhz and one is quoted as CL22 3200mhz - from looking at benchmarks it seems that for every drop of 1 CL you get about 1% performance and a similar 7-8ish% jump for 2666-3200.

However, my laptop is currently running 3200mhz (8gb hence the upgrade) and so I would expect 3200mhz would run fine. But I'm not sure if the CL15 kit will be able to do CL15 out of the box. As I'm not aware of anyway I could lower the timings on my laptop if the timings would not come out of the box at CL15 they would stay that way and I do not want to but the CL15 kit and realise in a few days time on CPU-z its CL20 or something and return it.

Can anyone give me some clarification? Thanks a million in advance for your help! : 3

Levent · June 29, 2022

Whatever kit you get, if its not the same one that is currently in your laptop, it will run at the lowest hardcoded JEDEC spec. Dont be upgrading laptop rams hoping to get lower latency or higher bandwidth. Laptop bioses rarely allow user to run XMP profiles or timings/frequencies other than what was hardcoded in the bios.

TechMasterMind · June 29, 2022

9 minutes ago, Levent said:

Whatever kit you get, if its not the same one that is currently in your laptop, it will run at the lowest hardcoded JEDEC spec. Dont be upgrading laptop rams hoping to get lower latency or higher bandwidth. Laptop bioses rarely allow user to run XMP profiles or timings/frequencies other than what was hardcoded in the bios.

So TL;DR the faster memory in this instance as I have 3200mhz already its more likely to work? And the CL15 will be a memory profile?

mariushm · June 29, 2022

Both the timings and the frequencies are defined in a profile.

BUT the laptop will also have some hardcoded profiles and may override the existing profiles stored in your stick.

Go with higher frequency version, the higher frequency sticks should have multiple profiles, one with the 3200 Mhz and usually a few profiles with lower frequencies (ex 3000 mhz, 2833 mhz , 2666 mhz).

The higher the frequency the more the latency has to be relaxed (so you could say 3200 CL 22 = 3000 CL 20 = 2800 CL 18 = 2666 CL16 )

The laptop's bios will probably default them to 2666 Mhz CL18-20 (or the speed of your current sticks) and the bios may allow you to tweak the timings.

Oh.. you say you currently have 8 GB installed ... is it 4 + 4 or a single stick of 8 GB? If it's just one is the stick removable or soldered to the motherboard? If it's soldered, then it's best to get a stick with same frequency and timings equal or better.

Use CPU-Z or Aida64 (would be more detailed) to get the information about your current ram.

If it's a single stick of ram, you don't need to buy a pair of 8 GB sticks, you could buy just one stick to add to existing one.

It's not required but it would help if you get a stick that has ram chips from the same manufacturer (ex micron, nanya, samsung, hynix) - Aida64 may tell you who made the ram chips but you could also figure it out by looking at actual ram chips.