Differing RAM sticks in ThinkPad E490

[PaddyC13]

Hi Folks,

 

Hopefully this is a quick question and I apologise for my lack of knowledge here.

 

I have inherited what is essentially a new a ThinkPad E490 laptop with an Intel i7-8565U (4 cores, 8 threads). The machine came with 32GB RAM (2 x 16GB) and in the main works well. I have upgraded the SSD to a Samsung 970 PRO 512GB and this works fine.

 

My concern relates to the RAM as the two sticks are different. The first is:

 

Crucial 16GB DDR4-2666 SODIMM 1.2V CL19

CT16G4SFD8266.M16FH

 

The other is:

 

SK Hynix 16GB 2Rx8

PC4-2400T-SE1-11

HMA82GS6AFR8N-UH NO AC 1715

The Lenovo specification sheet for this laptop states that RAM will run at 2400 due to an “Intel limitation” - whatever that is? This would suggest the Crucial RAM will run below it’s maximum speed of 2666. This is confirmed by CPU-Z.

 

https://psref.lenovo.com/syspool/Sys/PDF/ThinkPad/ThinkPad_E490/ThinkPad_E490_Spec.pdf

 

My concern is around the fact that the Crucial RAM is unbuffered whereas the SK is not (if I am reading their specs correctly).

 

Is this anything to worry about? Should the sticks match for best results?
 

Any advice would be appreciated.

 

Kind regards 

 

Paddy

UK

 

[Eigenvektor]

The i7-8565U officially only supports up to 2400 MHz RAM, so that's your Intel limitation:

https://ark.intel.com/content/www/us/en/ark/products/149091/intel-core-i78565u-processor-8m-cache-up-to-4-60-ghz.html

(Look at "Memory types")

 

Mixing different sticks isn't ideal, but if it works, there's not much to worry about. If you mix different speeds, it'll always run at the speed of the slowest stick unless you overclock, which is usually not an option in a laptop. The CPUs memory controller can only run at one speed at a time.

 

~edit: Also, pretty sure both of these modules are unbuffered. Buffered (or registered) RAM is something you typically only find in servers and is more expensive.

 

 

[PaddyC13]

Hi @Eigenvektor

 

Thank you for your swift and informative reply. Really appreciate you clearing up the "Intel limitation".

 

Reading the Crucial website, they do not recommend mixing memory sticks but I was not sure if that was just to make more money! 

 

May you, or someone else can clear up a couple of other things for me.  On the Crucial website they list these two sticks (and others) as compatible with the ThinkPad E490.

 

Crucial 16GB DDR4-2666 SODIMM
CT16G4SFD8266
https://uk.crucial.com/memory/ddr4/ct16g4sfd8266/ct13998775

Crucial 16GB DDR4-2666 SODIMM
CT16G4SFRA266
https://uk.crucial.com/memory/ddr4/ct16g4sfra266/ct18629266
 

For the life of me, I cannot see what the difference is - can you clarify?

 

My next question is about maximum memory. I get the dual vs. single channel issue and fortunately the E490 has two slots. However, if you have both slots occupied with 16GB sticks (32GB total) BUT your use case means you never go beyond 16GB (I am not gamer or high end user anymore) will the computer only be using one stick all the time? The second stick will effectively be sat there doing nothing?

 

Would you (in theory) get better performance by having less total memory (16GB say), but with two 8GB sticks?

 

Once again, thank you for your help.

 

Kind regards

 

Paddy

UK

 

[PaddyC13]

Hi @Eigenvektor

 

OK, I chatted with Crucial about the above two modules:

 

Crucial 16GB DDR4-2666 SODIMM
CT16G4SFD8266
https://uk.crucial.com/memory/ddr4/ct16g4sfd8266/ct13998775

Crucial 16GB DDR4-2666 SODIMM
CT16G4SFRA266
https://uk.crucial.com/memory/ddr4/ct16g4sfra266/ct18629266

 

According to the agent, the CT16G4SFD8266 part comes with dual ranked RAM whereas CT16G4SFRA266 comes with both single and dual rank RAM. In terms of performance (speed), the agent said CT16G4SFRA266 is the one to go for.

 

As for my second question, I am not sure I got a clear answer (confusion on their part). If they did understand the question:

 

Does 2x8GB (16GB total) performance faster than 2x16GB (32GB total) when memory use does not exceed 16GB?

 

The agent said that there would be no difference unless you exceed 16GB of RAM use. I assume this means that RAM use in interleaved on a PC and data is stored on either stick as the computer runs.

 

Many thanks

 

Paddy

UK

 

[Eigenvektor]

That's a lot of questions Let my try to answer them as much as I can.

 

On 1/9/2022 at 3:28 PM, PaddyC13 said:

Reading the Crucial website, they do not recommend mixing memory sticks but I was not sure if that was just to make more money! 

Mixing memory sticks is a bit of a gamble. It usually works fine, but it may not. I think it is less of an issue when your memory is running within JEDEC specifications (as 2400 MHz should). But when you're using XMP (which is technically an overclock, e.g. to get 3600 MHz), then there's a higher likelihood you won't actually be able to reach the rated speed when mixing. Which is why it is usually recommend to get a set rather than individual sticks. But if it works, it works.

 

On 1/9/2022 at 3:28 PM, PaddyC13 said:

I get the dual vs. single channel issue and fortunately the E490 has two slots. However, if you have both slots occupied with 16GB sticks (32GB total) BUT your use case means you never go beyond 16GB (I am not gamer or high end user anymore) will the computer only be using one stick all the time? The second stick will effectively be sat there doing nothing? Would you (in theory) get better performance by having less total memory (16GB say), but with two 8GB sticks?

Dual channel is a bit like RAID 0. The CPU will distribute data across both sticks, so it can access both of them simultaneously to increase bandwidth. If you're using e.g. 2 GB of memory, the sticks should hold about 1GB each. So it doesn't matter how much memory you use, you always get the dual channel benefit.

 

5 hours ago, PaddyC13 said:

According to the agent, the CT16G4SFD8266 part comes with dual ranked RAM whereas CT16G4SFRA266 comes with both single and dual rank RAM. In terms of performance (speed), the agent said CT16G4SFRA266 is the one to go for.

Dual channel increases bandwidth, while dual rank lowers latency. Both of these can help increase performance. Lower latency is mostly beneficial for gaming and you're unlikely to notice any difference outside of benchmarks otherwise. Dual channel is more likely to help with other things as well (e.g. productivity tasks).

 

I think dual rank has some drawbacks when it comes to overclocking, which might be why the agent recommended the single rank one, not sure. Based on what you said, my guess is it won't make any noticeable difference to you, so just get whatever is cheaper. Even for games we're maybe talking 5% performance difference in some of them.

 

5 hours ago, PaddyC13 said:

The agent said that there would be no difference unless you exceed 16GB of RAM use. I assume this means that RAM use in interleaved on a PC and data is stored on either stick as the computer runs.

Yep. If you never need more than 16 GB, having 32 GB has no performance penalty, just a cost penalty

 

On the other hand, if you "only" have 16 GB and need more than that, your PC will start to swap, which is usually very noticeable. With a fast SSD it is not as bad as with a HDD, but things can still slow to a crawl.

 

That being said, having extra memory may give you better performance, since it allows Windows to use more of it as cache, which can speed things up (to a certain point). But in terms of cost/performance, overspending on memory is probably not worth it.

[PaddyC13]

Hi @Eigenvektor

 

Thank you for your help. I have ordered a new RAM upgrade from Crucial so the sticks will match going forward. I have also ordered some new thermal paste to give my laptops a wee thermal spa day!

 

Many thanks

 

Paddy

UK