RAM Buying Problem

Yeah. One working instance out of probably 4+ billion PCs in the world is not a case of "It (always) works!". Conversely, one failing instance from the same subset is not a case of "It (always) fails!".

The key idea here is that you need to do the research on what your system is capable of, what your BIOS / UEFI settings will allow you to manipulate as needed, and whether you want to go through the hassle or not.

• If you're new to this sort of thing, it's generally recommended that you buy a matched set 'kit' to save you any potential headaches as the system tries to manage the RAM and potentially causes instability.
  
  
• If you know what you're doing, and have the appropriate tools (aka pertinent BIOS / UEFI settings), you can do it yourself.
  
  
• If you don't care about performance, and understand that mixed RAM will default to the lowest common denominator, aka using the stable settings from the 'slowest' RAM, to standardize processing operations through all DIMMs, then you can also mix and match (this is without manipulation in the BIOS . UEFI to optimize them).

NavyLCDR said:

It runs at the speed of the slowest RAM installed.

Click to expand...

It'd be nice if that was always true.

I'm unconvinced.

johnlgalt said:

• If you don't care about performance, and understand that mixed RAM will default to the lowest common denominator, aka using the stable settings from the 'slowest' RAM, to standardize processing operations through all DIMMs, then you can also mix and match (this is without manipulation in the BIOS . UEFI to optimize them).

Click to expand...

That's the part some here claim don't exist, but outside the bubble of their support they'll find their "facts" don't match reality.

Anyway, I'm not concerned about nay-sayer cause some seem to be allergic to facts anyway, so....

We're looking "Memory Kit"

You didn't specify which memory module you already have.
Micron/Crucial has "Refresh Cycle Time (tRFC)" less. It's probably not a big deal.

Some of new-ish laptops have part of RAM soldered with one or more free slots. those are particularly difficult to match and laptop manufacturers usually make them so "special" that best option isto by RAM from them directly for inflated price. Just couple of month ago I had fight with friend's expensive Lenovo. Apparently it had Crucial DDR4 3200MHz 16GB soldered in it. Although Cruical has a large and probably best list to look for compatible modules only 3rd stick from 3 recommended worked satisfactory, first one not at all. It took a week or more to exchange between tries. Problem is BIOS too, as with most laptops options are poor and difficult to set manually.

Intel NUC ordered from Crucial and got exact same part number of installed ram