Is it REALLY okay to mix RAM?

[paltz.ky]

Hi guys, this is my first time posting here. I'm sorry if I post this in the wrong section.

So I am doing research for my future PC build, and since I don't have any tech background and inexperienced I try to read some article about dos and don'ts about picking RAM.
There's some source that says it is okay to mix RAM IF they compatible with each other. But I am not really sure what they mean with "compatible with each other".

Let's say I pick 2 random RAM

RAM #1

Part No.	CMSO8GX4M1A2133C15
Capacity	8GB (1x 8GB)
Brand	Corsair
Speed	DDR4-2133 - 2133MT/s - PC4-17000
Voltage	1.2V
Technology	DDR4
Error Correction	Non-ECC
Signal Processing	Unbuffered
Form Factor	260-pin SODIMM

RAM #2

Part No.	M471A5244CB0-CRC
Capacity	4GB (1x 4GB)
Brand	Samsung
Speed	DDR4-2400 - 2400MT/s - PC4-19200
Voltage	1.2V
Technology	DDR4
Error Correction	Non-ECC
Signal Processing	Unbuffered
Form Factor	260-pin SODIMM
Ranks	Single rank

From what I know so far, it's okay as long they have the same technology (DDR4), and they will work with the lowest speed (since RAM#1 have lower speed of 2133MT/s I assume it will work at this speed)
Is there any other effect if I use those 2 ram I mentioned above? I know that it's better if we use 2 identical RAM but I just want to know more about this problem.

Thanks.

[Daniel Z.]

They should be fine. BTW those are laptop ram sticks, not desktop

[Eigenvektor]

Ideally you should pick RAM that has the same clock frequency and latency. Mixing sticks usually works (no guarantees though), but as you said, they'll run at the slowest common speed and highest common latency.

[WereCatf]

5 minutes ago, paltz.ky said:

There's some source that says it is okay to mix RAM IF they compatible with each other. But I am not really sure what they mean with "compatible with each other"

There's no 100% guarantee, no matter how one spins things, that mixed RAM will work. That said, in the nearly 30 years I've been messing around with PCs, I have yet to encounter a situation where mixing RAM didn't work.

[paltz.ky]

55 minutes ago, Daniel Z. said:

They should be fine. BTW those are laptop ram sticks, not desktop

 

54 minutes ago, Eigenvektor said:

Ideally you should pick RAM that has the same clock frequency and latency. Mixing sticks usually works (no guarantees though), but as you said, they'll run at the slowest common speed and highest common latency.

 

53 minutes ago, WereCatf said:

There's no 100% guarantee, no matter how one spins things, that mixed RAM will work. That said, in the nearly 30 years I've been messing around with PCs, I have yet to encounter a situation where mixing RAM didn't work.

Thanks for the answer Daniel, Eigenvektor, and WereCatf. Yeah I just picked 2 random model as an example. I haven't decided yet which RAM stick I'm going to pick for my future desktop build, still need to do more research first  So I guess the only way to find out will they really work is by trying them? I'll make sure to buy identical RAM stick for my future build then for optimal result.

Thanks for sharing your knowledge guys