Question How different RAM specs need to be to be incompatible?

Aug 22, 2019
I have an i7-5820K processor on Asus X99A motherboard with 16 GB (8GB*2) DDR4-2133 RAM [1]

I'm planning to add another 16GB from the same brand however I cannot find the 2133 Mhz version anymore. The closest I can get is a 2400 MHz which does have different specs on pretty much every parameter. The shop I went to purchase the pair from discouraged me from buying it citing incompatibility but my previous experience suggests it should work since the specs are not VASTLY different.

But I need to be sure. Will RAM [2] work with existing installed RAM [1]

[1] Already installed RAM -

[2] Planning to purchase this one -

PC Tailor

Welcome to the forums my friend!

But I need to be sure. Will RAM [2] work with existing installed RAM [1]
Unfortunately this is a question no one can answer.

RAM modules are ONLY guaranteed in the form sold (from the same pack) regardless as to the make / model / timings / voltages etc. This is because the manufacturing process changes frequently, so the 2 modules can never be guaranteed to work well with one another.

The "ensuring the specs are the same" is only a way of trying to minimise risk, not eliminating it. And even then, you can buy 2 identical modules in spec, and they may not work together. Even if you tried the same modules in an identical system (same MB / CPU etc.). They may work on one, and not the other.

Not saying they never work, just it's a 50/50 gamble, sometimes they do, sometimes they don't. But there is absolutely no way of telling until you simply plug them in and try unfortunately.