Mixing soldered and replaceable RAM works, but match speeds

Yes, you can mix them, but the whole system runs at the slowest stick’s speed.

If you pair a fast soldered module with a slower replaceable one, the fast RAM slows down to match. Worse, if they’re different sizes or timings, you might lose dual-channel performance for some of the memory, which hurts speed in memory-heavy tasks.

The safest bet is to buy a replaceable stick that matches the soldered module’s speed (MHz) and CAS latency (CL). Check your laptop’s specs or use CPU-Z to see what’s already in there. If you can’t find an exact match, at least aim for the same speed — the timing will usually work out okay.

Otherwise, you’re leaving performance on the table for no good reason.