Mixing RAM speeds mostly works — but not at full speed

Yes, you can mix RAM speeds with soldered memory, but the whole system will run at the slower stick’s speed.

Laptops with soldered RAM are common now, and adding an extra SODIMM usually works fine — but the memory controller negotiates the lowest common denominator. If your soldered RAM is 3200 MHz and you add a 2666 MHz stick, everything runs at 2666 MHz. The faster stick just gets held back.

Same goes the other way: adding a faster stick to slower soldered memory is a waste of money. You paid for speed you won’t use.

Mixing capacities is less of a problem than mixing speeds, but if you can, try to match the speed (