Mixing soldered and socketed RAM is a gamble.

Yes, it can cause performance issues, especially if the modules have different speeds, timings, or capacities.

Most modern laptops with soldered RAM allow you to add a stick in the open slot, but the system will default to the slower module’s speed and timings. That means your fast soldered RAM might downclock to match a slower stick. You lose the speed advantage. Also, the memory controller might run in flex mode (asymmetric dual-channel) if capacities don’t match. You get dual-channel for the matched portion and single-channel for the rest — better than single-channel alone, but not as good as fully matched RAM.

If you’re just browsing and doing office work, you probably won’t notice. For gaming or heavy multitasking, the hit can be 5-15%. Not catastrophic, but not ideal.

Your best bet: buy a stick with the same specs (speed, CAS latency) as the soldered RAM, or at least as close as possible. Check the system’s support page for validated upgrades.

Future You will thank you for not cheaping out on that extra ten bucks.