Which RAM should I buy?

Question

I have an Asus X55LAB, here are the specifications:

• Processor: Intel i5-5200u 2.2 GHz
• RAM: 4 GB DDR3L

The laptop has an accessible 2nd RAM slot. I know I should buy a SODIMM card. I've heard a lot and some of it is contradictory. So, my questions are:

• Is it true that the best option, having a first 4GB DDR3l, is to get another 4 GB DDR3 memory? Supposedly, if you get different sizes then "performance drops"
• What are the real consequences of installing, for example, an 8GB memory in the RAM slot having an original 4GB card? And the same for getting a DDR4 card? Would it even work?
• Does the brand of the memory really matter? I mean, I don't want to pay for an expensive card to get just the same as a cheaper one only because it says "Gamer" in the title and because of the brand.
• Are there any speed/clock issues that I should look for before buying? Or if I make sure of getting a DDR3L memory then I'm okay?

Thanks to all, I appreciate some guidance here.

Answer 1

So for RAM you need the same generation for it to work, that's it. If you get uneven size sticks, the performace will drop when one of the sticks is full (but it will be similar as with one stick of RAM). Brand doesn't really matter although to get XMP working better you do generally want the specs and the brand of the chips to be as close as possible. DDR4 won't fit though since your mobo only supports DDR3(L)