Well, in order for me to really help I need to know a few things:
What kind of Mac computer did you get?
Is it an old Mac or a new Mac (if the specs on your Serial code are accurate then it's a 20" model which hasn't been actually made in several years now, which is important to knowing what type of RAM you need to buy)?
How much RAM do you have now (I'm taking a stab in the dark and saying 4 or
?
Honestly, if you're computer is an older model of Mac, you won't be able to purchase RAM for your computer. Older Macs run on DDR2 RAM, and right now they're about to discontinue DDR3 RAM (meaning DDR2 is way out of date). The only way you'll be able to upgrade that is by taking it into an Apple Store and specifying what you want done. Especially since you can't take apart your computer yourself to upgrade it.
If your computer IS new and you can buy RAM for it, you'll need to buy 2 sets of 8GBs of Ram. There are 2 slots for macs to put Ram in, in most cases it's 4Gb and 4Gb. The trick is both sides have to be even otherwise you're hindering your computer rather than helping it.
Macs are complicated. I'm not overly versed in them, but my boyfriend has been studying up on them for a little while now and that's where I've sought this information out. Once I have the answers to those questions can I help you determine your RAM capabilities.
My boyfriend speculated that you had an older Model of Mac due to the 20" bit on the bottom, as they haven't made a screen that size in a while.
Either way, I recommend Corsair for memory, as it's efficient and they sell RAM for Macs specifically, but it likely won't be too cheap. I fear that cutting corners with RAM for the Mac could be problematic, so I would definitely recommend getting it from a big-namer like Corsair if you do end up getting extra RAM, but let's just see what your computer is before we go off buying RAM.
If you're really unsure, I highly recommend taking it to an Apple store and just asking there about it.
