Late 2009 - Upgrading RAM

I'd like to keep this late 2009 model 27" iMac (11,1) up to date to keep it longer. I was wondering, how many RAM sticks do I have in it right now if I have 4GB? If I upgrade RAM to 16GB, am I allowed to mix? $100 for 16GB ram at OWC website isn't a bad price.

Crucial website is showing I have 2x4GB sticks, and can get 2 more for $48.

I remember spending $100 for 512MB RAM!

GGJstudios said:

Sure.

Click to expand...

That doesn't sound to confident.

OWC a good brand, or just go with Crucial?

Thank you!