So, I have an old machine. It still does mostly all I want, but I'd like to put some more RAM into it. According to UserBenchmark, I have one slot out of four used, and it holds an unknown 8Gb DIMM DDR3 stick that claims to be 3200 Mhz, but is clocking at 1600 Mhz. (I frankly believe the latter is a more correct assessment, based on what I know about DDR3.)
My questions:
1) DDR3 RAM sticks are at least 7 years old (released before Q4 of 2015). You can still get them cheap. DDR4s aren't too pricey, though. Can I mix the two, or is it better to stick with one?
2) Needless to say, the motherboard is contemporaneous with the RAM. Should I even be bothering to think about the DDR4s?
3) Can anyone recommend a reliable site to get RAM? I had one bookmarked, but I've lost it.