But for the up iMacs (not the base models) you can put in third-party RAM. That is what I have always done to avoid Apples high prices on that (except on my laptop, where it is soldered in). But I would caution you about trying to mix in faster RAM, many non-third part. system only take one speed of RAM. That makes the system not only cheaper to build, but often you can tweak some more speed (really latency) out of it.