[kirbysayshi]

My completely non-scientific observations have found that OS X needs plenty of RAM, like any modern OS. However, any disk I/O task has a huge performance impact on the rest of the system, as described by this article. For example, something like unRARing a file will affect the entire system detrimentally, even if CPU usage is nominal. By affect I mean even the cursor can get jittery, which is normally unheard of on OS X.

This typically affects me in low memory situations, such as less than 100mb of free memory. The effect is most pronounced when switching between browser tabs, which would cause a lot of disk usage... pulling all of that data in and out of non-ram cache.