Major Causes of Performance Problems
Performance problems typically come from one or more of 5 major areas: algorithms, memory, CPU, disk, and graphics. Granted, that is pretty much everything your program interacts with in the machine. You can use performance tools to look at each aspect of computer performance in isolation to get a better handle on your overall performance issues, even if one problem is causing problems in several categories.
Even though modern machines have vast amounts of memory, RAM is still a scarce resource. Once your app or other apps on the system fill up memory, Mac OS X starts sending memory pages to disk, destroying performance. On iOS devices, your program may be killed outright in low-memory situations. ...