If you startup disk is nearly full, your Mac's performance will degrade considerably. Mac OS X makes extensive use of Virtual Memory (VM), which requires free disk space on your startup disk, aka your boot volume. Maintain ample free space on your startup disk Install the maximum amount of RAM that your Mac will accept and your budget will allow. Short of buying a new Mac or a processor upgrade, adding RAM is the best way to improve Mac OS X performance.
Optimizing Mac OS X performance RAM, RAM, and more RAM Comprehensive advice on this topic can be found in the 'Performance' chapter of our book Troubleshooting Mac OS X.
Additionally, it provides advice and links to advice for troubleshooting certain Mac OS X performance problems. This FAQ provides recommendations for optimizing Mac® OS X performance.
