Grab your little black medical bag and take a trip into the world of the computer doctors. The key to any diagnosis is isolating the symptoms of your Mac's illness and seeing how they fit the possible causes.

Here are some of the symptoms you may be encountering:

• My Mac is slow when I have a lot of programs running at once. Although a processor upgrade may help, the most important upgrade is RAM. The more main memory you have, the more programs you can run at once and the more quickly they'll all run, especially if you boost each application's individual memory partition.
• My Mac is slow when I copy files over a network. The latest software can go a long way to improving network copy operations, but the differences between LocalTalk connections and either Ethernet or AirPort wireless connections are very noticeable. If slow network copies are ruining your whole day, upgrade your network hardware.
• My Mac is slow when using a Web browser or America Online software. If you have chronic slowdowns when accessing the Internet, this could be a processing or RAM issue. It's also possible that your Internet connection itself could be upgraded — you might go with a more capable modem, a cable modem, or DSL to the Internet, if they're available in your area. If you have a modem connection, you should troubleshoot it first — it's always possible that you're not getting optimum connections with a perfectly capable modem.
• My Power Macintosh is slow. Macs that use the PowerPC processor run optimally with software designed to run on PowerPC machines, called native software. If you have older software (say, five or more years old), it might not run in native mode on your Power Mac, slowing things down quite a bit. (To a lesser extent, the same is true for classic Mac software that you're running on Mac OS X, as well as software that hasn't been optimized for the Power Macintosh G4, if you have such a beast.) Most Power Macs benefit greatly from both increased RAM and some form of cache RAM, so adding a cache memory module might be one way to speed things up.