The processor makes everything you do on your Mac possible, from loading text documents to running an iMovie effect. Because the processor’s performance affects every aspect of a Mac, we’re always in favor of an upgrade – although, sadly, you don’t have a lot of options. No one currently makes processor upgrades for G5 or Intel Macs.  Instead, a range of G4 upgrades exist for Macs that originally shipped with that chip. If you can make a big jump in speed – say from 400MHz to 1.8 GHz consider the upgrade for your G4.
What’s more, we don’t know whether processor upgrades will conflict with Leopard. We suspect that there may be a few initial hiccups. Every processor maker we contacted anticipates that, as with Mac OS 10.4, Apple won’t officially support processor upgrades, but that a machine with an upgraded processor should be able to run Leopard. And when necessary, vendors should offer fixes.
TO INSTALL: You’ll need to remove the heat  sink– and possibly also a fan – that  cool the  original chip. Theses are usually held in place with a metal latch. Once exposed, most processors pop put of their sockets after you’ve lifted a release lever. Gently set the new processor into position and reset the lever to secure it in place. The processor upgrade may include its own heat sink. Depending on the instructions provided, attach the new heat sink or reconnect the old one.

WHO’S IT FOR:
G4 owners with a speed boost potential.

PRIOITY: Medium

OPTIONS: OWC Mercury Extreme ($199 to $259.99, www.otherworldcomputing.com).
NewerTech MAXPower ($249 to $699, www.newertech.com)