OWC Guide: Find out what memory your Power Mac G5 uses
  1. Click the Apple in the top left corner of the Mac OS X menu bar.
  2. Select "About this Mac".
  3. The "About this Mac" pane will appear with processor and memory information.

About this Mac example with the processor highlighted in red:

About Power Mac G5 4 x 2.5GHz

  1. Click the "More Info" button to launch "System Profiler".
  2. Your Power Mac G5 uses PC4200 if your "System Profiler" displays a "Total Number Of Cores" line.
  3. Your Power Mac G5 uses PC3200 if you DO NOT see the "Cores" line in "System Profiler".
System Profiler example with "Core" line displayed: