If your definition of 64-bit is a 32-bit operating system around a 64-bit chip, then the G5 is a 64-bit platform. Mac OS X 10.2.7 (and the upcoming 10.3) is not a 64-bit operating system. This is particularly frustrating because Apple's marketing machine has very carefully crafted their message to make a reasonable person believe the operating system is 64-bit, especially if you download and read Power Mac G5 Tech Overview (PDF). Apple says about the G5 version of Mac OS X that it "runs all of your software -- and runs it faster -- with a version of Mac OS X Jaguar specially tuned for the PowerPC G5 processor, providing a seamless transition to 64-bit power." That's only the beginning of the smoke and mirrors. The 64-bit power only gives users two things: the operating system can address up to 8GB of RAM, though user programs are still limited to 4GB, and some of the G5 numerical hardware is available with a special version of GCC (3.3). That is very far from what I thought. In fact, we returned the G5 we got last week for a full refund (didn't have to pay the 10% open box fee either), after about 2 hours on the phone. Buyer beware.