Apple’s G5: More than a pretty face

Apple’s G5: More than a pretty face

Most modern systems look more at home in a construction trailer than in a corporate machine room or cubicle. The burly, breathable aluminum chassis of the Power Mac G5, however, is a welcome respite from ubiquitous drab sheet metal and injection-molded plastic. Still, a few days after buying a pretty machine, the romance is over. If it doesn’t prove itself superior in all ways to other systems in its price range, IT won’t pen a purchase order for a second one.

At the time of writing, my colleagues at IDG’s photo studio have spent more quality time in the company of a Power Mac G5 than I have. But I did poke at the innards of the Power Mac G5 at two trade shows and during a visit to Apple Computer’s headquarters. If it was an empty head in expensive clothes, I’d know it. It is not — but that’s about all I know at this point.


Onstage demos at the Macworld Creative Pro Conference & Expo highlighted two of the G5’s strong suits: floating-point math and lightning-fast graphics. Apple confessed that in a single-processor configuration, the G5 CPU is slower than a solo Xeon. The Power Mac G5’s turbocharger kicks in when you install the second CPU.

The key to this machine’s success will be throughput. The specs of all of the interconnects — between the two CPUs, between CPUs and memory, to and from the support chip set, and between the chip set and I/O busses — scream by desktop PC standards. Each processor has its own 1GHz bus. Memory bandwidth is 6.4GB per second. The 64-bit expansion bus runs at 133MHz and conforms to the PCI-X standard commonly reserved for servers. The graphics accelerator is fed by an 8x Accelerated Graphics Port (AGP) Pro bus for maximum speed and an ample supply of electrical power. In the Power Mac G5, data does not spend much time on the bench waiting for the bus.

IBM handed Apple the gift of a lifetime with its PowerPC 970 (dubbed G5 by Apple as a follow-on to its current G4) processor. Based on the potent Power4 core used in IBM’s high-performance computers, the 970 is the first PowerPC chip capable of running 64-bit software. By extension, the Power Mac G5 is Apple’s first 64-bit computer, and the first 64-bit desktop machine to hit the market. It can address more memory (the first G5 holds up to 8GB of RAM) and store more and larger floating-point numbers in the CPU. The processor’s internal capacity for data storage (small data blocks called registers) has been markedly expanded, as has the pipeline for instructions awaiting execution.

Apple can’t ask all of its ISVs to rewrite their applications for 64 bits. Many vendors just finished retooling for OS X, a task that required enormous effort. To ease the transition, IBM and Apple built the PowerPC 970 and Panther to operate in bridge mode. In this state, all 32-bit programs benefit from several PowerPC 970 enhancements (such as the larger memory address space) without being rewritten.

In keeping with this commitment to compatibility, Panther is a 32-bit OS. But the Power Mac G5 is designed to do everything in 64 bits. As 64-bit apps emerge, Apple will unleash changes to OS X that take full advantage of the PowerPC 970’s power. It is important to note that the BSD OS, on which OS X is based, has run on several 64-bit architectures for years. A 64-bit edition of OS X won’t require much effort from Apple.

Measuring up

It would be reasonable to expect all of these sprinting electrons to generate a lot of heat; they inevitably do. Pulling that heat out of a chassis normally calls for banks of obnoxiously loud fans. At a normal workload (that is, not rendering frames for Pixar Animation Studio’s sequel to Finding Nemo), Apple claims the machine emits 35 dB of noise. The ceiling fan over my head is louder than that. The proof will be running a Power Mac G5 in an otherwise silent lab.

It’s too early to start heaping praise or finding fault with this machine. It certainly looks great on paper, it demos well, and my brief test drives have me looking forward to giving it a merciless beating. I’m especially curious to see how it measures up to the top-end Xeon, Opteron, and Mac systems already in my lab.

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