You can’t tell the difference between a dual-processor Power Mac G5 and the new dual CPU, dual core Power Mac G5 Quad from looking. Your software can’t tell the difference, either. But if you could pull up a chair, as I did, and watch closely as professional drivers take the Power Mac G5 Quad around the track, you’ll come away with a new take on PC-priced workstations.I have audio that I recorded during the briefings to chop up and post here. But I think that getting a nod out now to the gearheads among my readership is fitting.Understand that I was impressed by a number of factors that wouldn’t influence a review or a buying decision. The demos were all carried out on Apple’s turf and performed not by marketeers, but by the high-level Apple technical staff who are elbow deep in the technology they were demonstrating. Of the applications used in my briefings, only two–the Shake high-end film/video layering, compositing and workflow tools, and the Aperture pro digital photography suite–were of types familiar enough to me to connect me to Power Mac G5 Quad’s practical performance advantage. Power Mac G5 Quad (known from here on as Quad) is a four-processor Power Mac G5. Period. I point this out because vendors’ implementations of multi-core technology vary in the degree to which multiple cores on one semiconductor die outshines multiple discrete CPUs in one symmetric multiprocessing (SMP) chassis. Quad is indistinguishable from four-way SMP in architecture. Quad’s PowerPC 970 cores are linked together using the same bidirectional bus that interconnects PowerPC 970 CPUs in the dual-processor Power Mac G5. Each dual-core CPU chip in a Quad still has the same single, bidirectional bus that the single-core PowerPC 970 uses, meaning that each pair of cores shares one bus.However, where Power Mac G5 had 512 KB of Level 2 cache per processor, Power Mac G5 Quad has 1 MB of L2 cache per core. You can feel the bump in cache; the PowerPC architecture has always made good use of it, but that win is somewhat muted by the drop in maximum clock speed from 2.7 GHz to 2.5 GHz. That carries with it a reduction in the access speed of the cache and slows the bus to main memory.The performance toll of slower CPUs shows in Apple’s benchmarks, an area in which Apple deserves considerable credit for honesty. The performance gain of a 2.5 GHz Quad over dual-CPU 2.7 GHz Power Mac G5 is, running Apple’s real and well-threaded applications, closer to 60 percent overall than the near-linear gain one might hope for. But the bright side, among many others, is that Apple is able to cool the equivalent of four PowerPC 970 parts without resorting to an external radiator (it still uses a sealed water cooling system). I think the 2.5 and 2.7 GHz PowerPC 970 processors are already overclocked to a degree not seen in other commercial systems. If you choose to be disappointed by 60 percent performance gain instead of 80 percent, try to ground your perspective in the fact that a four-core workstation, ready to roll, list prices out at $3,299. Plant that in your head, folks: $3,299.Yes, but is it a workstation? For that, you must wait. Software Development