Mac Pro testing notes

The print layout of the Mac Pro review left me with only about 400 words. I'll use this space to put meat on those bones.

Power: With four 500 GB drives, 4 GB of RAM and an NVIDIA Quadro FX 4500 w/512 MB of GDDR3 RAM, the Mac Pro review unit in my lab idles at just below 200 watts. Maxing out all four cores to 100 percent utilization raised the load to 277-290 watts. I heated up the GPU with eight simultaneous SPECviewperf 8.1 runs and pushed the box close to 300 watts. As many testers note, SPECviewperf is not a measure of CPU or total system performance, but with multiple instances piled high, it does a fine job of keeping four cores pumping with a realistically heavy workload pattern.

In sleep, Mac Pro draws a paltry 7 watts, and the machine wakes fully from sleep in about four seconds. The moral here is to make liberal use of sleep mode.

I had hoped to see a lower quiescent load; Intel's marketing certainly set some exciting expectations, but its claims are always expressed in terms relative to a fuse-blowing quad core Netburst Xeon workstation. I can't speak to the operating power draw of this class of machine--it's gone and good riddance--but the quad Netburst and the original Itanium workstations have been the only systems to trip my shop's breakers. With that as a comparative baseline, yes, Mac Pro is a model of efficiency. But it does not thrill next to Opteron with PowerNow! and Cool and Quiet enabled.

Noise: What noise? Mac Pro's three huge fans spin at low RPMs at maximum load in inhabitable ambient temperature (< 80 degrees Fahrenheit), the heavy gage aluminum chassis is sealed to leakage and vibration, and there are no constrained portals through which air is drawn or exhausted. The sound of Mac Pro's fans is low in frequency and really quite pleasant. In my tests, unidrectional (cardioid) microphones blocked it completely. There was no need to resort to filters in Logic Pro to pull Mac Pro's noise out of vocals and voice-overs.

The entire front and back panels (except where peripheral ports and optical drive covers sit) of Mac Pro are stamped with a honeycomb pattern of holes that creates about 50 percent air permeability. The honeycomb wraps a bit around the top and bottom of the chassis so there is vertical airflow as well. The fan noise is scattered by the chassis rather than focused, so I find that what noise there is doesn't reflect off the walls of a tight working space.

Cooling: Apple figured out how to keep two dual-core PowerPC G5 CPUs ("fast as hell, twice as hot") cool in Power Mac G5 Quad. Mac Pro was a walk in the park after that. Mac Pro has no remnants of PowerPC water cooling and heat piping, but Intel Woodcrest reference motherboards aren't inherently designed for quiet systems. Woodcrest is built to be cooled the good old fashioned way, with buzzy fans strapped to CPU heat sinks, lots of commodity motherboard-controlled fans and one dedicated fan in the power supply. Apple doesn't use ducted cooling as it did with the PowerPC systems in this chassis, but Mac Pro does have two zones through which air is pushed. The upper zone takes care of the expansion card cage, hard and optical drives, power supply and miscellaneous motherboard circuitry.

The lower zone earns my admiration, bordering on awe. Heatsink-mounted fans always struck me as a horrible design. Yes, they sit right on top of the thing that wants cooling, but the airflow is haphazard. In most of the designs with which I'm familiar, the airflow is poorest at the center where the CPU needs it most. Apple's approach is atypical. Mac Pro's heat sinks rise high above the motherboard; I believe they're on risers, but again, without permission from Steve, I won't break open this loaner to find out. Memory sits several inches from the CPUs, and memory (and support components) sits on a pair of removable riser cards that, like the PCI Express expansion cards, stand perpendicular to the motherboard. One strong fan pushes air straight through this alley while the single fan at the rear sucks it out. And of course, you've got the whole chassis acting as a heat sink.

Cooling is a big deal in Macs because Apple will not throttle its CPUs down until they reach critical temperature levels. I have tried many times to push Mac notebooks and desktops into thermal shutdown, but I've never been able to do it. A MacBook Pro in "better performance" mode will (do not try this at home!) ran for several hours wrapped in a comforter. It was practically glowing hot when I unwrapped it, but the benchmarks I had left running showed that the CPU never throttled down. I got confirmation from Apple that this is consistent in Apple designs. To put a twist on Phoenix weather reports, "Macs get hot, but it's a quiet heat." I haven't yet taken Mac Pro down to my 108 degree garage to run sixteen simultaneous SPECcpu processes. That sounds like a weekend thing.

Oddities: I found a number of empty pads for small to moderate pin count surface-mount ICs on the motherboard real estate visible in the expansion card area. I'd rather imagine that these are reserved for some nifty future features than believe that they're just leftovers from scotched portions of earlier designs.

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