Power Mac G5 2 GHz dual-core & Power Mac G5 2.3GHz dual-core


“Choose a Power Mac G5 Dual or Power Mac G5 Quad and prepare to be blown away,” Apple's online store boasted when the pro desktops went on sale.

The copy writers may have a point about the Quad, but when it comes to the 2GHz and 2.3GHz dual-core models, a couple of grains of salt are in order. In terms of overall performance, these new machines look, feel and perform pretty much like the models they replace.

However, they have more memory capacity than ever; a new, superfast bus for expansion cards; and graphics capabilities that are sure to appeal to gamers and animators, as well as many scientists and engineers.

1x2 = 2x1
The new machines feature CPUs with two G5 processing engines on a single sliver of silicon. Each dual-core processor has two of everything that defines the G5, including its Velocity Engine. That's something completely new for the Mac, although IBM, Advanced Micro Devices, and others have been using a similar approach on other chips for several years.

The idea of combining two processing engines to boost performance, however, is not new to the Mac. The first dual-processor Power Mac appeared back in 1997, and Apple has consistently offered such systems for the past five years. (Remember the slogan, “Two brains are better than one”?)

The difference is that this system used to require two separate, complete CPUs. With dual-core processors, Apple can include two brains on just one chip. Put simply, G5s with one dual-core processor replace G5s with two single-core processors; in the new dual-core models, even the clock speeds are the same. OS X apparently doesn't see much difference: Apple's System Profiler reports two CPUs, just as in dual-processor systems, and the Activity Monitor works the same way with two cores as it does with two processors.

The Power Mac Quad, by contrast, has two processors with a dual core each, or four processing engines in all - twice as many as any previous Mac. That's the system that really might blow us all away, but it wasn't available for review at press time.

Adding it all up
Switching from dual processors to a dual-core single processor presumably saves Apple a little money, although the company isn't yet passing any savings on to customers. At £1,399 and £1,749, respectively, the 2GHz and 2.3GHz Dual models are priced the same as the two-processor Power Macs they replace.

The switch also saves space and simplifies the challenge of cooling the machine but, again, the benefits aren't yet apparent: the dual-core models have the same big enclosures as their predecessors, with the same elaborate thermal-management system. In fact, there are still two large fans mounted in the front of the processor module, even though there's now only one chip inside.

Of course, there are some differences between the new and old designs. Each core now has 1MB of Level 2 (L2) cache for itself; in the previous Power Mac generation, each CPU had only 512K of L2 cache. On the other hand, each CPU in the dual-processor models had its own high-speed frontside bus for fetching and returning data and instructions; now the two cores on a single chip have to share the same bus.

To add one more variable to the equation, the new Power Macs also take advantage of the latest in DRAM technology. They use 533MHz DDR2 (double data rate 2), also known as PC2-4200, memory, while the previous models used 400MHz DDR chips.

The net effect of all these changes on actual performance? Positive, but nothing to write home about, according to our benchmark tests. In our Speedmark 4 suite and most of our other standard tests, the 2.3GHz dual-core Power Mac G5 outpaced the 2.3GHz dual-processor, but only slightly (see the benchmark chart). Comparing the new 2GHz dual-core model to the previous 2GHz dual-processor model produced similar results.

New slots and graphics cards
The one test in which the 2.3GHz dual-core system left its 2.3GHz dual-processor predecessor in the dust - and even outperformed the 2.7GHz dual-processor model - was our Unreal Tournament 2004 frames-per-second test (see the benchmark chart). These stellar results don't seem to have anything to do with the new G5 processors - they're really a function of the new graphics cards that come with the dual-core systems and the new high-speed slots they sit in.

In the case of the new 2.3GHz Dual (as well as the Quad), the standard card is the nVidia GeForce 6600 with 256MB of video RAM. The stripped-down nVidia GeForce 6600 LE, with 128MB of memory, is standard in the new 2GHz Dual, but if you order from Apple's online store, you can upgrade to the full version for just £30. Both cards have two DVI connectors, one of which is the dual-link variety that's required for Apple's 30-inch Cinema HD Display.

If that's not good enough, Apple is offering two other nVidia upgrade options: the GeForce 7800 GT (£270 for the dual-core 2GHz and £239 for the dual-core 2.3GHz), which promises even faster motion graphics and animation; and the Quadro FX 4500 (£1,140 for the 2GHz and £1,110 for the 2.3GHz), which has 512MB of memory and two dual-link ports, plus an extra connector for stereo 3D goggles.
All these cards take advantage of PCI Express (PCIe), a new (to the Mac) industry-standard architecture for add-on cards. The new slots offer much better throughput and greater flexibility than the AGP, PCI, and PCI-X slots they replace.

So what can you put in them? Besides the nVidia video cards, Apple sells a PCIe Fibre Channel card and Blackmagic Design and AJA Video Systems have released high-bandwidth PCIe video-capture cards for the new Macs. Digidesign says it plans to release PCIe-compatible Pro Tools|HD systems by the end of November. Other cards, particularly for video and audio, but also for 10GB Ethernet and other demanding applications, will undoubtedly appear soon. But for now, there aren't nearly as many choices as Mac professionals have been used to with previous-generation Power Macs.

And don't even think about transferring your existing PCI and PCI-X cards. Although the name makes PCIe sound like an evolutionary heir to the venerable PCI standard, it's a fundamentally different technology and there's no compatibility between old cards and the new slots. Apple is following its usual abrupt approach to technology transitions: out with the old, in with the new. (For people who require compatibility with PCI-X, Apple is keeping the 2.7GHz dual-processor Power Mac G5 on the market, at least for now, at the reduced price of just £1,949.)

With regard to software, the PCIe standard was designed to cause no compatibility issues, but a few applications that specifically look for an AGP graphics cards won't run on PCIe systems. One notable example is Apple's own Final Cut Pro, versions 4.0 through to 4.5. Apple's solution? Upgrade to version 5.0.3 for £279!

Wait, there's more
Other notable changes in Apple's new G5 Power Macs include:
n 512MB of memory is standard, but you can now boost total memory all the way to 16GB, double the previous maximum. (That goes for both Dual models - for a change, Apple hasn't imposed any artificial limitations on the lowest-priced version.) The machines can take advantage of ECC (error-correcting code) memory, an expensive form of RAM that can automatically correct certain memory errors - a technology some government, corporate, and academic customers insist on for mission-critical and computer-intensive applications.

  • The internal 56K modem, made optional in the previous Power Mac generation, has disappeared altogether; if you need dial-up capabilities, your only choice is an external USB modem (Apple's costs £35).
  • In exchange, both dual-core models have two Gigabit Ethernet connectors, so you can dedicate one to a storage-area network (SAN) or an isolated management network in addition to a conventional network. Both ports support an advanced throughput-boosting networking technology known as Jumbo Frames (packets of up to 9,000 bytes).
  • Both Dual systems come with Apple's four-button Mighty Mouse.

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