Comparing Apples to Apples: When Is Macintel Faster? When Does PowerPC Make More Sense?

Comparing Apples to Apples

We're starting to see more benchmark comparisons of older PowerPC Macs and new Intel Macs. Some are quick and dirty. Some are fairly extensive. And each one finds something different.

Core Duo vs. G5 Quad

MacSpeedZone (MSZ) published one of the more extensive comparisons last week and also delved into the single-core G5 vs. dual-core Intel vs. twin dual-core G5 comparisons. One of their findings was that a 2.0 GHz Intel iMac trails a 2.5 GHz Power Mac G5 Quad by only 14% when encoding a single QuickTime video.

But when encoding two QuickTime videos at once, the G5 Quad was over twice as fast as the Intel Duo Core.

If that doesn't get your attention, you're not paying attention. Both computers encode a single QuickTime at about the same speed, but the Core Duo uses 87% of its processing capacity to do so. The G5 Quad uses only 42% of its processing capacity for the same task.

That means the G5 Quad can handily run two QuickTime streams at once with capacity to spare (MSZ measured it at 87% of capacity) while the Intel Core Duo only has 13% more capacity to give. Hence, it takes a lot longer to encode two QuickTime videos than one.

Caveat Emptor

While we are comparing Apples to Apples here, we are comparing three very different machines.

• 17" iMac G5/1.8 GHz - ATI Radeon 9600 graphics - PCI/AGP architecture
• 20" iMac Core Duo/2.0 GHz - ATI Radeon X1600 graphics - PCI Express architecture
• Power Mac G5/2.5 GHz Quad - nVidia GeForce 6600 graphics - PCI Express architecture

We're assuming MSZ is comparing the 17" 1.8 GHz iMac G5. Although it's not explicitly stated, this is the only 1.8 GHz iMac they've benchmarked to in the past.

The machine we wish MSZ had tested is the October 2005 iMac G5, which is available in a 17" 1.9 GHz model and a 20" 2.1 GHz one. These two models use the same PCI Express architecture found in the latest Power Macs and iMacs. That would have been a much more fair comparison. The older iMac G5 had a slower memory bus.

If you haven't already followed the link to the comparison on MSZ, take the time to do so now. It's a very good discussion of CPU capacity and the benefits of multiple cores.

Core Duo vs. Single-Core G5

MacSpeedZone runs 16 different benchmark comparisons of a 1.8 GHz iMac G5 and a 2.0 GHz iMac Core Duo. Despite having a 10% faster clock speed and dual cores, the Intel iMac won just 7 of these comparisons - and it took one of them by just 7%, so a 2.1 GHz iMac G5 probably would have beat it.

One thing we see a lot with the single-core G5 is 100% processor usage during benchmark tests. QuickTime encoding, AltiVec Fractal, Graphics - Interface, Dual QuickTime encoding, Photoshop Filters, Photoshop Workflow, Fractographer, and two of four Cinebench (CB 2003) benchmarks all push the CPU to the max. On top of that, the Word Macro and iDVD Import tests tied up 97% of the G5's capacity.

The Intel Core Duo shows its stuff when running Intel-native code. QuickTime encoding only ties up 87% of its dual-core capacity, and it only takes 40% as long to complete this task as the 1.8 GHz iMac G5.

The iMovie Import comparison is impressive. The Core Duo completes the task in 108 seconds using just 7% of its capacity while the G5 needs 181 seconds and uses 45% of its capacity to run the same test. Likewise, the iDVD Import test takes 36.5 seconds on the new Macintel at 77% of CPU capacity vs. 95.6 seconds for the G5, which uses 97% of its capacity.

From this we learn that Intel has really tweaked their CPU for A/V work. If you're ripping tracks to iTunes, encoding videos in QuickTime, and working in iMovie, you've found the area where Intel's Core Duo excels.

G5 Rocks with PowerPC Programs

Where the Intel iMac loses out is running older software that has to use Rosetta PowerPC emulation. The 1.8 GHz iMac G5 handily outperforms the 2.0 GHz iMac Core Duo on the Word Macro, Photoshop Filters, and Photoshop Workflow benchmarks. Word and Photoshop have not yet been ported to the new Intel CPUs, and it shows.

The G5 also wins all four Cinebench comparisons, processes that can at times push both PowerPC and Intel to 100% CPU utilization. Cinebench 2003 comes in regular OS X and G5 optimized versions, but it's not yet Intel native on the Mac.

Caveats

As we noted, all things are far from equal in these comparisons. The iMac G5 has a slower CPU, a different graphics processor, and an older hardware architecture. Game Performance and Graphics - Interface benchmarks would undoubtedly be better with the October 2005 iMac G5 that has a better graphics processor and PCI Express architecture.

Further, a 20" display (as found in the 2.0 GHz iMac Core Duo) is more demanding of the graphics processor than a 17" display (as found in the 1.8 GHz iMac G5), which might also impact these two benchmarks.

Insights

The biggest revelation in MSZ's comparison is the efficiency of the Intel Core Duo processor. When running benchmarks that use Intel-native code, the Intel iMac is always faster while usually using less of its capacity. That means that other processes will run more smoothly, since the CPU has capacity to spare.

The other important finding is that Rosetta PowerPC emulation doesn't hold a candle to a real PowerPC processor - not even with a dual-core Intel CPU at a slightly higher clock speed.

For the primary consumer digital hub applications - iTunes, iPhoto, iMovie, iDVD, and watching DVDs or QuickTime videos - Intel's A/V optimized architecture, the dual cores, and the fact that these apps are all Intel native makes the new Macintel models great choices.

For those who rely on programs that haven't yet been ported to Intel, the Rosetta penalty can be substantial. If you use Photoshop, Word, Excel, AppleWorks, Quark, or other pre-Intel apps extensively, switching to Macintel may reduce your productivity. (If you depends on Classic, don't even think about going Macintel until you eliminate your dependence on Classic.)

Looking Forward

Every week a few more apps are available as universal binaries. If you're considering a transition to Intel, you might want to keep a scorecard of the apps you use on a regular basis. How many are now available as "universal binaries" so they'll run natively on Intel Macs?

There's a lot of potential for software developers here. Until Microsoft Office and AppleWorks are available as universal binaries, there's an opening for a new office suite or integrated app to make inroads. (I can't for the life of me understand why Apple is letting a great program like AppleWorks languish.) Until Adobe ports Photoshop and Elements to Macintel, someone else could step into the gap.

Another possibility is an improved PowerPC emulator. Rosetta is a remarkable hack, but perhaps there are better ways of doing what it does. A program that could analyze your existing PowerPC software and generate optimized replacement code (instead of doing it on the run) could find a ready audience. I remember when Connectix Speed Doubler was on the market, giving Macs not only faster copying but also better 680x0 emulation than Apple had. There's always a market for something better.

And there's definitely a market for a Classic emulator. There are some very nice programs (including Claris Home Page, Claris Emailer, Microsoft Word 5.1a, pre-OS X versions of Photoshop) that fit like an old shoe, and a lot of Mac users see no reason to buy a newer version of these programs. They would, however, like to migrate them to each new Mac they buy. I'm still content with Home Page, Photoshop 5.5, and Calculator II.

In the long run, the dual-core Intel Macs are going to become better options as more software is compiled with universal binaries, emulation improves, and CPUs get faster. They are the future of the Mac, although some users would do well to postpone that future until they can be sure they'll be more productive on the new hardware.

The Low End Equation

And that begs a whole different question: Even if Rosetta is slower on a Core Duo than PowerPC code is on a G5 at the same clock speed, is Rosetta going to be faster than the 400 MHz PowerBook G5, 1.25 GHz eMac, or Power Mac G4/1 GHz Dual?

Looking again at MSZ's results, even the 1.83 GHz iMac Core Duo should at least match performance of a 1.25 GHz G4 on the Word Macro test, and the 2 GHz model should outperform a 1.25 GHz G4 for Photoshop work.

In short, if you have a 1.5 GHz or faster G4 or G5, you're probably better of sticking with PowerPC until the bulk of your software is Intel native. And if you have a 1 GHz or slower Mac, Rosetta emulation will let the Macintel iMac and MacBook Pro outperform your old hardware in almost every instance.

The only real stumbling block for a lot of longtime Mac users is losing Classic.

Link: Wow! The Intel iMac Is Almost As Fast As The Quad Core Power Mac, MacSpeedZone