First Lab Tests: iMac with Intel Core Duo processor

Rosetta: Half-speed compatibility

One of the biggest mysteries about the Intel transition has been Rosetta, the technology that lets Intel-based Macs run programs compiled for Macs containing PowerPC processors. Just how fast will Rosetta run non-Universal programs? With this new iMac, we’re finally able to get the first clear answer to that question.

We tested three different non-native applications on the Intel-based iMac, and compared the results to the iMac G5. All of the tests showed that PowerPC applications run on the new iMac at less than half their native speed. Our standard Microsoft Word scrolling test ran at 48 percent of the speed it ran on the iMac G5; our standard battery of 14 Photoshop CS tasks ran at 45 percent of the G5's speed; an MP3 encode using the non-native iTunes 6.0.1 ran at 34 percent of the speed.

Unlike most of Apple’s applications, BBEdit 8.2.4 offers an “Open using Rosetta” option that forces a Universal application to run in Rosetta. As a result, we were able to re-run our BBEdit test on the Intel-based iMac, but this time in Rosetta. The results were very much in line with our other tests: our BBEdit test took roughly twice as long to run within Rosetta as it did when allowed to run natively on the Intel processor.

First Tests: Applications in Rosetta

iMac Core Duo/2GHz iMac G5/2.1GHz Times as fast as G5
iTunes 6.0.1 3:41 1:16 .34x
Photoshop CS2 2:50 1:16 .45x
Word Scroll 1:58 0:57 .48x

Best results in bold.

All scores are in minutes:seconds. All systems were running Mac OS X 10.4.4 with 512MB of RAM, with G5’s processor performance set to Highest in the Energy Saver preference pane. We converted 45 minutes of AAC audio files to MP3 using iTunes’ High Quality setting. We scrolled a 500-page document using Microsoft Word. The Photoshop Suite test is a set of 14 scripted tasks using a 50MB file. Photoshop’s memory was set to 70 percent and History was set to Minimum.—Macworld Lab testing by James Galbraith and Jerry Jung

The big question is, will applications running at half speed within Rosetta be fast enough for users? Many applications aren’t particularly processor-intensive, and will probably seem quite usable under Rosetta. (Microsoft Office, for example, will probably be fairly usable.) Other hard-working applications—Photoshop comes to mind—won’t fare as well. And using a non-native rendering application or game would seem to be a no-go.

The speed of Rosetta will also depend a lot on your perspective. Yes, if you’re upgrading to an Intel-based iMac from an iMac G5 you bought just a few months ago, all of your non-Universal software will run at half speed. But if you’re upgrading from a two- or three-year-old iMac, the speed difference may be much less noticeable.

The speed of applications running under Rosetta will be something to keep in mind, especially when it comes to the forthcoming release of the MacBook Pro. The users of that professional-level laptop are far more likely to demand serious speed from their applications; if there’s no Universal version of Photoshop available at the time, professional photographers may balk at the idea of running Photoshop at a fraction of its speed.

What it means

If you talk to both Apple and Intel, they’ll tell you that the Intel Core Duo is a processor designed for laptops, providing a compromise between performance and good power-consumption and heat-generation characteristics. And so the Core Duo processor in these new iMacs (as well as the forthcoming MacBook Pro) is clearly not meant to be the be-all, end-all when it comes to raw computing power.

That’s one reason why Apple’s initial speed claims of doubled performance (with some tests running showing as much as a 3x speed boost) were so breathtaking, since they were coming from a chip meant to run small and cool. Unfortunately, our tests suggest that the remarkable results of Apple’s published tests aren’t reflected in most of the real-world applications we tested. Based on our initial tests, the new Core-Duo-based iMac seems to be 10 to 20 percent percent faster than its predecessor when it comes to native applications, with some select tasks showing improvement above and beyond that.

Potential iMac buyers who predominantly rely on applications that aren’t available in Universal versions (or, for that matter, those who rely on Classic, which is incompatible with Intel-based Macs) will likely not be interested in these first Intel systems. Running a handful of programs in Rosetta seems reasonable, but if you rely on numerous applications that aren’t yet Universal, it’s probably wise to wait.

After running these tests, several questions come to mind—and they impact the entire Mac product line, not just the iMac. How optimized is Mac OS X 10.4.4 for Intel processors, and will Apple be able to improve performance on these systems over time? Is there room for improvement in the optimization of individual applications, or is this all we’re going to get? How quickly will Intel improve processor performance from here, both in the Core Duo line and in other chip lines that will wend their way into future Apple products?

We don’t have all those answers yet, although several conversations with Apple representatives have suggested that developers will be able to improve the performance of their software as they become more comfortable with the new Intel architecture. Even Apple’s own freshly-released iLife ’06 applications could stand to be better optimized—and Apple representatives admitted as much to us.

How much speed can be wrung out of future improvements to software and the operating system itself? We simply don’t know. There’s reason for hope, but there’s much more testing to be done, many more Universal applications to be written, and more Mac OS X system updates to be released.

[ Jason Snell is the editorial director of Macworld . ]

(Updated on January 18 at 4:46 PM ET to add "times faster than" equivalents to charts. Updated again at 5:35 PM ET to attempt to clarify percentages slower v. percentages faster v. times as fast. Updated on January 20 at 1:43 PM ET to correct a line in the story text which switched the description of two iPhoto tests.)

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