Since the publication of Macworld’s first lab tests of the Intel-based iMac and our subsequent review, there’s been a massive amount of discussion about our results. There’s also been a lot of confusion and plenty of heated discussion. All the while, we’ve continued to test the new Intel macs, including adding some new tests as new Universal applications arrive on the scene.
So as the Intel transition moves into the second month of 2006, here’s an update on what we’ve learned so far about how Intel-based Macs perform.
2x or not 2x?
When Steve Jobs stood on stage at Macworld Expo in January, he claimed that the new iMac ran as much as two to three times faster than the previous iMac, and the new MacBook Pro laptop ran as much as four to five times faster than the PowerBook G4. There was loud applause from the crowd and a sigh of relief from Mac-watchers everywhere.
Of course, as Jobs himself pointed out, those performance claims were based on some very specific tests. When Macworld tested the new Intel-based iMac, we found that speeds varied widely—but that many tasks commonly run by Mac users today only run between 1.1 and 1.3 times as fast (or, if you prefer, 10 to 30 percent faster) on the Intel-based 2GHz iMac as on the 2.1GHz iMac G5. So while Apple’s iMac web pages prominently display a badge proclaiming “2x faster,” the reality is far more complicated—and for most typical uses, far less dramatic.
But let’s be clear: Apple wasn’t fibbing when it reported that certain tests showed that the new Intel iMac was faster than its predecessor by factors from 1.9 to 3.2. However, those tests were carefully selected to show the new iMacs at their very best, ideal cases designed to put the the new Intel Core Duo chip that powers these systems in the best possible light.
We did see similarly dramatic results in a few of our tests. Rendering a 3-D scene using the Java-based program Art of Illusion, the Intel-based iMac was 3.2 times as fast as its G5 counterpart. (It was also faster than a dual-processor Power Mac G5, suggesting that these Intel Macs are much better than PowerPC-based models when it comes to Java performance.) In two tests using a not-yet-public Universal beta of Aspyr’s Doom 3, the new iMac was 1.7 and 2.1 times better. Yet many of our other tests showed comparatively modest speed improvements, with the Intel-based system commonly between 1.1 and 1.3 times as fast as the G5 model.
In tests with two iLife ‘06 applications—iMovie and iPhoto—we found remarkably different performance depending on what features of the programs we tried. For example, the act of applying one iMovie effect to a video clip resulted in a remarkable speed improvement of 1.8 times. But a different effect showed only half the improvement, and yet another showed no speed improvement at all. More strangely, both of our attempts to export from iMovie (to an iPod and to a Web-encoded movie) were slower on the Intel-based Mac. (Apple says it’s investigating the issue.)
Importing 100 photos into iPhoto 6 was 1.5 times faster, and exporting from iPhoto to a QuickTime movie was 1.3 times faster. But exporting iPhoto images to a Web page was only slightly faster. And exporting those images to files was actually slower on the Intel-based Macs.
Other tests—creating a Zip archive in the Finder, encoding an audio file in iTunes, and generating a DVD image (including all required MPEG-2 rendering) in iDVD—resulted in the most common range of speed improvements, between 1.1 and 1.2 times as fast on the Intel-based iMac as on the iMac G5.
Universal application tests
|iMac Core Duo 2GHz||iMac Core Duo 1.83GHz||iMac G5 2.1GHz||X Factor|
|iMovie 6.0 (export to iPod)||6:39||7:14||6:00||0.9|
|iMovie 6.0 (export to Web)||9:20||10:20||3:20||0.4|
|iMovie 6.0 (B&W effect)||1:45||1:54||3:11||1.8|
|iMovie 6.0 (Aged effect)||1:12||1:19||1:12||1|
|iMovie 6.0 (Rain effect)||2:05||2:12||2:43||1.3|
|iPhoto (import 100 JPEGs)||0:53||0:55||1:22||1.5|
|iPhoto (export QuickTime movie)||1:08||1:12||1:31||1.3|
|iPhoto (export Web site)||2:01||2:12||2:12||1.1|
|iPhoto (export files)||2:55||3:06||2:40||0.9|
|Art Of Illusion 2.2||1:55||2:03||6:07||3.2|
Best results in bold; reference system in italic. X Factor refers to the number of times faster the iMac Core Duo 2GHz is versus the iMac G5 2.1GHz (1.0 = identical speed).
Are Two Cores Better than One?
There are numerous reasons for such variations in test results. But by far the most important has to do with the dual-core nature of the Intel Core Duo.
In the past, Macs got faster largely because the clock speeds of the processors got faster—for example, a 1.2GHz PowerBook G4 was clearly faster than a 1GHz PowerBook G4. However, there’s another way to make a Mac faster: add more processors. Apple’s used this approach before. Multiprocessor Power Macs have been available for a while; all the current Power Mac G5 models use dual-core chips, which essentially contain two processors on one physical chip.
Here’s the catch, though: adding processors to a Mac doesn’t automatically boost system speed the way increasing the clock speed does. That’s because programs must be specifically designed to support multiple processors to gain any benefit.
Since powerhouse Power Macs have supported multiple processors for years now, many heavy-duty professional programs—including graphics tools such as Adobe Photoshop, 3-D tools such as Maya and Cinema 4D, and video tools such as Final Cut Pro Studio and Adobe After Effects—have been modified to take advantage of multiprocessing. As Intel-specific versions of such apps arrive, they’ll undoubtedly perform well on these new iMacs.
But these iMacs are consumer systems. And many consumer-level apps don’t really take advantage of multiprocessing. To really take advantage of the Core Duo’s second processor, such programs will need to be updated to add better multiprocessor optimization. (Note that, if you’re running several programs at once, Mac OS X is smart enough to spread them out across multiple processors. That can provide a speed boost if a user is multitasking, switching between several processor-intensive programs at once.)
To find out just how much our test programs took advantage of the iMac’s dual-core chip, we disabled one of the iMac’s two cores and re-ran several of our tests. The results showed, for example, that some tasks in iPhoto (importing images and exporting a QuickTime movie) took advantage of the second processor core much more than others (exporting to files and Web pages). iTunes is very good at using both processor cores for ripping MP3s, while the Finder seems to only use a single processor when creating our Zip archive.
Testing Multiprocessor Performance
|iMac Core Duo 2GHz||
iMac Core Duo 2GHz
|iMovie 6.0 (B&W)||1:45||2:18||1.3|
|iMovie 6.0 (Aged)||1:12||1:43||1.4|
|iMovie 6.0 (Rain)||2:05||2:41||1.3|
|iPhoto import 100 files||0:53||1:29||1.7|
|iphoto to QT Movie||1:08||1:36||1.4|
|iPhoto to Web page||2:01||2:13||1.1|
|iPhoto to file (2k x 1.5k)||2:55||2:59||1.0|
|Doom 3 v1.3.1303 Universal (Beta) demo1||35.9||34.3||1.0|
|Art Of Illusion render||1:55||3:37||1.9|
Rosetta applications in italic. Processor Factor refers to the number of times faster the test ran with both processor cores enabled (1.0 = identical speed).