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Core Duo iMacs debut speedy new chips

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What’s an Intel chip doing in an iMac? Almost exactly the same things PowerPC chips do in older models—just faster on some tasks and, for now, slower on others.

As Steve Jobs noted when he rolled out the new iMacs, they have a lot in common with their G5-based predecessors: the same strikingly elegant, space-saving design; the same basic features; and the same prices—$1,299 for an iMac with a 17-inch screen , and $1,699 for a 20-inch model .

Most important, the software on new iMacs looks and feels just like what you’re used to. Apple has provided new versions of Mac OS X (currently 10.4.4) and its iLife apps that run on the Intel processors, but to the user they’re identical to the PowerPC versions for other Macs. And most third-party programs written for OS X on PowerPC also run on the new machines, thanks to a clever technology that Apple calls Rosetta.

The big difference, in theory, is speed. According to Apple’s benchmark tests, the Intel iMacs are roughly twice to three times as fast as the last G5 models. Macworld Lab’s real-world tests, however, reveal a more complex reality, in which speed varies widely depending on what software you’re using.

Over time, as programs are updated, the Intel-based iMacs should gain a wider performance lead over their PowerPC-based predecessors. If you’re thinking of buying now, stop to consider the tradeoffs.

Intel inside

Intel’s advanced manufacturing technology enables the company to put two complete processors on a single slice of silicon—that’s where the Duo part of the name comes from. (Intel has also announced new single-engine chips called—you guessed it—Core Solos, which might show up in future iBooks or other Mac models.) PowerPC maker IBM used the same dual-core approach to increase performance in the G5 processors Apple currently ships in its Dual and Quad Power Mac models, but those chips use too much power and generate too much heat for the close quarters of an iMac or a laptop—one big reason Apple switched from PowerPC to Intel processors.

With clock speeds of 1.83GHz in the 17-inch iMac and 2GHz in the 20-inch model, the Core Duos actually run a shade slower than the 1.9GHz and 2.1GHz G5s in the previous iMacs. The new chips perform better, though, not only because they have two processing engines but also because they include 2MB of Level 2 cache memory—four times as much as the previous iMac G5s had.

The off-processor memory in the new iMacs is also fast—in fact, at 667MHz, it’s the fastest main memory ever shipped in a Mac, faster even than that of the Power Mac Quad. (Technically speaking, it’s PC2-5300 DDR2 SDRAM, and it comes on a notebook-style module called a SODIMM.) There are two easily accessible memory slots, one of which is filled with a 512MB module in the standard configurations, and the system can accommodate a maximum of 2GB.

The iMacs’ video subsystem now features the Radeon X1600, ATI Technology’s latest midrange graphics processor, replacing the aging X600. In both iMac configurations 128MB of video RAM remains standard, but for an extra $75 you can order the 20-inch model with 256MB.

In addition, both new models have a mini-DVI port through which, with the appropriate $19 adapter, you can attach a VGA, S-Video, or composite monitor, or a DVI display such as an Apple Cinema Display (up to 23 inches only). You’re no longer limited to mirroring, either—the new models also support extended-desktop mode.

Apple outside

In other respects, the new iMacs match the iMac G5s introduced last October. As before, the two models come standard with, respectively, 160GB and 250GB hard drives (both 7,200-rpm Serial ATA devices), and both have an 8x SuperDrive with double-layer support. For communication, AirPort Extreme (now with support for 802.11a, 802.11b, and 802.11g), Bluetooth 2.0, and Gigabit Ethernet are built in, but a modem is not. The computer has three USB 2.0 and two FireWire 400 ports. Its audio jacks support both analog and digital optical output, but only analog input. Apple’s wired Mighty Mouse is included.

Two nifty features added to the previous iMacs, the compact Apple Remote Control and the iSight camera built into the bezel above the screen, are also unchanged.

Compatibility and performance

All the Apple software that ships with the new iMacs is fully native on the Intel processors—that is, the code was recompiled for the new chips, so there’s no need for translation or emulation. (Some of the third-party applications bundled with the iMac—Quicken 2006, for example—are not fully native; others, such as Omni Outliner, are.) Only a handful of third-party developers, however, had native versions of their programs available in time for the iMac launch. Major companies such as Adobe and Microsoft weren’t even ready to announce target dates for updates of their programs. Apple said it wouldn’t have Universal versions of its own pro applications ( Aperture [   ], Final Cut Studio, and Logic Pro [   ]) until March 31.

By late January, the number of available Universal programs—that is, programs with native code for both PowerPC and Intel processors—was approaching 500, according to Apple’s count. But many of them were relatively minor programs or shareware utilities ( click here to search Apple’s list of Universal apps).

Even without Universal updates, most up-to-date Mac software runs on the new iMacs anyway, because Rosetta, a feature built into OS X for Intel Macs, automatically translates PowerPC instructions into their Intel equivalents. On the whole, it works amazingly well, but there are some important caveats.

First, Classic software—programs written for Mac OS 9 and earlier—won’t run on the new iMacs. Neither will third-party preference panes and kernel extensions for OS X—categories that include many device drivers, such as those for Microsoft’s keyboards and mice. Many PowerPC Mac games, Microsoft’s Virtual PC (   ), current versions of Apple’s pro apps, and other programs that require very high performance or depend on precise timing, don’t start up at all or run hopelessly slowly on Rosetta.

Second, programs that do run on the translator generally work at roughly half the speed they deliver on PowerPC processors. With today’s hardware, that’s not nearly as bad as it may sound—after all, half of 2GHz is 1GHz, and most programs run acceptably to most users on 1GHz machines. In fact, I scarcely noticed the slowdown when using Microsoft Office on the Intel iMacs; Photoshop CS2 was less responsive than on recent PowerPC Macs, but not painfully so.

On the other side of the ledger, the new iMacs definitely feel quicker when you’re running native applications, whether from Apple or other developers. Though you’ll rarely if ever experience Apple’s touted “2 to 3x faster” performance, booting up is much faster, Web pages visited with Safari snap to the screen, and our tests with a beta Universal version of id Software’s Doom 3 showed a huge increase in frames per second (see the benchmark chart). With the native iLife ’06 applications, performance on the Intel iMacs was better, but in most cases not dramatically so; in a few of our tests, the new machines actually lagged behind the 2.1GHz G5 iMac.


UNIVERSAL iMac Core Duo/2GHz iMac Core Duo/1.83GHz iMac G5/2.1GHz
Startup 0:25 0:25 0:46
iMovie 6: Apply B&W Effect 1:45 1:54 3:11
iMovie 6: Apply Rain Effect 2:05 2:12 2:43
iPhoto 6: Import 100 Files 0:53 0:55 1:22
iPhoto 6: Export to QuickTime 1:08 1:12 1:31
iPhoto 6: Export to File 2:55 3:06 2:40
Finder: Create Zip Archive 2:32 2:44 2:53
Doom 3 v1.3.1303: Universal Beta Demo 1 35.9 27.3 17.0
iTunes 6.0.2: MP3 Encode 1:14 1:20 1:23
iDVD 6: Save as Disk Image 13:55 14:47 16:25
Adobe Photoshop CS2: Suite 2:50 3:02 1:16
Microsoft Word Scroll: Scroll 1:58 2:05 0:57

Best results in red.

All scores are in minutes:seconds, except for Doom 3 test which is frames per second. All systems were running Mac OS X 10.4.4 and had 512MB of RAM. The G5’s processor performance was set to Highest in the Energy Saver preference pane. Using iMovie, we applied 2 different video effects to a 1-minute movie, one at at a time. We imported 100 JPEG photos into iPhoto and then exported them as a QuickTime movie and as files, resized to a maximum of 2,000 by 1,500 pixels. We created a Zip archive from a 1GB folder in the Finder. We ran the Demo 1 test on a beta Universal version of Doom 3, which was set to use Ultrahigh graphics at a resolution of 1,024 by 768; all advanced options were set to Yes except for vertical sync and antialiasing. We converted 45 minutes of AAC audio files to MP3 using iTunes’ High Quality setting. We saved an iDVD project containing a 6:46 movie as a disk image. 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. We scrolled through a 500-page document using Microsoft Word.—Macworld lab testing by James Galbraith and Jerry Jung

Room for improvement

Like their immediate predecessors, but unlike the first-generation iMac G5s back in 2004, the new machines are not user-serviceable—meaning you cannot do simple hardware repairs yourself. And there are some other items on my hardware wish list: a stand design that allows height adjustment; more memory capacity (at least 4GB); a higher-resolution, more flexible iSight camera; and perhaps a FireWire 800 port. On the software side, users who don’t own Microsoft Office may be disappointed to learn that AppleWorks is no longer included; though iWork ’06 is, it’s only a 30-day trial version.

Macworld’s buying advice

If you already have a recent Mac, there’s no particular reason to rush out and buy an Intel-based iMac today—you won’t find the computing experience all that different. Even if you’re due for new hardware, don’t buy a new iMac now if you run software that doesn’t yet run on the Intel-based iMacs. And if you’re still not ready to give up Classic software, either stick with what you have or go out and buy a G5 iMac—while they last.. But for other users, there’s no reason to hesitate: the Intel-based iMacs are already great machines, and they’ll only get better. Spring for the $1,699 model if you can afford it—the extra disk capacity and screen real estate easily justify the extra cost.

[ Henry Norr is a former editor of MacWeek He has been reviewing Mac systems since 1986. ]

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