Comparing New iMacs to Older Models

Macworld Lab benchmarks serve a couple different purposes. First and foremost, we're attempting to chart the progress of each new Apple hardware release against the previous generation. That way, we can determine if a new desktop or laptop represents a big step forward, modest progress, or no measurable difference at all.

Take the new iMacs, which we reviewed last week at Macworld.com. Our review of the 2.4GHz, 2.66GHz, and 2.8GHz machines contained benchmarks comparing these new systems to their predecessors, released in August 2007. By running those tests, we could point out that the new iMacs improved on the performance of the previous generation without a corresponding increase in price.

The trouble is, people who bought iMacs last summer and fall probably aren't looking to upgrade at this point. Instead, owners of older machines--some of the earlier Intel-based iMacs as well as people holding on to their G5 systems--are the ones most in need of reliable performance test results. And that brings us to another purpose served by our benchmarks--giving owners of older Macs a glimpse into how much of an improvement they can expect if they decide to upgrade.

To that end, we're rolling out another round of benchmarks for the 20-inch 2.4GHz iMac, 20-inch 2.66GHz iMac, and 24-inch 2.8GHz iMac released by Apple at the end of April. This time, we're comparing the new Penryn-powered systems to some real blasts from the pasts--a G5 iMac, an Intel Core Duo iMac, and one of the first Core 2 Duo iMacs released by Apple.

Let's start with the most dramatic comparison: The 20-inch 2.1GHz G5 iMac with built-in iSight camera was released in October 2005 and priced at US$1,699. In its day, it represented the top of the iMac line. It shipped with 512MB of RAM soldered down, leaving just one DIMM slot capable of holding a 2GB DIMM. We run Speedmark with a minimum of 2GB of RAM, so we upgraded this iMac to 2.5GB. The 2.1GHz G5 iMac featured ATI Radeon X600 XT graphics with 128 MB of DDR SDRAM, and a 250GB SATA hard drive.

In our Speedmark tests, we found this two-and-a-half-year-old to be about half as fast as the latest top-of-the-line configuration, the $1,799 2.8GHz Core 2 Duo model. Certain individual tests show even larger performance differences, with the G5 iMac taking more than three times as long to complete our Compressor and iMovie tests. The 2.8GHz iMac, powered by an ATI Radeon HD 2600 Pro graphics card with 256MB of video RAM, also displayed more than three times as many frames per second than the G5 iMac in our Quake 4 tests.

Even today's entry-level iMac--the $1,199 2.4GHz, 20-inch Core 2 Duo--earned a 69-percent higher Speedmark score than the fastest G5 iMac ever released. And of course many of the individual tests showed the new low-end iMac finishing tests in less than half the time of the old G5-based system.

The first Intel-based iMacs released by Apple ran on a Core Duo processor, so we wanted to include that type of system in these tests. Unfortunately, the only surviving Core Duo-based iMac we have on hand is the somewhat stripped-down iMac for Education. This specialty iMac cost $899 when it launched in July 2006. It features a 17-inch LCD, a 1.83GHz Intel Core Duo processor, and 80GB SATA hard drive. This was an iMac built with price, rather than performance, in mind; it features only a combo optical drive, rather than a DVD-burning SuperDrive and Intel's integrated GMA 950 graphics rather than ATI Radeon X1600 graphics found in the other iMacs Apple sold around that same time. For the purpose of this project, we swapped out the iMac for Education's two 256MB DIMMS for two 1GB sticks.

As this educational iMac uses the integrated graphics, it's no surprise that it lagged far behind even the G5 in terms of gaming performance. Comparing this entry-level system to the latest low-end iMac, we found the new 2.4GHz iMac to be 51 percent faster than the 1.83GHz Core Duo iMac in our Speedmark tests. The 2.4GHz iMac was 31 percent faster than the 1.83GHz model in our Photoshop and Cinema 4D tests while finishing the Compressor test in less than half the time of the 1.83GHz iMac. And though the new low-end iMac's game performance is hardly something to boast about, when compared to the 5.5 frames per second the 1.83GHz Core Duo model was able to display in our Quake test, the 30.9 frames per second tallied by the current 2.4GHz iMac doesn't look so bad (even if that score is 56-percent slower than the high-end iMac's 68.1 frames per second score).

We end our trip down memory lane with a look at one of the first of the Core 2 Duo iMacs, the 17-inch 2GHz model released in January 2007. With a price tag identical to the current entry-level iMac, this Core 2 Duo model featured a SuperDrive, 160GB SATA hard drive, ATI Radeon X1600 graphics, and 1GB of RAM (which we upgraded to 2GB for this testing).

In terms of Speedmark, the new 2.4GHz iMac was 16 percent faster than the older 2GHz model. In individual tests, the latest model was 19 percent faster at Cinema 4D rendering, 27 percent faster at Compressor MPEG encoding. The two low-end systems were comparable in our games tests, though the 2.4GHz iMac was faster in both Unreal Tournament and Quake 4. And though the speed differences are not huge, remember that the new low-end iMac also features three more inches of diagonal viewing area, as well as somewhat faster performance, for the same money as the slower 17-inch iMac.

As you can see, real performance progress has been made at each iteration of the iMac. So when does an upgrade make sense? That is entirely based on who you are and what you use your Mac for. The 16 percent overall performance boost between the first entry-level Core 2 Duo and today's low-end iMac may not be significant enough to warrant the investment for many Mac users; however owners of older iMacs, like the first generation of Intel iMacs, will see a more marked improvement in speed and overall performance with one of today's iMacs. And if you're the owner of a G5 iMac, it's obvious that you could be getting a whole lot more done in a lot less time with a modern iMac.

[James Galbraith is Macworld Lab director.]

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