The future belongs to multicore processors, and the future of Mac CPUs could well belong to Intel's new 'Core i' series. The new chip architecture makes its Mac desktop debut in this top-of-the-range 27-inch iMac, from where it will surely trickle down through the Mac's family tree.

But what advantages does it offer over the Core 2 Duo or Xeon series? A quick glance at the technical specifications might lead you to believe that this iMac is slower than the other 27-inch model.

Although its Intel Core i5 CPU boasts four processing cores on a single die, it runs at 2.66GHz, whereas the cheaper 27-inch iMac we reviewed last month offers a 3.06GHz Core 2 Duo. But all applications, multi-core capable or otherwise, benefit from the new chip architecture.

Unlike the Core 2 Duo, the i5 – and indeed the faster i7, available as an upgrade option when buying through the online store – connects directly to the memory, doing away with the need for a separate controller. Apple claims this improves the memory bandwidth by up to two and a half times.

Core bench press

And this isn't the only benefit offered by the new architecture. When using an application that doesn't need every core, the processor's Turbo Boost feature shuts off the idle cores while simultaneously increasing the speed of the active ones.

According to Intel, this has the potential to increase the i5 processor's single-core performance to 3.20GHz. Our tests certainly bear this out.

Using Cinebench's CPU benchmark, the top-of-the-range iMac scored 3,869 in its single-core test, a significant step up from its 3.06GHz Core 2 Duo stablemate's mark of 3,498.

Unsurprisingly, it's in the multicore test that the i5's four cores really came into their own. The i5 achieved a score of 12,189 – almost double the dual-core iMac's 6,535. It also shaved around 100 seconds off our QuickTime encoding test, converting a movie to iPod format in 140.5 seconds.

This iMac and its successors look set to prove very popular with video editors and those who do a lot of processor-heavy 3D rendering.

The benchmarks

Cinebench (CBs): CPU and GPU performance rated, Cinebench reports its results as a single figure. Higher is better. Multi-core performance quoted.

Doom 3 frame rates (FPS): Tested using Doom 3's 'timedemo 1' routine, set at 1,024x768 with settings at Ultra. Frames per second quoted. Higher is better.

iTunes encoding (seconds): A timed test using iTunes, ripping an audio CD at 128kb/sec AAC, auto sample rate, no VBR. The lower the time the better.

Verdict

Yet for all its strengths, the Apple faithful have reported problems. Some early adopters had their new computer delivered with a cracked screen, or even failing to power up at all.

MacFormat borrowed two Core i5 iMacs from Apple for testing, and both machines had problems waking from Sleep mode.

The Apple iMac 27-inch 2.66GHz Core i5 is an incredibly powerful computer and a real joy to behold, but our advice is to make sure its teething troubles are resolved before you buy.

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