November 19, 2009, 9:10 PM — When Apple announced new iMacs last month, it included a major step forward amid the subtle-but-welcome refinements in most of the models: the first ever iMac to offer a quad-core processor. The new high-end 27-inch iMacs are the first to use Intel's Core i5 and Core i7 quad-core processors, and they were not available at the time of the announcement. But finally, the wait is over, and the Core i5 and Core i7 27-inch iMacs have arrived--and let me tell you, it was worth the wait.
There are four standard iMac configurations, three of which have 3.06GHz Core 2 Duo processors and were reviewed recently. The fourth standard configuration is a $1999 model that has the same 27-inch screen, 1TB hard drive, and 4GB of RAM as the $1699 27-inch 3.06GHz Core 2 Duo iMac ( Macworld rated 4 out of 5 mice ), but features a more powerful ATI Radeon HD 4850 graphics card with 512MB of GDDR3 memory and Intel's Core i5 quad-core processor running at 2.66GHz. The Core i5 has 8MB of L3 cache shared among the processing cores.
The Core i5 features a technology Intel calls Turbo Boost. If an application isn't using every available core, the cores that are idle shut off, and the active cores speed up. According to Apple, this allows the processor to run up to 20 percent faster under heavy workloads; that translates to 3.2GHz in this iMac.
As an upgrade option to the Core i5 iMac, you can swap in a 2.8GHz Core i7 quad-core processor for $200 more. The Core i7 also features Turbo Boost (for speeds of up to 3.46GHz), and it also has Hyper-Threading technology that can present itself to highly threaded applications as having eight virtual cores.
New 27-inch Core i5 and 27-inch Core i7 iMacs: Speedmark scores
To see how well the new quad-core iMacs perform, we ran our overall system performance test suite, Speedmark 6, and the results were quite impressive. In fact, with a Speedmark 6 score of 209, the 2.66GHz Core i5 iMac is the fastest standard configuration Mac we've ever tested. It was three percent faster overall than the 2.66GHz Quad-Core Mac Pro ( Macworld rated 4.5 out of 5 mice ), and 1.5 percent faster overall than the 2.26GHz 8-core Mac Pro ( Macworld rated 4 out of 5 mice ).