27-inch Core i5 iMac (with Core i7 option)

Apple introduced the first ever iMac to offer a quad-core processor. The new 27 inch iMacs are the first to use Intel's Core i5 and Core i7 quadcore processors. Although they were not available at the time of the announcement they are finally out and definitely worth the wait.
There are four standard iMac configurations, three of which have 3.06GHz Core 2 Duo proccessors. The forth standard configuration is a $1999 model that has the same 27 inch screen, 1 TB hard drive, and 4GB RAM as the $1699 27 inch 3.06Hz Core 2 Duo iMac but has a more powerful ATI Radeon HD 4850 graphics card with 512MB of GDDR3 memory and Intel's core i5 quadcore processor running at 2.66Hz. The Core i5 has 8MB of L3 cache which is shared among the processing cores.

The Core i5 has a featured technology called Turbo Boost. If an application is not using a lot of the core, the cores that are not being used will shut off, and the active ones will speed up. This allows the processor to run up to 20% faster under heavy work loads.

With the Core i5 iMac and the 2.8GHz Core i7 iMac, Apple has not just blurred the line between consumer and professional systems, but almost totally erased it. The 2.66Hz Core i5 iMac offers faster performance at most tasks than the 2.66GHz Quad-Core Mac Pro. The Core i5 iMac also has more memory and more storage while being $500 less than the 2.66GHz Quad-Core Mac Pro plus with the Core i5 iMac you get a 27 inch screen.