Quad-core power.
The available quad-core Intel Core i5 or Core i7 “Nehalem” processor in the 27-inch iMac puts four processing cores on one die, so data doesn’t have to travel far to get from core to core. This boosts application performance up to 2x over the previous-generation iMac.1 And unlike systems that connect memory to the processor through a separate controller, these quad-core processors connect memory directly to the processor, improving memory bandwidth up to 2.5x.2
Turbo Boost.
A quad-core iMac also benefits from Turbo Boost. If you’re using an application that doesn’t need every core, Turbo Boost shuts off the idle cores while simultaneously increasing the speed of the active ones.