Up to 1.7x faster at the core.
New quad-core Intel Core i5 processors are standard on the new iMac. Choose a 21.5-inch iMac with a 2.5GHz or 2.7GHz quad-core Intel Core i5. Or expand your view with a 27-inch iMac featuring a 2.7GHz or 3.1GHz quad-core Intel Core i5. You can even configure iMac with the fastest quad-core processor available — the Intel Core i7. That means the new iMac performs nearly twice as fast as the previous generation.

Advanced AMD Radeon HD graphics.
When you need performance for things like playing 3D games, editing HD video, or running design software, the discrete AMD Radeon HD graphics in iMac go to work. You see more frames per second and experience better responsiveness. With up to 2GB of dedicated GDDR5 video memory, these processors provide up to 3x faster performance than the previous generation

Thunderbolt — The fastest, most veratile I/O ever.
Thunderbolt is a revolutionary I/O technology that supports high-res displays and high-performance data devices through a single, compact port. It sets new standards for speed and simplicity. Thunderbolt I/O technology gives you two channels of 10 Gbps throughput in both directions. You can move data to and from peripherals up to 20 times faster than with USB 2.0 and up to 12 times faster than with FireWire 800.

The new FaceTime HD camera.
The better to see you with., Get more of your friends in the picture with crisp, widescreen HD video. The new FaceTime HD camera lets you make FaceTime video calls in 720p resolution. Make HD calls from one new iMac to another or to a new MacBook Pro. You can also make video calls to other Intel-based Mac computers, iPad 2, iPhone 4, or the latest iPod touch