TThe iMac "Core i7" 3.4 27-Inch Aluminum (Late 2012) technically is a "configure-to-order" configuration of the iMac "Core i5" 3.2 27-Inch Aluminum (Late 2012), but also is documented as a separate model for reader convenience. Other than processor (and the corresponding level 3 cache), these two models are identical.
The iMac "Core i7" 3.4 27-Inch Aluminum (Late 2012) features a 22 nm Quad Core 3.4 GHz Intel "Core i7" I7-3770 (Ivy Bridge) processor with four independent processor cores on a single chip, an 8 MB shared level 3 cache, and a NVIDIA GeForce GTX 675MX graphics processor with 2 GB of dedicated GDDR5 memory. It also has a built-in "FaceTime HD" webcam and stereo speakers but lacks an optical drive.
This model has a 27" 2560x1440 LED-backlit 16:9 widescreen IPS display with the "cover glass fully laminated to the LCD and anti-reflective coating." The rear of the case is aluminum and is thicker in the middle and tapers to a razor-thin 5 mm at the edges. Connectivity includes four USB 3.0 ports, dual Thunderbolt ports, Gigabit Ethernet, 802.11n, and Bluetooth 4.0.
In addition to thinner case design, the "Late 2012" iMac models have faster processors, faster architectures, faster RAM faster graphics, as well as different connectivity than the "Mid-2011" iMac line replaced.