Externally, the iMac Intel 27" EMC 2639 looks identical to the previous generation, but the interior specs have been upgraded:

3.2GHz quad-core Intel Core i5 processor (Turbo Boost up to 3.6GHz) with 6MB L3 cache

NVIDIA GeForce GT 755M graphics processor with 1GB of GDDR5 memory

802.11ac Wi-Fi

PCIe flash SSD available