"Viewing Apple's iMac 27-inch (Late 2012) desktop from the front, it looks at first as if Apple is doing the same thing to the iMac that it did with the new Mac Mini: updating the internal hardware but leaving the exterior unchanged. The edge-to-edge glass over the display, the wide brushed aluminum "chin" below the display, the single piece aluminum stand—it's clearly an iMac. Thanks to upgraded hardware and a new internal design, it is faster and more responsive, offering larger, smarter storage."
Any major computer upgrade generally requires a full software reinstall too. No so if you heed the advice in the guide to Upgrading a Motherboard without Reinstalling. PCSTATS Tips