Apple announced a new iMac desktop which is an update to its previous iMac which was introduced in 2011.The new model brings Intel's third-generation Core CPUs (aka Ivy Bridge) to the iMac, as well as a new thin display.The new display is 5mm thick, making it the thinnest display on any all-in-one. The resolutions remain the same as on the previous generation of iMac desktops, 2,560x1,440 pixels on the 27-inch model, and 1,920x1,080 pixels for the 21.5-inch version.CPU options for the new iMacs include Core i5 and Core i7 chips, along with Nvidia's most recent graphics chips, and up to 32GB of onboard memory. Apple has eliminated the optical drive from the iMac. It has also added a new storage design it's calling Fusion storage, which meshes solid-state and mechanical hard drives into a single storage volume.The 21.5-inch model starts at $1,299 and starts shipping in November. The default model includes a 2.7GHz Core i5 chip, 8GB of memory, a GeForce GT 640 graphics chip, and a 1TB hard drive. The 27-inch version has a starting price of $1,799 and ships in December. Default specs in that model are similar to those of the 21.5-inch iMac, but with a faster 2.9GHz Core i5 CPU, and a higher-end Nvidia GeForce GTX 660M graphics chip.