Apple on Tuesday introduced new iMac models with next generation quad-core microprocessors, improved graphics performance and Apple’s new “Thunderbolt” I/O technology underscoring the top changes. Prices start at $1,199.

[ad#Google Adsense 300×250 in story]The new iMac sports quad-core Intel i5 processors across the board (with i7’s available as configure-to-order options), along with AMD Radeon HD graphics. Apple says the integrated memory controller on the new processors provides improved video encoding and decoding capabilities.

Thunderbolt is a new I/O interface Apple and Intel introduced in February. Apple debuted the new interface on its MacBook Pro line. Using the same pin connectors that have become familiar to Mac users as the Mini DisplayPort, Thunderbolt supports high-speed connectivity with storage systems and other forthcoming devices. With adapters it can work with Gigabit Ethernet, FireWire and USB peripherals, too. Unlike the MacBook Pro, the new 27-inch iMacs feature two Thunderbolt ports (the 21.5-inch sports one Thunderbolt port).

The iMacs now come with FaceTime HD cameras (and accompanying communications software) that’s compatible with other Intel Macs running FaceTime, as well as iPad 2, iPhone 4, and current iPod touch models. Other features include an aluminum and glass enclosure, IPS LED-backlit display, FireWire 800 port, four USB 2.0 ports, Gigabit Ethernet, audio line in and line out, SuperDrive and SDXC card slot.

The new iMac comes in 21.5-inch and 27-inch configurations. The low-end model sports a 2.5 GHz quad-core processor, AMD Radeon HD 6750M and 500GB hard disk drive for $1,199. A 2.7 GHz i5 model equipped with AMD Radeon HD 6770M and 1TB hard drive costs $1,499. The 21.5-inch models sport a native resolution of 1920 x 1080 pixels.

The 27-inch comes in a $1,699 2.7 GHz i5 model, equipped with AMD Radeon HD 6770M and 1TB hard drive, or a 3.1 GHz quad core i5, AMD Radeon HD 6970M and 1TB hard drive for $1,999. The 27-inch models sport a native resolution of 2560 x 1440 pixels.

All systems now ship with 4GB RAM installed, configurable to 16GB.