Hardware DIY evangelist site iFixit has put up a detailed teardown of the newly-released Kindle Fire HD e-reader. They give the device their usual thorough going-over with spudgers, razor blades, and Torx bits, and it's immediately obvious once the cover is off that this is an entirely different device from the Kindle Fire.
Chief among the differences is the processor, a dual-core Texas Instruments OMAP 4460, which improves on the regular Fire's OMAP 4430 with a higher clock speed (1.5GHz versus 1.0) and improved graphical performance. The OMAP 4460 is also found in several other smartphones and tablets, notably the Samsung Galaxy Nexus and the second-generation Blackberry Playbook.
iFixit notes that the Fire HD is powered by a large 4400maH, 16.43Wh lithium-ion battery; the regular Kindle Fire sports a battery with similar specs, which calls into doubt Amazon's claim that this beefier device will regularly last for its full rated 11 hours of active time.