Nintendo has released some hardware specifications for its newly-announced Wii U. Its internal components weren't detailed but we do have some other interesting information.
The controller is about 1.8 inches thick, almost 7 inches tall, and just over 10.5 inches wide. The touchscreen measures in at 6.2 inches and has a 16x9 aspect ratio. It has an integrated rechargeable battery, accelerometer, gyroscope, rumble, front-facing camera, a power button, microphone, speakers, and two circle pads (Nintendo's name for the unit's not-quite-analog sticks). It's also equipped with all of the same buttons seen on a Wii Classic Controller: a Home button, d-pad, A/B/X/Y buttons, and L/R buttons, plus ZL/ZR. The controller also comes with a stylus as seen above.
Wii U is fully backwards compatible with all Wii games and accessories, including the Wii Remote, Balance Board, Classic Controller, Nunchuk, etc. It can be connected through HDMI, component, S-video, and composite cables (and possible D-terminal). It can output video from 480i all the way up to 1080p, and it can also do six-channel audio output.
The system uses optical discs that are the same physical size as the Wii's 12-centimeter discs. Their storage capacity is currently unknown. It was
rumored at one point to be capable of holding up to 25GB on a single disc; that may turn out to be correct, as the other aspect of that rumor -- eschewing hard drives in favor of flash-based internal storage -- has turned out to be correct. You can expand upon the system's included flash memory by using either SD cards or external hard drives connected through USB (there are four USB ports total).
