Preview at WWDC likely in June, followed by September launch.
Apple's Early Prototype iPad Had a 12-Inch Display
BuzzFeed has now posted new photos showing the prototype in full color next to an iPad 2, a comparison which shows the prototype to carry a much larger screen than seen on the iPad to date. Measuring pixel counts against the ruler shown in several of the photos reveals that the prototype device had a display measuring almost exactly 12 inches diagonally.
Compared to the eventually-released iPad's 9.7-inch screen, the prototype device would have had roughly 40% more screen real estate, although it is unknown at what resolution the early device was projected to run.
The prototype otherwise bears a distinct similarity to Apple's iBook of the time, carrying a white plastic shell with rounded corners and a 4:3 aspect ratio for the display. The prototype iPad measures in at just under 1-inch thick, compared to 1.35 inches for the white iBook models and the 0.34-0.50 inch range of the iPad models released to the public so far.