iOnApple has reported on a deposition given by Apple design guru Jonathan Ive. The deposition was part of the patent battle between Apple and Samsung. It includes what is thought to be the earliest known photos of the prototype of the device that would later evolve into the iPad we know and love today.
In December 2011, Samsung deposed Apple Senior VP of Industrial Design Jonathan Ive. Ive was shown photos of Apple’s early three- dimensional tablet mockups. These photos apparently date somewhere between 2002 and 2004, and may well be the earliest iPad mockups we’ll ever see.
My recollection of first seeing it is very hazy, but it was, I’m guessing, sometime between 2002 and 2004, some but it was I remember seeing this and perhaps models similar to this when we were first exploring tablet designs that ultimately became the iPad.
So Apple was working with tablet designs possibly as early as 2002.
You can see from the photos that the mockup is much thicker than the iPad turned out to be, probably because of the technology that was available in that time period. You can also see that there is no home button, but the basic form factor is there, with the familiar dock connector is visible in the second photo.