Fun fact, during one of Apple’s (many) trials, a prototype of an iPad surfaced. It dates back to 2002 and looks like an iBook screen without the iBook. In a 4:3 aspect ratio (already), it measured 1 inch thick (2.5 cm) and was powered by a Pentium M (already as well). This mockup 035 was abandoned quite quickly, or rather, the project was put on hold, for Apple to develop the iPhone before revisiting the iPad a bit later.
Mac OS X
Power Mac G3