Apple's big tablet secret spilled

McGraw-Hill's CEO thinks Apple's mystery device is a tablet powered by iPhone software.

Apple plans to unveil its "latest creation," widely thought to be a tablet computer, at an event later today.

Harold McGraw, McGraw-Hill's chief, was a guest on CNBC yesterday.

He was asked about the tablet and said Apple will "make their announcement tomorrow on this one" and that "the tablet is going to be based on the iPhone operating system."

McGraw-Hill spokesman Steven Weiss would not confirm the CEO was describing Apple's actual product.

"There has been lots of speculation and we are as eager as anyone to see how the new device can be used to advance education and business information platforms," Weiss said.